Module 33: Special Locations -- Nails (Onychoscopy)
1. Learning Objectives
After completing this module, the learner should be able to:
- Describe the anatomy of the nail apparatus relevant to dermoscopic examination, including the proximal and distal nail matrix, nail plate, nail bed, hyponychium, cuticle, and paronychium.
- Perform a systematic dermoscopic examination of the nail unit using appropriate technique, including nail plate dermoscopy, free-edge dermoscopy, and intraoperative dermoscopy of the nail matrix.
- Differentiate melanocytic from nonmelanocytic causes of nail pigmentation based on background color, presence of melanin inclusions, and pattern analysis.
- Distinguish regular (benign) from irregular (malignant) patterns of longitudinal melanonychia by analyzing micro-line color, thickness, spacing, and parallelism.
- Recognize Hutchinson sign, micro-Hutchinson sign, pseudo-Hutchinson sign, and atypical Hutchinson sign and explain the diagnostic significance of each.
- Identify dermoscopic features of subungual hemorrhage, including globular proximal edge, filamentous distal edge, color evolution, and migration with nail growth.
- Apply the diagnostic algorithm for melanonychia evaluation and the ABCDEF rule to triage nail pigmentations for biopsy versus monitoring.
- Recognize dermoscopic features of non-melanocytic nail conditions, including onychomycosis, nail psoriasis, lichen planus, subungual exostosis, onychomatricoma, onychopapilloma, squamous cell carcinoma, and glomus cell tumor.
2. Prerequisites
- Module 01: Introduction and Principles of Dermoscopy (dermoscope types, contact vs. noncontact technique, immersion media)
- Module 03: Pattern Analysis (foundational vocabulary for colors, structures, and patterns)
- Module 04: Two-Step Algorithm (melanocytic vs. nonmelanocytic differentiation framework)
Recommended additional background:
- Knowledge of acral dermoscopy concepts (parallel ridge pattern, parallel furrow pattern) is helpful, as similar volar-skin patterns may appear on the hyponychium and paronychium.
3. Key Concepts
3.1 The Nail Apparatus -- Functional Anatomy
The nail apparatus is a specialized cutaneous structure comprising several distinct components, each of which contributes to the dermoscopic picture:
- Proximal nail matrix: Generates the superficial (dorsal) portion of the nail plate. A melanocytic lesion here deposits pigment in the upper layers of the nail plate.
- Distal nail matrix: Generates the deep (ventral) portion of the nail plate. A melanocytic lesion here deposits pigment in the lower layers.
- Nail plate: The keratinized structure that grows longitudinally. It serves as the primary surface for dermoscopic evaluation.
- Nail bed: The soft tissue beneath the nail plate, extending from the lunula to the hyponychium. Vascular patterns are assessed here when the nail plate is eroded or absent.
- Cuticle (eponychium): The thin skin fold overlying the proximal nail plate. Pigmentation here constitutes Hutchinson sign or pseudo-Hutchinson sign.
- Paronychium (lateral nail folds): The skin flanking the lateral borders of the nail plate.
- Hyponychium: The epithelium beneath the free edge of the nail plate. Examination may reveal pigmented patterns analogous to those on volar skin.
- Lunula: The visible, pale, crescent-shaped portion of the distal nail matrix.
3.2 Onychoscopy -- Definition
Onychoscopy refers to the dermoscopic examination of the nail unit. It encompasses:
- Nail plate dermoscopy: Standard examination of the dorsal surface of the nail plate, cuticle, paronychium, and hyponychium.
- Free-edge dermoscopy: Examination of the distal, transversely cut free edge of the nail plate to determine whether pigment resides in the upper or lower portion, thereby localizing the melanocytic lesion to the proximal or distal nail matrix, respectively.
- Intraoperative dermoscopy: Direct examination of the exposed nail matrix and nail bed during biopsy using noncontact polarized light, enabling targeted sampling without contaminating the surgical field.
3.3 Key Terminology Reference
| Term | Definition |
|---|---|
| Longitudinal melanonychia (LM) | A longitudinal pigmented band on the nail plate caused by melanin deposition from the nail matrix |
| Melanonychia striata | LM characterized by visible longitudinal micro-lines (striations) within the band |
| Micro-lines (striations) | Fine longitudinal lines within a pigmented nail band, visible only with dermoscopy |
| Hutchinson sign | True pigmentation of the periungual skin (cuticle, paronychium, or hyponychium) |
| Micro-Hutchinson sign | Pigmentation of the cuticle visible only with dermoscopy, not with the naked eye |
| Pseudo-Hutchinson sign | Apparent pigment in the cuticle due to visualization of nail plate pigment through a translucent cuticle; no diagnostic significance |
| Atypical Hutchinson sign | Pigmentation of periungual skin in locations other than the cuticle (paronychial skin or hyponychium) |
| Polychromia | Presence of four or more colors within a nail lesion |
| Subungual melanoma (SUM) | Melanoma arising from the nail matrix |
| Melanocytic activation | Increased melanin production without an increase in melanocyte number (<6.5 melanocytes/mm of basal membrane) |
| Melanocytic hyperplasia | Increased number of melanin-containing melanocytes (>6.5 cells/mm of basal membrane) in the basal and suprabasal layer |
4. Core Content
4.1 Introduction and Clinical Significance
Longitudinal pigmentation of the nail can be caused by a broad spectrum of conditions, ranging from post-traumatic pigmentation and nail infection to melanoma. Clinician anxiety regarding nail pigmentation typically stems from two factors: uncertainty about the underlying diagnosis, and reluctance to perform a nail matrix biopsy due to the risk of pain and permanent nail dystrophy. Compounding this difficulty, nail matrix biopsies performed by inexperienced physicians often yield nail plate fragments rather than nail matrix tissue, rendering histopathologic interpretation unreliable.
Dermoscopy provides increased diagnostic accuracy in the evaluation of the nail unit, helps differentiate melanocytic from nonmelanocytic processes, and can guide the location and extent of a nail matrix biopsy. Importantly, early melanomas of the nail matrix can be difficult to diagnose both dermoscopically and histopathologically, requiring integration of clinical factors (age of onset, digits involved, history of change) to avoid both unnecessary biopsies and melanoma underdiagnosis.
4.2 Patient History and General Physical Examination
Before dermoscopic examination, the following historical features should be assessed, as they affect the probability of melanoma:
- Duration: Pigmentation present since birth or early childhood usually corresponds to a congenital nevus (reassuring). The later an acquired pigmented band appears in life, the higher the probability of melanoma.
- History of melanoma: A personal or family history of melanoma increases overall melanoma risk, though evidence for a specific increase in subungual melanoma risk is insufficient.
- Digits involved: Isolated nail pigmentation of the thumb, index finger, or hallux carries a greater likelihood of being melanoma compared with pigmentation of other digits or multiple digits.
- History of trauma: Many patients with SUM recall a prior trauma to the involved digit, though it remains unclear whether this association reflects recall bias or a true biologic phenomenon.
- Change: Progressive darkening or widening of an acquired pigmented nail band in an adult over months should raise concern. Patients may be asked to search their smartphone photo library for prior images showing the nail over time.
- Patient activities and medications: Athletic activities, recent trauma, physical exertion (e.g., long hiking), anticoagulant use (aspirin, warfarin), and medication history (including intravenous agents) may help identify subungual hemorrhage or drug-induced causes.
Key Takeaways
- Melanonychia striata (longitudinal pigmented nail band) is evaluated by assessing band width, color regularity, parallelism of lines, and periungual pigmentation.
- Regular, parallel, evenly colored brown lines in a narrow band correspond to melanocytic activation or benign nevus, while irregular lines with variable width and color raise melanoma concern.
- In adults, a new or changing melanonychia involving a single digit requires dermoscopic evaluation and consideration of biopsy, particularly for the thumb or great toe.
4.3 Clinical and Dermoscopic Examination
A complete examination includes inspection of all nail units on the hands and feet. For each digit, the following should be evaluated: the nail plate, cuticle, paronychium, and hyponychium. Additionally, examination of mucosal surfaces (mouth, genitalia) can aid in identifying systemic conditions that involve nails and mucosae (e.g., Peutz-Jeghers syndrome, Laugier-Hunziker syndrome).
4.4 Dermoscopic Technique for the Nail Unit
4.4.1 Immersion Medium
For nail plate dermoscopy, a viscous solution is preferable to alcohol. Ultrasound gel or clear gel-based hand sanitizer is recommended because the viscosity allows it to remain on the nail plate and fill concavities without rolling off. During examination, varying the focus of the dermoscopic device helps evaluate the depth of pigmentation.
4.4.2 Free-Edge Dermoscopy
Examination of the free (distal) edge of the nail plate provides critical clues:
- Localizing the melanocytic lesion: Pigment in the upper portion of the free edge indicates a proximal nail matrix origin; pigment limited to the lower portion indicates a distal nail matrix origin. This information guides biopsy location.
- Identifying nail tumors: The honeycomb-like pitting of onychomatricoma and the subungual hyperkeratosis of onychopapilloma or SCC are best seen at the free edge.
- Fontana-Masson staining: When doubt persists, a nail clipping stained with Fontana-Masson can facilitate visualization of melanin distribution and help determine pigment origin.
4.4.3 Intraoperative Dermoscopy of the Nail Matrix
Using noncontact polarized light, the nail matrix can be examined directly during surgery without risk of contaminating the sterile field. Key intraoperative findings include:
- Streaks, pigment network, and globules: Most commonly seen in melanocytic hyperplasia.
- Regular stripes and/or globules: Favor benign lesions.
- Irregular stripes (variable color, length, thickness) and asymmetrically distributed globules: Favor melanoma.
- Diffuse homogeneous pigmentation: Seen in melanocytic activation without hyperplasia (e.g., ethnic-type pigmentation).
- Irregular translucent whitish areas with atypical vessels: Squamous cell carcinoma.
- Purple ovoid spots: Glomus cell tumor.
- Regular longitudinal translucent whitish area with longitudinal vessels: Onychopapilloma.
- Multiple hyperbolic crypts ("Sagrada Familia sign") and proximal digitations with mirror sign: Onychomatricoma.
Check Your Understanding
What special dermoscopic technique is recommended for examining the nail unit?
Gel (ultrasound or antibacterial gel) is recommended as the interface fluid because its viscosity keeps it in place on the convex nail surface. The dermatoscope should be applied with minimal pressure to avoid compressing vessels. Both the nail plate and free edge should be examined, as well as the periungual skin.
Key Takeaways
- The micro-Hutchinson sign (periungual pigmentation visible only under dermoscopy) is a key indicator of nail apparatus melanoma in adults and should prompt matrix biopsy.
- Free-edge dermoscopy localizes the melanocytic source: pigment in the upper free edge indicates proximal matrix origin, while pigment in the lower edge indicates distal matrix.
- Intraoperative dermoscopy of the nail matrix can guide biopsy selection and identify the irregular pattern (variable lines, irregular dots/blotches) diagnostic of melanoma.
4.5 Nail Dermoscopy Semiology
4.5.1 Blood Spots (Subungual Hemorrhage)
Blood spots are the dermoscopic hallmark of subungual hemorrhage. Their key features include:
- Proximal edge: Sharply demarcated, round-shaped.
- Distal edge: Filamentous (elongated parallel linear pattern), resulting from blood moving distally via capillary action.
- Color: Varies from purple-red (fresh blood) to black-brown (older blood).
- Association: Typically trauma-induced, including repetitive microtrauma from tight or poorly fitting shoes, and anticoagulation therapy.
Critical caveat: Blood spots may occasionally arise from bleeding within an underlying tumor. Before diagnosing uncomplicated subungual hemorrhage, the entire nail plate, free edge, hyponychium, eponychium, paronychium, and cuticle must be examined. Blood spots can be attributed to trauma only if a portion of the proximal nail plate is visible and appears normal. If no normal proximal nail plate is visible, re-examination in 3-4 months is mandatory to confirm that the blood migrates distally with nail growth. Subungual hemorrhage moves distally approximately two-fold slower than the nail plate itself.
4.5.2 Background Pigmentation
Brown Background Pigmentation
A longitudinal band with a brown background indicates the presence of a melanocytic proliferation in the nail matrix. This is observed in nail matrix nevi and melanomas. The color varies from light brown to dark brown to black, with skin types I-IIIa tending toward lighter coloration and skin types IIIb-VI toward darker bands.
Gray Background Pigmentation
A gray coloration indicates melanocytic activation without significant melanocytic proliferation. Conditions associated with gray bands include:
- Ungual lentigo
- Drug-induced pigmentation (e.g., hydroxyurea, bleomycin, minocycline, AZT)
- Endocrine nail pigmentation
- Ethnic-type pigmentation
- HIV-associated nail pigmentation
- Inflammatory nail disorders
- Laugier-Hunziker syndrome
- Nutritional nail pigmentation
- Traumatic nail pigmentation (including frictional toenail pigmentation)
- Systemic lupus erythematosus and scleroderma
A single gray band involving a single digit may, on very rare occasions, be seen in early melanoma in situ or Bowen disease. However, gray lines involving multiple digits are a reassuring sign associated with benign diagnoses.
4.5.3 Parallel Micro-Lines (Striations) Over a Brown Background
Melanonychia striata due to melanocyte proliferation consists of a pigmented band that typically extends the entire length of the nail plate. Within this band, dermoscopy reveals multiple linear micro-lines (striations) that can demonstrate either a regular or an irregular pattern.
Regular Pattern (Benign)
- Lines with similar colors and uniform thickness
- Organized (even/symmetric) spacing
- Lines that are parallel to each other and extend the entire length of the nail plate
- Background band is homogeneously brown
- Minimal variation in shades of brown throughout the lesion
- Associated with melanocytic nevi of the nail matrix
Irregular Pattern (Concerning for Melanoma)
- Lines with variable color (white, light brown, dark brown, gray, or black)
- Lines with differing intensity of pigmentation
- Increased variability in line thickness
- Uneven or asymmetric (disorganized) spacing
- Lines that do not extend completely from proximal to distal nail plate
- Lines that are not parallel to each other and may merge (disruption of parallelism)
- In rapidly growing melanomas, the band adopts a triangular configuration (wider proximally, narrower distally)
- Blood spots and splinter hemorrhages may coexist
- Associated with melanoma of the nail matrix
4.5.4 Hutchinson Sign and Variants
Pseudo-Hutchinson Sign
Visualization of pigment in the nail plate located beneath a translucent cuticle. This is not true pigmentation of the cuticle itself. It has no particular diagnostic significance and should be distinguished from true Hutchinson sign.
Hutchinson Sign and Micro-Hutchinson Sign
- Hutchinson sign: Melanin pigmentation within the periungual skin (cuticle). When associated with melanonychia striata, it is highly suggestive of melanoma, but can also occur in congenital nevi of the nail unit.
- Micro-Hutchinson sign: Focal, very small areas of pigment within the cuticle that are imperceptible to the naked eye but visible with dermoscopy. Associated with melanoma but also observed in ethnic-type pigmentation and congenital nevi.
- Important: Biopsy of the pigmented cuticle (Hutchinson sign) alone cannot rule out melanoma of the nail matrix. A matrix biopsy is required.
Atypical Hutchinson Sign
Pigmentation located in areas other than the cuticle -- specifically on the paronychial skin or on the hyponychium. The rules for evaluating pigmented lesions on volar skin apply here: a parallel ridge pattern or irregular diffuse pigmentation should raise concern for melanoma.
4.5.5 Longitudinal Xantho-Leukonychia
Leukonychia (white band) and xanthonychia (yellow band) are often observed simultaneously within the same lesion. This phenomenon is generally due to thickening of the nail plate and can be seen in epithelial tumors of the nail matrix (onychomatricoma, onychopapilloma, SCC).
4.5.6 Longitudinal Splinter Hemorrhages
Splinter hemorrhages under the nail plate are associated with numerous conditions:
- Multiple nails involved: Connective tissue diseases, onychotillomania, coagulation abnormalities, undernutrition, infectious endocarditis, hematological disorders.
- Single digit with leuko-xanthonychia or polychromia: Suspect an epithelial tumor of the nail matrix.
- Randomly distributed with erythronychia: Suspect amelanotic melanoma.
- Associated with benign tumors: Onychopapilloma and onychomatricoma.
4.5.7 Longitudinal Erythronychia with Enlarged Proximal Origin
Angiomas of the nail plate present dermoscopically as a thin longitudinal erythronychia with a clubbed proximal edge.
4.5.8 Localized Subungual Hyperkeratosis with Distal Triangular Onycholysis
When seen at the free edge and associated with leuko-xanthonychia, splinter hemorrhages, or polychromia, this finding is indicative of an epithelial tumor (ranging from benign onychomatricoma/onychopapilloma to malignant SCC). A triangular erosion (onycholysis) of the distal nail plate should prompt further evaluation.
4.5.9 Polychromia
Defined as the presence of four or more of the following colors: black, red, blue, white, yellow, dark brown, light brown, gray, or purple. Polychromia is seen in malignant amelanotic neoplasms, including SCC and amelanotic melanoma.
4.5.10 Atypical Vessels
Atypical vessel patterns visible on the nail bed (when the nail plate is eroded) are a hallmark of advanced malignant tumors. An atypical pattern is defined by at least one of:
- Linear and irregular vessels: Caliber changes from one segment to another of the same vessel.
- Three or more vessel types within the same lesion: dots and globules, comma-like, hairpin-like, linear, corkscrew-like, or arborizing vessels.
- Milky-red areas: Structureless pink areas with various shades of pink without identified vascular structures. Found in pyogenic granuloma and advanced amelanotic melanoma; since these two entities cannot be distinguished clinically or dermoscopically, biopsy is mandatory.
4.5.11 Spots
Discrete pigmented spots within the nail plate carry diagnostic significance based on their color:
- Yellow spots: A well-demarcated, structureless, round to ovoid yellow spot is observed in subungual exostosis, caused by pressure from the underlying bone pressing on the nail bed.
- Red spots: Structureless red spots are associated with amelanotic melanoma and pyogenic granuloma. They differ from blood spots by their red color and regular ovoid/round shape (blood spots have a fibrillar distal aspect).
- Purple-blue spots: Associated with blue nevus of the nail unit or glomus cell tumor. In glomus tumors, pressure of the dermatoscope on the nail plate may trigger characteristic "electric" pain.
Check Your Understanding
What does the term 'micro-Hutchinson sign' mean, and what is its diagnostic significance?
The micro-Hutchinson sign refers to pigmentation visible only with dermoscopy at the proximal nail fold (cuticle area), not visible to the naked eye. It suggests that melanocytes producing the longitudinal melanonychia are extending beyond the nail matrix into the proximal nail fold. It is a concerning finding that raises suspicion for subungual melanoma.
Clinical Scenario
A 55-year-old man presents with a dark longitudinal band on his right thumbnail that has been widening over the past year. Dermoscopy of the nail plate reveals a brown-to-black band with lines of irregular thickness, spacing, and color intensity (irregular pattern). The proximal nail fold shows faint pigmentation visible only under dermoscopy (micro-Hutchinson sign). The band width is approximately 5 mm.
What is the clinical significance of the micro-Hutchinson sign, and what is the next step?
Subungual melanoma (nail apparatus melanoma)
The micro-Hutchinson sign -- periungual pigmentation visible only with dermoscopy at the proximal nail fold -- indicates that melanocytes producing the longitudinal melanonychia are extending beyond the nail matrix into the surrounding skin. This is a key dermoscopic indicator of nail apparatus melanoma. Combined with the irregular pattern (lines of variable color, thickness, spacing, and disrupted parallelism) and the widening band, the clinical picture is highly suspicious for melanoma. A nail matrix biopsy is mandatory. The irregular pattern on nail plate dermoscopy corresponds to disordered melanocyte proliferation within the nail matrix, in contrast to the regular pattern (uniform lines) seen in benign nail matrix nevi.
4.6 Diagnostic Approach to Nail Pigmentations
4.6.1 Step 1: Melanocytic versus Nonmelanocytic
The first goal is to determine whether the pigmentation is due to a melanocytic proliferation, a melanocytic activation, or a nonmelanocytic process. In most cases, clinical inspection and dermoscopy provide sufficient information to differentiate these entities.
Key distinguishing features:
- Melanin inclusions (pinpoint granules <0.1 mm in diameter visible with dermoscopy) within the melanonychia striata are associated with melanocytic lesions.
- Nonmelanocytic patterns include the globular/filamentous pattern of subungual hemorrhage and the homogeneous pigmentation without melanin granules seen in fungal infections.
4.6.2 Step 2: Gray versus Brown Background Color
- Gray band: Suggests melanocytic activation without hyperplasia (lentigo, drug-induced, ethnic pigmentation, lentiginoses, inflammatory, traumatic).
- Brown band: Suggests melanocytic hyperplasia or proliferation (nevus or melanoma). Proceed to Step 3.
4.6.3 Step 3: Regular versus Irregular Pattern
Within brown-pigmented bands, assess the micro-lines:
- Regular pattern (uniform color, thickness, spacing, parallelism): Favors nevus.
- Irregular pattern (variable color, thickness, spacing, disrupted parallelism): Favors melanoma. Biopsy is indicated.
Clinical Scenario
A 12-year-old girl is brought in by her parents for a brown longitudinal band on her left index fingernail that has been present since age 5. Dermoscopy reveals a 3 mm wide band with a brown background and regular, parallel lines of uniform color, thickness, and spacing. No micro-Hutchinson sign is seen. The free-edge dermoscopy shows pigment in the lower (ventral) nail plate.
What is the likely diagnosis, and how does free-edge dermoscopy help localize the melanocytic source?
Nail matrix nevus
The regular pattern -- parallel lines of uniform color, thickness, and spacing on a brown background -- is the dermoscopic hallmark of a benign nail matrix nevus. In children, longitudinal melanonychia is most commonly caused by melanocytic nevi, and the regular pattern is highly reassuring. Free-edge dermoscopy provides additional information: pigment localized to the lower (ventral) portion of the free edge indicates origin from the distal nail matrix, while pigment in the upper (dorsal) portion indicates proximal matrix origin. A distal matrix origin (as in this case) is favorable because distal matrix biopsies are less likely to cause permanent nail dystrophy. Given the patient's age and the entirely regular dermoscopic pattern, observation with serial photography is appropriate rather than immediate biopsy.
4.7 Nail Tumors
4.7.1 Nail Unit Lentigo
Lentigo and lentiginoses (Laugier-Hunziker, Peutz-Jeghers, Carney complex) usually affect multiple nails. Dermoscopy shows gray band-like pigmentation. Examination of palms, soles, and mucous membranes can confirm the diagnosis and obviate biopsy. New pigmented bands may develop over time.
4.7.2 Nevi of the Nail Matrix
Acquired Nevi
Characterized by brown background coloration and regular pattern of longitudinal micro-lines. The degree of pigmentation depends on the patient's skin type.
Congenital Nevi (CMN)
- Present at birth or manifest within the first few years of life (tardive congenital nevi).
- Clinical morphology is often concerning for melanoma due to dark pigmentation and frequent involvement of surrounding skin.
- Dermoscopic features that overlap with SUM in adults include: triangular shape of the melanonychia striata, pigment on the cuticle and hyponychium, and nail plate softening or erosion.
- Hyponychium pigment in CMN usually shows a parallel furrow pattern or a serrated/fibrillar pattern crossing perpendicular to the dermatoglyphics.
- Reassuring features: Young age (before age 5) and stability over time. The occurrence of SUM in children is extremely low.
- Long-term digital monitoring is recommended.
Blue Nevus
Rare. Manifests as a blue spot located near the proximal portion of the nail plate. Remains stable over time.
4.7.3 Melanoma of the Nail Matrix
Pigmented Variant
In cases of melanonychia striata developing after puberty, melanoma must always be in the differential diagnosis.
Clinical signs associated with melanoma:
- Adult onset
- Involvement of a single digit
- Dynamic lesion with changes over time
- Triangular shape of the band (indicating rapid growth)
- Polychromia
- Hutchinson sign
Dermoscopic features of nail melanoma:
- Multiple shades of brown and black within the band
- Irregular pattern of micro-lines (variable color, thickness, spacing, disrupted parallelism)
- Brown to black dots and globules in association with the longitudinal lines
- Micro-Hutchinson sign: Dermoscopic visualization of periungual pigment invisible to the naked eye
- Pigmentation on the hyponychium with a parallel ridge pattern
- Diffuse pigmentation with multiple shades of brown on lateral and proximal paronychial areas
Epidemiology:
- Same incidence across all races; however, it is one of the more frequent melanoma subtypes in Black and Asian populations
- Usually diagnosed in middle-aged to elderly individuals
- Most frequently affected digits: index finger, thumb, and hallux
- Approximately 50% of patients recall preceding trauma to the involved digit
- Advanced stages show nail plate dystrophy or loss due to progressive matrix destruction
Amelanotic Melanoma
- Early-stage amelanotic melanoma is extremely difficult to diagnose, appearing as a faint to almost imperceptible erythronychia.
- As it grows, it causes nail dystrophy, partial or complete erosion of the nail plate, and may reveal irregular vessels, exophytic growth, ulceration, or a bleeding tumor on the nail bed.
- Differential diagnoses: pyogenic granuloma, trauma-induced nail deformities, lichen planus, pustular psoriasis, tuberculosis, and Orf.
4.7.4 Benign Epithelial Tumors
Onychomatricoma
- Benign tumor of the nail matrix exhibiting nail dystrophy and a well-demarcated whitish-to-yellowish band with splinter hemorrhages.
- Associated with nail thickening.
- Free-edge dermoscopy: Characteristic honeycomb-like punctuations (almost pathognomonic).
- Intraoperative dermoscopy: Multiple hyperbolic crypts on the ventral plate ("Sagrada Familia sign"), proximal digitations, and mirror sign.
- Differential diagnosis: SCC.
Onychopapilloma
- Benign neoplasm of the nail bed and distal matrix.
- Presents as localized longitudinal erythronychia or leuko-xanthonychia.
- Splinter hemorrhages are common.
- Distal examination: Focal subungual hyperkeratosis with V-shaped distal onycholysis.
4.7.5 Malignant Epithelial Tumors
Squamous Cell Carcinoma (SCC) / Bowen Disease
- Usually involves a single digit; rarely multiple.
- Nail plate shows white-to-yellow longitudinal discoloration; pigmented cases are not uncommon (grayish rather than brown/black).
- Other features: splinter hemorrhages, polychromia, focal subungual hyperkeratosis, distal subungual onycholysis, triangular-shaped lunula.
- Periungual SCC dermoscopy: Scale, glomerular vessels, white circles, or tiny gray-to-brown dots.
4.7.6 Other Nail Tumors
Glomus Cell Tumor
- Benign hamartoma of the glomus body (specialized arteriovenous anastomosis in the stratum reticularis, involved in thermoregulation).
- Represents 1-5% of soft tissue tumors of the hand; most commonly subungual.
- Typically presents in young adults (20-40 years) as small, painful, reddish subungual tumefactions. Pain is increased by pressure and cold.
- Dermoscopy: Structureless purple or blue spot under the nail plate; may also reveal ramifying vessels within a red-blue tumor.
- Clinical tests:
- Love test: Pain reproduced by pinpoint pressure on the affected fingertip (sensitivity 100%, specificity 78%).
- Hildreth test: Tenderness disappears with digital tourniquet application (sensitivity 77.4%, specificity 100%).
- Cold sensitivity test: Pain elicited by cold exposure (sensitivity 100%, specificity 100%).
- Treatment: Complete surgical removal. Intraoperative dermoscopy can help delineate tumor margins.
Subungual Exostosis
- Isolated, acquired, slow-growing, benign osteochondral outgrowth of the dorsal distal phalanx.
- Most common in young adults, localized to the first right hallux.
- Caused by acute trauma, repeated chronic trauma, or chronic infection.
- Dermoscopy: Vascular ectasia (most frequent finding), hyperkeratosis, onycholysis, ulceration. A well-delineated yellow spot becomes more conspicuous when pressure is applied with the dermatoscope faceplate.
Check Your Understanding
How does dermoscopy help differentiate subungual melanoma from benign longitudinal melanonychia?
Benign longitudinal melanonychia shows regular, parallel brown lines of uniform color, width, and spacing. Subungual melanoma shows irregular lines with variation in color (brown, black, gray), width, spacing, and parallelism. Additional clues include Hutchinson or micro-Hutchinson sign, nail dystrophy, and loss of parallel line organization. The ABCDEF rule for nail melanoma provides a structured approach.
Key Takeaways
- Subungual hemorrhage appears as globules of red-brown to purple-black color that migrate distally with nail growth, distinguishing it from fixed melanonychia.
- Nail psoriasis shows pitting, oil-drop discoloration, splinter hemorrhages, and subungual hyperkeratosis, all identifiable with dermoscopy of the nail plate.
- Onychomycosis produces a spiked or jagged proximal border of discoloration visible under dermoscopy, contrasting with the smooth proximal border of melanonychia.
4.8 Inflammations, Infections, and Trauma-Induced Pigmentations
4.8.1 Subungual Hemorrhage (Hematoma)
A collection of blood between the nail bed and the nail plate, resulting from acute injury or repetitive minor trauma. Most frequently involves the thumb and hallux.
Clinical appearance: Well-circumscribed dots or blotches of red to maroon to black pigmentation. Can raise clinical concern for melanoma.
Dermoscopic features:
- Most frequent color: Purple-black.
- Acute lesions: Pink, purple, and red predominate.
- Older lesions: Darker colors -- purple-black, red-black, brown-black.
- Proximal pattern: Homogeneous blotch or globules.
- Distal pattern: Filamentous (due to capillary action).
- Migration: Blood migrates distally with nail plate growth.
Critical evaluation points:
- Subungual hemorrhage can coexist with melanoma. The nail must always be evaluated for the presence or absence of a pigmented band.
- The hyponychium and paronychial area should be evaluated for pigment.
- Subungual hemorrhage with a pigmented band or Hutchinson sign warrants biopsy.
- Subungual hemorrhage without a pigmented band or Hutchinson sign can be confirmed by follow-up (blood will migrate distally and eventually disappear).
4.8.2 Onychotillomania
In skin types IIIb-V, post-inflammatory or post-traumatic pigmentation can occur on the nails. Symmetrical pigmentation of the fifth toenail in women due to tight-fitting shoes is a classic example. Self-inflicted repetitive trauma causes longitudinal pigmentation. Dermoscopy reveals a gray band.
4.8.3 Warts
Periungual warts caused by HPV show dermoscopic features of thrombosed capillaries (black dots and short lines) over a yellow structureless background. Subungual warts are impossible to differentiate dermoscopically from SCC.
4.8.4 Fungal Infections (Onychomycosis)
Dermoscopy helps differentiate onychomycosis from traumatic onycholysis:
- Onychomycosis: Jagged proximal edge with spikes on the onycholytic area and longitudinal streaks. Homogeneous pigmentation without identifiable melanin granules in the nail plate.
- Traumatic onycholysis: Proximal linear edge without spikes.
4.8.5 Ethnic-Type Pigmentation
Often involves multiple digits. Predominates on the dominant hand (right hand in right-handed patients, left hand in left-handed patients), suggesting repetitive trauma-induced melanocytic activation. Dermoscopy reveals grayish pigmentation.
4.8.6 Drug-Induced Pigmentation
Many drugs induce nail plate pigmentation, including hydroxyurea, bleomycin, minocycline, and azidothymidine (AZT). Dermoscopic features resemble lentiginoses: polydactylic gray longitudinal bands.
4.8.7 Alopecia Areata
Associated with trachyonychia, where the nail plate shows multiple fine, superficial longitudinal fissures covered by thin scales. The "shiny" variety shows superficial ridging and a myriad of small geometrical pits.
4.8.8 Lichen Planus
Nails are thinned with longitudinal ridging and fissuring with distal splitting. Dermoscopy shows multiple deep longitudinal fissures reaching the distal part of the nail and partial absence of the nail plate. Useful for follow-up and evaluating treatment response.
4.8.9 Nail Psoriasis
Usually associated with skin psoriasis. Pits consisting of punctate nail plate depressions are easily seen with dermoscopy.
4.9 Which Lesions Should Be Biopsied?
Any lesion with an irregular dermoscopic pattern should be biopsied. The following situations should alert the clinician to the possibility of malignancy:
- An isolated pigmented band on a single digit that develops during the fourth to sixth decade of life.
- Nail pigmentation that develops abruptly in a previously normal nail plate.
- Pigmentation that suddenly becomes darker or larger.
- Acquired pigmentation of the thumb, index finger, or large toe.
- Pigmentation that develops after digital trauma in which subungual hematoma has been ruled out.
- Nail pigmentation associated with nail dystrophy, including partial nail destruction or absence of the nail plate.
- Pigmentation of the periungual skin (including lateral nail folds, cuticle, or hyponychium) -- Hutchinson sign.
Biopsy considerations: Because of the dendritic morphology and suprabasal location of nail matrix melanocytes, differentiating in situ melanoma from a nevus on a partial biopsy (punch biopsy) can be very difficult. Whenever possible, a complete longitudinal excision or broad shave biopsy of the nail matrix associated with the band is preferable.
Check Your Understanding
According to dermoscopic guidelines, when should a nail biopsy be performed for longitudinal melanonychia?
Biopsy is indicated for: single-digit longitudinal melanonychia with irregular dermoscopic features (non-parallel lines, variable colors, variable spacing), new-onset melanonychia in adults over 50, rapid change in a previously stable band, width greater than 3 mm, Hutchinson or micro-Hutchinson sign, and triangular shape of the pigmented band (wider at the proximal end).
Key Takeaways
- The melanonychia algorithm: assess band features (width >3 mm, color heterogeneity, irregular spacing) and clinical context (age >50, single digit, dominant hand) to determine biopsy need.
- Children commonly develop melanonychia from nail matrix nevi that show regular brown bands; monitoring is preferred over biopsy for typical pediatric presentations.
- Any melanonychia with Hutchinson sign (clinically visible periungual pigmentation), rapid band widening, or nail plate destruction requires urgent biopsy to exclude melanoma.
5. Melanonychia Evaluation Algorithm
flowchart TD
A[Pigmented Nail<br/>Band Identified] --> B{Step 1: Melanocytic<br/>or Nonmelanocytic?}
B -->|Nonmelanocytic| C[Hemorrhage, Fungal,<br/>Warts, SCC --<br/>Manage Accordingly]
B -->|Melanocytic| D{Step 2: Background<br/>Color?}
D -->|Gray Band| E[Melanocytic Activation<br/>Lentigo, Ethnic,<br/>Drug-Induced]
D -->|Brown Band| F{Step 3: Micro-Line<br/>Pattern?}
E --> G[Usually Benign<br/>-- Monitor]
F -->|Regular: Uniform color,<br/>thickness, spacing| H[Likely Nevus --<br/>Monitor / Photograph]
F -->|Irregular: Variable color,<br/>thickness, disrupted<br/>parallelism| I[Melanoma Suspected<br/>-- BIOPSY Indicated]
flowchart TD
A[ABCDEF Rule<br/>for Nail Melanoma] --> B{A: Age 50-70?<br/>High-risk ethnicity?}
B --> C{B: Band width >= 3 mm?<br/>Irregular borders?}
C --> D{C: Rapid change<br/>in morphology?}
D --> E{D: Dominant digit?<br/>Thumb, hallux, index?}
E --> F{E: Extension -- Hutchinson<br/>sign present?}
F --> G{F: Family/personal<br/>history of melanoma?}
G -->|Multiple features<br/>present| H[High Suspicion --<br/>Nail Matrix Biopsy]
G -->|Few or no<br/>features| I[Lower Suspicion --<br/>Monitor with<br/>Photography]
The following text-based flowchart summarizes the stepwise approach to evaluating a pigmented nail band:
Text version of algorithm
PIGMENTED NAIL BAND IDENTIFIED
|
v
[Step 1] Is this a melanocytic or nonmelanocytic process?
|
+-----+-----+
| |
v v
NONMELANOCYTIC MELANOCYTIC
(e.g., subungual |
hemorrhage, |
fungal infection, |
warts, SCC) |
| v
v [Step 2] What is the background color?
Manage |
accordingly +-----+-----+
| |
v v
GRAY BROWN
band band
| |
v v
Melanocytic Melanocytic
ACTIVATION PROLIFERATION
| |
v v
Usually benign [Step 3] What is the micro-line pattern?
(lentigo, |
ethnic, +-----+-----+
drug-induced, | |
lentiginoses) v v
| REGULAR IRREGULAR
v pattern pattern
Monitor | |
v v
NEVUS MELANOMA
(likely) suspected
| |
v v
Monitor or BIOPSY
photograph indicated
(age-dependent)
Additional considerations at each step:
- If subungual hemorrhage: confirm with follow-up
(blood migrates distally with nail growth)
- If gray band on single digit: rare but consider
early melanoma in situ or Bowen disease
- If brown band in child/adolescent: consider
congenital nevus (reassuring if stable)
- Always assess: Hutchinson sign, micro-Hutchinson
sign, and hyponychium for parallel ridge pattern
The ABCDEF Rule for Nail Melanoma
The ABCDEF rule, as applied to melanonychia evaluation, provides a structured mnemonic for identifying features that warrant biopsy:
| Letter | Feature | Details |
|---|---|---|
| A | Age | Peak incidence 5th-7th decade; also African American, Asian, Native American heritage (higher relative incidence of acral melanoma) |
| B | Band (brown-black) | Width >=3 mm; irregular/blurred borders |
| C | Change | Rapid change in band morphology (width, color) despite absence of identifiable cause |
| D | Digit | Thumb > hallux > index finger; dominant hand involvement |
| E | Extension | Hutchinson sign -- pigment extending to proximal or lateral nail fold (cuticle, paronychium, hyponychium) |
| F | Family/personal history | History of melanoma or dysplastic nevus syndrome; also consider atypical mole syndrome |
6. Benign vs. Malignant Melanonychia Table
| Feature | Benign (Nevus/Activation) | Malignant (Melanoma) |
|---|---|---|
| Background color | Brown (nevus) or gray (activation) | Brown, often with multiple shades |
| Micro-line color | Uniform -- similar shades of brown | Variable -- white, light brown, dark brown, gray, black |
| Micro-line thickness | Uniform throughout | Variable, with thick and thin lines intermixed |
| Micro-line spacing | Organized, even, symmetric | Disorganized, uneven, asymmetric |
| Parallelism | Lines parallel from proximal to distal | Lines may merge, converge, or end abruptly (disruption of parallelism) |
| Band shape | Parallel borders (rectangular) | Triangular (wider proximally than distally = rapid growth) |
| Number of digits | Often multiple (ethnic, drug, lentiginoses) | Usually single digit |
| Hutchinson sign | Absent (or pseudo-Hutchinson) | Present (true Hutchinson or micro-Hutchinson sign) |
| Periungual pigmentation | Pseudo-Hutchinson (translucent cuticle); congenital nevi may show furrow pattern on hyponychium | True pigmentation of cuticle, paronychium, or hyponychium with parallel ridge pattern |
| Nail plate | Intact | May show dystrophy, erosion, or absence in advanced disease |
| Associated findings | None specific | Blood spots, splinter hemorrhages, dots/globules, polychromia |
| Age of onset | Congenital or childhood (nevus); any age (activation) | Adult onset, especially 4th-7th decade |
| Typical digits | Any; often multiple | Thumb, index finger, hallux |
| Evolution | Stable or very slow change | Progressive darkening, widening, change over months |
7. Nail Dermoscopy Features Reference Table
| Dermoscopic Feature | Appearance | Associated Conditions |
|---|---|---|
| Blood spots | Round proximal edge, filamentous distal edge; purple-red to black-brown | Subungual hemorrhage (trauma, anticoagulation); rarely underlying tumor |
| Brown background | Longitudinal band, light-dark brown | Melanocytic proliferation: nevus, melanoma |
| Gray background | Longitudinal band, grayish | Melanocytic activation: lentigo, ethnic, drug-induced, HIV, inflammatory, lentiginoses |
| Regular micro-lines | Uniform color, thickness, spacing; parallel; full length | Nail matrix nevus |
| Irregular micro-lines | Variable color/thickness/spacing; disrupted parallelism | Nail matrix melanoma |
| Melanin inclusions | Pinpoint granules <0.1 mm | Melanocytic lesion (nevus or melanoma) |
| Hutchinson sign | True pigmentation of cuticle | Melanoma (highly suggestive); congenital nevus |
| Micro-Hutchinson sign | Pigment in cuticle visible only with dermoscopy | Melanoma; ethnic pigmentation; congenital nevus |
| Pseudo-Hutchinson sign | Nail plate pigment seen through translucent cuticle | No diagnostic significance |
| Atypical Hutchinson sign | Pigment on paronychium or hyponychium | If parallel ridge pattern or irregular diffuse pigment: suspect melanoma |
| Triangular band shape | Band wider proximally, narrower distally | Rapidly growing melanoma; congenital nevus (in children) |
| Polychromia | >=4 colors (black, red, blue, white, yellow, brown, gray, purple) | SCC, amelanotic melanoma |
| Leuko-xanthonychia | White-yellow longitudinal band | Epithelial tumors (onychomatricoma, onychopapilloma, SCC) |
| Splinter hemorrhages | Longitudinal thin lines under nail plate | Systemic disease (multiple nails); epithelial tumors (single nail); amelanotic melanoma (random + erythronychia) |
| Atypical vessels | Irregular caliber, >=3 vessel types, milky-red areas | Advanced malignant tumors (SCC, amelanotic melanoma) |
| Yellow spot | Well-demarcated, round/ovoid, structureless | Subungual exostosis |
| Red spot | Structureless, ovoid/round | Amelanotic melanoma, pyogenic granuloma |
| Purple-blue spot | Structureless, through nail plate | Blue nevus of nail unit; glomus cell tumor |
| Honeycomb-like pitting (free edge) | Round openings in thickened nail plate | Onychomatricoma (nearly pathognomonic) |
| V-shaped distal onycholysis | Triangular erosion + focal hyperkeratosis | Onychopapilloma |
| Jagged proximal edge with spikes | Irregular proximal margin of onycholysis | Onychomycosis |
| Linear proximal edge (no spikes) | Smooth proximal margin of onycholysis | Traumatic onycholysis |
| Thrombosed capillaries | Black dots/short lines on yellow background | Periungual warts |
| Deep longitudinal fissures | Full-length fissures with nail thinning | Lichen planus |
| Punctate pits | Small nail plate depressions | Nail psoriasis |
| Geometrical pits with ridging | Superficial ridging + small pits ("shiny" variety) | Alopecia areata (trachyonychia) |
8. Clinical Pearls
Use gel, not alcohol. Ultrasound gel or clear gel-based hand sanitizer is the preferred immersion medium for nail dermoscopy because its viscosity keeps it in place on the curved nail surface and fills concavities.
Always examine the free edge. Free-edge dermoscopy localizes the melanocytic lesion to the proximal or distal nail matrix, directly guiding biopsy placement. It also reveals the honeycomb pattern of onychomatricoma and the subungual hyperkeratosis of SCC or onychopapilloma.
Gray = activation, Brown = proliferation. This simple color-based distinction at the first step of the algorithm separates the majority of benign melanocytic activations (lentigo, drug-induced, ethnic, etc.) from the melanocytic proliferations (nevi and melanomas) that require further pattern analysis.
A gray band on multiple digits is almost always benign. While a single gray band on a single digit may rarely represent early melanoma in situ or Bowen disease, polydactylic gray bands are reassuring.
Beware the "pseudo" in pseudo-Hutchinson sign. Seeing pigment "in" the cuticle on dermoscopy does not necessarily mean Hutchinson sign. If the cuticle is translucent, nail plate pigment beneath it creates a pseudo-Hutchinson sign of no diagnostic significance.
Micro-Hutchinson sign is not melanoma-specific. While associated with melanoma, micro-Hutchinson sign can also occur in ethnic-type pigmentation and congenital nevi. Always integrate the full clinical and dermoscopic picture.
Subungual hemorrhage moves slower than the nail plate. Blood migrates distally at approximately half the rate of nail plate growth. If blood is present throughout the nail, re-examination in 3-4 months is mandatory to verify that a normal proximal nail plate is growing in.
Subungual hemorrhage can coexist with melanoma. Always search for a pigmented band and Hutchinson sign even when blood spots are present. The presence of hemorrhage does not exclude an underlying malignancy.
Children get dark nails from congenital nevi, not melanoma. Congenital nevi involving the nail unit can mimic melanoma due to dark pigmentation, triangular band shape, and periungual pigment. However, SUM in children is extraordinarily rare. Young age and stability are reassuring.
The "ABCDEF" rule is a screening tool, not a definitive diagnosis. It helps systematize the decision to biopsy but does not replace dermoscopic pattern analysis. Any irregular dermoscopic pattern warrants biopsy regardless of ABCDEF score.
Amelanotic melanoma is the great mimicker. It can present as faint erythronychia, nail dystrophy, or a bleeding nodule. Consider melanoma in any unexplained nail bed lesion with atypical vessels, milky-red areas, or nail plate erosion, especially when differential diagnoses include pyogenic granuloma.
Prefer longitudinal excision over punch biopsy. The dendritic morphology and suprabasal location of nail matrix melanocytes make in situ melanoma extremely difficult to distinguish from nevus on a small punch biopsy. A complete longitudinal excision or broad shave biopsy of the involved matrix segment is preferable.
Pressure test for glomus tumors. When a purple-blue spot is seen under the nail plate, pressing the dermatoscope against the nail may elicit the characteristic sharp "electric" pain of a glomus cell tumor -- effectively using the dermoscope as a diagnostic test.
Subungual warts vs. SCC -- biopsy is the answer. Subungual warts are dermoscopically indistinguishable from SCC. When keratotic subungual lesions are present, biopsy is necessary.
Clinical Vignettes
Clinical Scenario A 55-year-old woman presents with a 3 mm wide longitudinal brown band on her right thumbnail, widening over 8 months. Dermoscopy reveals brown micro-lines with variable thickness, uneven spacing, and areas where lines merge. The band is wider proximally (triangular shape). Free-edge dermoscopy shows distal matrix localization.
What is the most likely diagnosis?
Diagnosis: Subungual melanoma.
Irregular micro-lines with variable width, uneven spacing, and line merging are the hallmark of subungual melanoma. The triangular band shape indicates active matrix melanocyte proliferation. Clinical Pearl 3: brown = proliferation (vs. gray = activation). Clinical Pearl 12: prefer longitudinal excision over punch biopsy for accurate histopathologic diagnosis.
Clinical Scenario A 30-year-old man of African descent presents with light gray-brown longitudinal bands on multiple fingernails bilaterally, present since childhood. Dermoscopy reveals thin, regular, parallel gray lines with uniform spacing across all affected nails. No Hutchinson sign or nail dystrophy.
What is the most likely diagnosis?
Diagnosis: Ethnic (racial) melanonychia.
Clinical Pearl 3: gray = activation, placing this in the benign category. Clinical Pearl 4: gray bands on multiple digits are almost always benign. Bilateral polydactylic distribution, childhood onset, and uniform regular pattern are characteristic. No biopsy is indicated.
Clinical Scenario A 48-year-old woman presents with a dark longitudinal band on the left great toenail. She also reports occasional bleeding after trauma. Dermoscopy shows a broad brown band with irregular lines plus a reddish-brown globular area. Periungual pigmentation is visible on the cuticle, but the cuticle is translucent with nail plate pigment beneath.
What is the most likely diagnosis?
Diagnosis: Melanocytic lesion requiring biopsy -- hemorrhage does not exclude melanoma.
Clinical Pearl 8: subungual hemorrhage can coexist with melanoma. Always search for a pigmented band even when blood is present. Clinical Pearl 5: the pigment "in" the cuticle here is pseudo-Hutchinson sign (nail plate pigment visible through translucent cuticle). However, the irregular micro-lines in the brown band independently warrant biopsy.
10. Cross-References
| Topic | Reference |
|---|---|
| Nail anatomy and dermoscopic technique | Ch. 11d, pp. 269-270 |
| Blood spots (subungual hemorrhage semiology) | Ch. 11d, pp. 270-271 |
| Background pigmentation (brown vs. gray) | Ch. 11d, pp. 271-272 |
| Regular and irregular micro-line patterns | Ch. 11d, pp. 272, 276 |
| Hutchinson sign and variants | Ch. 11d, pp. 272-273 |
| Longitudinal xantho-leukonychia | Ch. 11d, p. 273 |
| Splinter hemorrhages | Ch. 11d, pp. 273-274 |
| Polychromia | Ch. 11d, p. 274 |
| Atypical vessels | Ch. 11d, p. 274 |
| Spots (yellow, red, purple-blue) | Ch. 11d, pp. 274-275 |
| Diagnostic algorithm for nail pigmentations | Ch. 11d, pp. 275-276 |
| Gray-pigmented bands | Ch. 11d, pp. 275-276 |
| Brown-pigmented bands (regular vs. irregular) | Ch. 11d, pp. 276 |
| Nail unit lentigo | Ch. 11d, p. 276 |
| Nevi of the nail matrix (acquired, congenital, blue) | Ch. 11d, pp. 276-277 |
| Melanoma of the nail matrix (pigmented and amelanotic) | Ch. 11d, p. 277 |
| Onychomatricoma | Ch. 11d, p. 277 |
| Onychopapilloma | Ch. 11d, p. 277 |
| Squamous cell carcinoma | Ch. 11d, p. 277 |
| Glomus cell tumor | Ch. 11d, pp. 277-278 |
| Subungual exostosis | Ch. 11d, p. 278 |
| Subungual hemorrhage (detailed) | Ch. 11d, p. 278 |
| Onychotillomania | Ch. 11d, p. 279 |
| Warts | Ch. 11d, p. 279 |
| Onychomycosis | Ch. 11d, p. 279 |
| Ethnic/drug-induced pigmentation | Ch. 11d, p. 279 |
| Alopecia areata, lichen planus, psoriasis | Ch. 11d, p. 279 |
| Biopsy indications | Ch. 11d, p. 279 |
| Acral dermoscopy patterns (parallel ridge, parallel furrow) | Ch. 11b (Acral Volar Skin) |
11. Related Modules
- Module 01: Introduction and Principles of Dermoscopy -- Foundational dermoscopic technique and equipment knowledge required for nail examination.
- Module 03: Pattern Analysis -- Core vocabulary for describing colors, structures, and patterns used throughout nail dermoscopy.
- Module 04: Two-Step Algorithm -- Framework for the melanocytic vs. nonmelanocytic distinction that forms Step 1 of the nail pigmentation algorithm.
- Module 24: Acral Lentiginous Melanoma (ALM) -- Closely related module covering melanoma of acral sites. Shared concepts include the parallel ridge pattern, parallel furrow pattern, and the ABCDEF rule. Nail melanoma (subungual melanoma) is a subtype of acral melanoma, and periungual pigmentation patterns follow volar skin dermoscopy principles. Understanding ALM dermoscopy is essential for evaluating atypical Hutchinson sign and hyponychium pigmentation.
- Module 09: Basal Cell Carcinoma -- Background on vascular patterns (arborizing vessels) that may be encountered in differential diagnosis of nail bed tumors.
- Module 11: SCC Spectrum -- Squamous cell carcinoma is an important differential for nail pigmentation, particularly Bowen disease affecting the nail unit. Relevant dermoscopic features (glomerular vessels, scale, polychromia) are discussed.
- Module 13: Vascular Lesions -- Provides context for understanding atypical vascular patterns, milky-red areas, and the vascular features of glomus cell tumors and pyogenic granuloma.