Module 34: Special Locations -- Hair and Scalp (Trichoscopy)

Trichoscopy (also called hair and scalp dermoscopy or hair and scalp videodermatoscopy) is the application of dermoscopy to the examination of hair and scalp disorders. It is a noninvasive diagnostic method that has been shown to improve diagnostic capability beyond simple clinical inspection. Trichoscopy is valuable for:

• Diagnosis of hair and scalp disorders
• Evaluation of disease activity and staging
• Monitoring treatment efficacy
• Guiding biopsy site selection in scalp biopsy

Hand-held dermatoscopes provide standard 10-fold magnification and are sufficient for most trichoscopic diagnoses. Videodermatoscopes offer 20- to 1000-fold magnification and allow more precise measurements of structures such as hair shaft thickness, making them particularly useful for monitoring disease severity.

Interface solutions for nonpolarized light trichoscopy include:

• 90% isopropanol
• 70% ethanol
• Ultrasound gel
• Water

Dry dermoscopy (without interface fluid) may be preferable in some cases for improved visualization of scale.

A systematic trichoscopic examination should evaluate:

1. Hair shaft features: diameter, number per follicular unit, morphologic abnormalities
2. Follicular openings: presence, absence, and content (empty, yellow dots, black dots, white dots, red dots)
3. Perifollicular and interfollicular epidermis: pigmentation, scaling, erythema, fibrosis
4. Cutaneous microvasculature: vascular morphology and distribution
5. Exogenous materials: dyes, camouflage products, hairspray residues, ectoparasites

The most fundamental trichoscopic distinction is between scarring and nonscarring alopecia:

• Nonscarring alopecia: Follicular openings are preserved; the process is potentially reversible.
• Scarring (cicatricial) alopecia: Follicular openings are lost (white dots, confluence into areas devoid of ostia); the process results in permanent follicular destruction.

---

4.1.1 Hair Shaft Abnormalities

Hair shaft abnormalities may result from genetic conditions and/or exogenous factors affecting the integrity of the hair shaft. They can occur as localized or generalized disorders. Trichoscopy provides a rapid, noninvasive alternative to traditional microscopic examination of plucked hairs.

Broken hairs: Hair shafts fractured at or near the scalp surface, resulting in short, irregularly broken stumps. Seen in trichotillomania (at different lengths, reflecting repeated mechanical extraction), alopecia areata, and tinea capitis.

Exclamation mark hairs (exclamation point hairs, micro-exclamation mark hairs): Short hairs (1--2 mm on trichoscopy; 5--15 mm with unaided eye) with a thin, tapered proximal end and a thicker distal end, resembling an exclamation mark. They are specific for active alopecia areata and represent dystrophic anagen hairs undergoing premature termination.

Tapered hairs: Hairs that gradually thin toward the proximal end. Like exclamation mark hairs, they indicate active hair matrix damage and are a marker of active alopecia areata.

Comma hairs: Short, C-shaped hairs with a uniform thickness that have been fractured and curled. They are a dermatoscopic marker for tinea capitis (dermatophyte infection) and represent hairs invaded and weakened by fungal elements.

Corkscrew hairs: Tightly coiled, spiral-shaped hairs. Along with comma hairs, they are characteristic of tinea capitis and reflect fungal invasion of the hair shaft causing it to twist tightly.

Morse code-like hairs: Hairs with alternating thick and thin segments, creating a pattern reminiscent of Morse code. Observed in tinea capitis.

Zigzag hairs (Z-hairs): Hairs with angulated bends, creating a zigzag pattern. Seen in tinea capitis.

Flame hairs: Short, residual hair shaft remnants with wavy, flame-like morphology, resembling a flame rising from the follicular opening. They are a trichoscopy finding specific to trichotillomania and result from mechanical extraction causing the hair to fracture and splay.

Tulip hairs: Short hairs with a tulip-shaped dark tip resembling the flower. Characteristic of trichotillomania; they represent diagonally fractured short hair shafts where the dark tip creates a tulip-like appearance.

V-sign (V-shaped hairs): Two or more hair shafts emerging from a single follicular opening that are broken at the same length, forming a V shape. Specific to trichotillomania and reflect simultaneous mechanical fracture of multiple hairs within the same follicular unit.

Coiled hairs: Short hairs that curl upon themselves within or near the follicular opening. Seen in trichotillomania (resulting from mechanical trauma) and as pigtail hairs in regrowing alopecia areata.

Pigtail hairs: Short, newly regrowing hairs with a curled or coiled appearance, resembling a pigtail. Characteristic of hair regrowth in alopecia areata.

Hair powder: Fine, dust-like fragments of fractured hair shafts on the scalp surface. A trichoscopic finding of trichotillomania.

Longitudinally split short hairs: Short hairs with longitudinal splitting (trichoptilosis). Observed in trichotillomania and represent mechanical splitting of the hair shaft.

Trichoptilosis: Longitudinal splitting of the distal hair shaft (split ends). While common in normal hair weathering, its presence on short hairs near the scalp is abnormal and seen in trichotillomania.

Pohl-Pinkus constrictions: Localized narrowing(s) of the hair shaft, representing a transient insult to the hair matrix during anagen that caused temporary reduction in hair production. They are monilethrix-like but occur at irregular intervals.

Hair shaft diameter heterogeneity (anisotrichosis): The presence of hairs with markedly different calibers within the same scalp area. This is the hallmark trichoscopic finding of androgenetic alopecia, reflecting progressive hair follicle miniaturization. A diversity of more than 20% is considered diagnostic.

Vellus hairs: Fine, short, lightly pigmented or unpigmented hairs. An increased proportion indicates hair follicle miniaturization. Short vellus hairs are among the most common trichoscopic markers of alopecia areata; an increased number is also seen in androgenetic alopecia.

Upright regrowing hairs: Short, newly emerging terminal hairs growing perpendicular to the scalp surface. A sign of active hair regrowth, particularly in alopecia areata.

Block hairs and i-hairs: Short, fractured hair variants observed in tinea capitis.

Bent hairs: Hair shafts with abrupt angulations, seen in tinea capitis.

4.1.2 Congenital Hair Shaft Disorders

Monilethrix: An uncommon autosomal dominant condition producing hair shafts with a beaded appearance due to periodic thinning (uniform elliptical nodes with intermittent constrictions). Trichoscopy shows the "regularly bended ribbon sign" or "regularly twisted ribbon sign." Hairs tend to fracture at constriction sites.

Pili torti: Hair shafts that are flattened and twisted 180 degrees on their axis at varying intervals. On trichoscopy, regular twists along the long axis are visible at high magnification (videodermatoscopy), while hand-held dermoscopy reveals hair shafts bent at different angles at irregular intervals. May be hereditary (isolated trait, Menkes kinky hair syndrome, Bjornstad syndrome, ectodermal dysplasias) or acquired (around patches of lichen planopilaris, where inflammatory and fibrosing processes distort the follicle).

Pili canaliculi et trianguli (uncombable hair syndrome): Triangular hair shafts with longitudinal grooving. Requires videodermatoscopy at higher magnification (50-fold and above).

Pili annulati: Alternating light and dark banding in the hair shaft due to air-filled spaces between macro-fibrillar units of the hair cortex. Trichoscopy demonstrates hair shafts with regular light bands. Note: light/white in trichoscopy correlates with dark in conventional light microscopy, and vice versa. Affected hairs show increased fragility, especially when combined with androgenetic alopecia.

Trichorrhexis invaginata (bamboo hair): The marker of Netherton syndrome (autosomal recessive: bamboo hair + ichthyosis + atopic dermatitis). Trichoscopy shows characteristic nodes along the hair shaft (bamboo-like pattern) and hairs with "golf tee"-type endings.

Trichorrhexis nodosa: White knots with transverse fractures along the hair shaft, producing a brush-like fracturing pattern on trichoscopy. Most commonly a nonspecific finding related to excess external stress and hair weathering, though it may also be seen in genetic hair shaft disorders.

4.1.3 Follicular Structures (Dots)

Empty follicles (empty follicular ostia): Follicular openings devoid of hair. May represent the normal kenogen phase (physiologic rest between telogen hair extrusion and new anagen hair emergence). Visibly increased numbers are seen in telogen effluvium, androgenetic alopecia, and alopecia areata.

Yellow dots: Round or polycyclic, yellow to yellow-pink or yellow-brown, monomorphous but variably sized dots that are devoid of hair or contain dystrophic or vellus hairs. They correspond to dilated follicular infundibula containing sebaceous and/or keratinous material.

• Alopecia areata: Regularly distributed yellow dots are a typical finding (observed in 6--100% of cases, mean 62%). They predominate in chronic, nonactive disease and their presence is a marker of disease severity.
• Androgenetic alopecia: Yellow dots are present in 8--66% of patients. They are usually homogeneously colored (light yellow to dark brown), correspond to sebaceous material from intact glands associated with miniaturized follicles, and are significantly more numerous in the frontal area.
• Chronic telogen effluvium: Sparse yellow dots may be observed.
• Large yellow dots: Characteristic of discoid lupus erythematosus and folliculitis capitis abscedens et suffodiens. They correspond to excessive keratin accumulation causing follicular plugging.
• Three-dimensional soap bubble yellow dots: Specific for dissecting cellulitis when associated with dark dystrophic hairs.

Black dots (cadaverized hairs): Broken or destroyed pigmented hair shafts at the level of the scalp, appearing as small dark dots within follicular openings. They are seen in:

• Active alopecia areata (marker of disease activity, negative prognostic marker)
• Tinea capitis
• Trichotillomania
• Perifolliculitis abscedens et suffodiens
• Anagen alopecia after chemotherapy
• Black dots are NOT present in healthy individuals, androgenetic alopecia, or telogen effluvium.

White dots: Two distinct types have been identified:

• Classic (fibrotic) white dots: Result from follicular/perifollicular fibrosis. Usually >200 micrometers in diameter, evenly white in color with irregular borders. In advanced scarring alopecia, they become confluent, forming areas devoid of follicular ostia. They are the hallmark of scarring alopecia. Visibility is less conspicuous in light-skinned (phototype I) individuals due to reduced contrast.
• Pinpoint white dots: Small, regular white dots representing eccrine sweat gland openings. They are normally visible on sun-exposed areas and are more conspicuous in darker skin phototypes (Fitzpatrick V--VI). They may also be observed in frontal fibrosing alopecia, lichen planopilaris, alopecia areata, androgenetic alopecia, and central centrifugal cicatricial alopecia.

Red dots: Widened infundibula surrounded by dilated vessels and extravasated erythrocytes, with plugging by keratotic material. Characteristic of active discoid lupus erythematosus and considered a positive prognostic factor.

Blue-gray dots: Observed in discoid lupus erythematosus. Correspond to melanin incontinence with pigment deposition in the upper dermis.

4.1.4 Interfollicular and Perifollicular Structures

Brown (honeycomb) pigmentation: Homogeneous, mosaic, or contiguous brown rings in the interfollicular epidermis. Observed in:

• Normal dark skin phototypes
• Sun-exposed bald scalp in lighter phototypes
• Advanced androgenetic alopecia with unprotected sun exposure

Peripilar sign (brown perifollicular discoloration, perifollicular hyperpigmentation): A brown halo approximately 1 mm in diameter surrounding the follicular ostium. Initially linked to superficial perifollicular lymphocytic infiltrates in early androgenetic alopecia. However, it is a nonspecific sign present in various forms of hair loss and in normal skin (average 4.6% of follicular ostia in healthy females, but can be as high as 25%). A high percentage is considered suggestive of active telogen effluvium or "complicated androgenetic alopecia" and is associated with accelerated hair loss. In androgenetic alopecia, the peripilar sign predominates in the frontal scalp area.

Peripilar casts (perifollicular scaling): White scaling encircling the proximal hair shaft, forming a tubular or collar-like pattern around the follicle. White perifollicular scaling is a hallmark of lichen planopilaris.

Pink (milky-red) areas: Trichoscopic markers of early fibrosis in cicatricial alopecias.

White areas/patches: Correspond to late-stage fibrosing processes in scarring alopecia, representing complete replacement of normal tissue with scar.

Perifollicular erythema: Redness surrounding the follicular unit, indicating active inflammation. A key finding in lichen planopilaris and frontal fibrosing alopecia, serving as a marker of disease progression.

Loss of follicular ostia: The complete absence of visible follicular openings in an area. The cardinal feature of scarring alopecia. In some conditions (e.g., discoid lupus erythematosus), loss of follicular ostia may develop without the intermediate stage of visible white dots.

Scaling: Two types are recognized:

• Perifollicular scaling: White perifollicular scaling is characteristic of lichen planopilaris. Yellowish tubular scaling with collar formation is characteristic of folliculitis decalvans.
• Diffuse scaling: White diffuse scaling is seen in psoriasis, discoid lupus erythematosus, and contact dermatitis. Yellowish diffuse scaling is seen in seborrheic dermatitis, discoid lupus erythematosus, and ichthyosis.

Scaling severity may be graded semi-quantitatively from 0 (no scaling) to 4 (severe scaling in the whole field of vision).

4.1.5 Vascular Patterns

Simple red loops: Fine, red, hairpin-shaped structures that are regularly spaced. Represent normal capillary loop architecture, mainly seen in the occipital area.

Dotted vessels: Tiny red dots normally seen on the frontal area in normal skin.

Arborizing vessels: Tree-like terminal branching blood vessels.

• A few thin arborizing vessels may be present in normal skin.
• Multiple thin arborizing vessels are the hallmark of seborrheic dermatitis.
• Thick, focally arranged arborizing vessels are characteristic of discoid lupus erythematosus. This feature can lead to misdiagnosis as basal cell carcinoma.

Twisted red loops: Multiple, relatively evenly spaced, twisted loops in a homogeneous distribution.

• Characteristic of psoriasis.
• May occasionally be observed around affected follicles in folliculitis decalvans.

Very thin or absent blood vessels: May be observed in normal skin but are more common in diseases associated with systemic vasoconstriction (e.g., hyperthyroidism, scleroderma).

Coiled capillary loops: Numerous coiled loops observed around affected follicles, particularly in folliculitis decalvans.

Key Takeaways

• Trichoscopy (dermoscopy of the scalp and hair) evaluates hair shaft abnormalities, follicular patterns, perifollicular changes, and interfollicular features to diagnose alopecia.
• Black dots (cadaverized hairs broken at the scalp surface) and exclamation mark hairs (short, distally thicker, proximally thinner hairs) are hallmarks of alopecia areata.
• Perifollicular scales forming a collar around the follicular ostium are characteristic of frontal fibrosing alopecia and lichen planopilaris.

Clinical Scenario

A 28-year-old woman presents with a rapidly expanding patch of hair loss on her occipital scalp over the past 3 weeks. Trichoscopy reveals numerous black dots (cadaverized hairs broken at the scalp surface), exclamation mark hairs (short hairs that are thicker distally and thinner proximally), and regularly distributed yellow dots. No scarring or loss of follicular openings is observed.

What is the diagnosis, and what do the trichoscopic findings indicate about disease activity?

Active alopecia areata

The triad of black dots, exclamation mark hairs, and yellow dots is characteristic of alopecia areata. Black dots and exclamation mark hairs are markers of active disease -- they represent hairs that have been abruptly interrupted during anagen and fractured at or just below the scalp surface. Yellow dots are the most common trichoscopic finding in alopecia areata overall (seen in 6-100% of cases) and correspond to dilated follicular infundibula filled with keratinous material and sebum. The preservation of follicular openings confirms this is a nonscarring alopecia, distinguishing it from cicatricial alopecias. The combination of activity markers (black dots, exclamation mark hairs) in a patient with rapid onset indicates active disease that may benefit from early immunomodulatory therapy.

4.2.1 Alopecia Areata

Alopecia areata is a common hair loss condition characterized by acute onset of nonscarring hair loss, most commonly in sharply defined patches. Trichoscopy is valuable for diagnosis, staging, and monitoring.

Trichoscopic features of alopecia areata:

• Regularly distributed yellow dots (most common marker, 6--100% of cases; predominate in chronic, nonactive disease; marker of disease severity)
• Black dots (marker of active disease; negative prognostic marker)
• Exclamation mark hairs (specific for active disease)
• Broken hairs and tapered hairs (active disease markers)
• Short vellus hairs (among the most common markers; predominate in nonactive, long-standing disease)
• Upright regrowing hairs (sign of hair regrowth)
• Pigtail hairs (sign of hair regrowth)
• Empty follicular openings (increased compared to normal)

Alopecia areata incognita: An uncommon variety characterized by rapid diffuse shedding without typical discrete patches, mimicking telogen effluvium. Key trichoscopic clue: concomitant presence of yellow dots and short regrowing hairs in the terminal hair-bearing scalp. Hair loss is often more evident in the "androgen-dependent scalp area."

4.2.2 Androgenetic Alopecia

Androgenetic alopecia is the most common cause of hair loss in both women and men. Trichoscopic features reflect progressive follicular miniaturization.

Trichoscopic features of androgenetic alopecia:

• Hair shaft thickness heterogeneity (anisotrichosis) -- the hallmark finding; >20% diversity is diagnostic
• Brown perifollicular discoloration (peripilar sign) -- an early sign; corresponds to perifollicular lymphocytic infiltrates; negative prognostic marker; predominates in the frontal scalp
• Empty follicular openings (mainly as yellow dots) -- reflects increased frequency and longer duration of kenogen phase
• Yellow dots (present in 8--66%; irregularly distributed; higher in frontal area)
• Increased proportion of thin and vellus hairs
• Increased follicular units with one hair and decreased units with three hairs (compared to normal 1--4 hairs per unit)
• Honeycomb pigment pattern -- observed in advanced disease due to unprotected sun exposure
• Arborizing red blood vessels (telangiectasias) -- correlated with trichodynia (scalp pain/burning)

Frontal-occipital comparison: A predominance of trichoscopic abnormalities in the frontal area compared with the occipital area is highly indicative of androgenetic alopecia.

4.2.3 Telogen Effluvium

Telogen effluvium is characterized by diffuse, nonscarring hair shedding resulting from premature entry of anagen hairs into the telogen phase.

Trichoscopic features of telogen effluvium:

• Increased empty follicles -- the primary finding; reflects the physiologic lag phase (kenogen)
• Short regrowing hairs -- evidence of recovery
• Sparse yellow dots (in chronic telogen effluvium)
• Peripilar sign (brown perifollicular discoloration) -- when present, associated with accelerated hair loss
• Absence of black dots, exclamation mark hairs, and hair shaft thickness diversity (these features help distinguish from alopecia areata and androgenetic alopecia)

4.2.4 Trichotillomania

Trichotillomania is an impulse control disorder characterized by compulsive hair pulling. The most important differential diagnosis is alopecia areata; however, the two conditions may co-exist, posing a special diagnostic challenge.

Trichoscopic features of trichotillomania:

• Broken hairs at different lengths -- the hallmark; reflects repeated mechanical extraction at various times
• Coiled hairs -- short hairs curled upon themselves from trauma
• Flame hairs -- short, wavy, flame-like residual hair stumps
• V-sign -- two or more hairs broken at the same length from one follicle
• Tulip hairs -- short hairs with dark, tulip-shaped tips from diagonal fracture
• Trichoptilosis (longitudinally split short hairs) -- mechanical splitting
• Black dots -- pigmented hair remnants at scalp level
• Hair powder -- fine fragments of fractured hair shafts
• Empty hair follicles -- numerous, with coiled and broken hairs visible

4.2.5 Scarring Alopecias

Scarring (cicatricial) alopecias are characterized by permanent destruction of hair follicles. They are classified into primary (follicle is the primary target) and secondary (follicular damage incidental to surrounding events) forms. Trichoscopy is particularly helpful in differentiating the subtypes.

Universal trichoscopic features of scarring alopecia:

• Loss of follicular openings (cardinal feature)
• White dots (classic fibrotic white dots >200 micrometers)
• White areas (late fibrosis)
• Pink/milky-red areas (early fibrosis)

Lichen Planopilaris (LPP)

The most common cause of scarring alopecia in adults. Presents with pruritic central or multifocal patches, follicular hyperkeratosis, and erythema at the hair-bearing margin. Histopathology: lymphocytic scarring alopecia.

Trichoscopic features:

• White perifollicular scaling (peripilar casts) -- the hallmark finding
• Perifollicular erythema -- marker of active inflammation and progression
• White dots and loss of follicular ostia -- fibrotic change
• Acquired pili torti -- twisted hairs from follicular distortion by fibrosis
• Pink (milky-red) areas -- early fibrosis
• White areas -- late fibrosis

Frontal Fibrosing Alopecia (FFA)

A pattern distribution variant of lichen planopilaris affecting the frontal hairline. Shares trichoscopic features with LPP. Perifollicular erythema is a trichoscopy sign of progression. Loss of vellus hair at the hairline is a videodermatoscopic feature.

Discoid Lupus Erythematosus (DLE)

Presents as erythematous scaly plaques with follicular plugs, telangiectasias, and progressive central scarring. Histopathology: lymphocytic scarring alopecia.

Trichoscopic features:

• Loss of follicular ostia -- may develop without visible white dots
• Thick, focally arranged arborizing vessels -- can mimic basal cell carcinoma
• Follicular keratotic plugs (large yellow dots) -- excessive keratin accumulation
• Red dots -- widened infundibula with dilated vessels and extravasated erythrocytes; positive prognostic factor
• Blue-gray dots -- melanin incontinence
• Scalp atrophy with effaced or absent vascular loops
• White and yellowish diffuse scaling

Folliculitis Decalvans

Chronic, recurrent pustule-follicular scalp inflammation causing scarring. Usually central scalp, with exudative crusted areas and grouped follicular pustules. Histopathology: neutrophilic scarring alopecia.

Trichoscopic features:

• Severe scaling and crusting
• Pronounced hair tufting (5--20 hairs per follicular opening)
• Follicular pustules
• Numerous coiled capillary loops around affected follicles
• Yellowish perifollicular scaling with collar formation
• Loss of follicular ostia and white dots

Dissecting Cellulitis of the Scalp

Multiple firm, dome-shaped papules coalescing into plaques and nodules with abscesses and sinus tracts. Predominantly in men of African descent, ages 20--40. Histopathology: neutrophilic scarring alopecia.

Trichoscopic features:

• Yellow structureless areas
• Three-dimensional yellow dots (soap bubble appearance) with dark dystrophic hairs (specific)
• Black dots
• Perifollicular pustules

Pseudopelade of Brocq

Asymptomatic, noninflamed, ivory-white or flesh-colored patches. Lymphocytic scarring alopecia with selective destruction of hair follicles. Clinically and histologically indistinguishable from end-stage scarring alopecia of any origin (diagnosis of exclusion).

Trichoscopic features: Nonspecific -- loss of follicular ostia and occasionally white dots.

4.2.6 Tinea Capitis

Tinea capitis is mainly caused by Microsporum and Trichophyton species. Clinically characterized by hair loss areas with scaling, inflammation, or pustules. Trichoscopy allows rapid, noninvasive diagnosis.

Trichoscopic features of tinea capitis:

• Comma hairs -- C-shaped, short, fractured hairs (dermatoscopic marker for tinea capitis)
• Corkscrew hairs -- tightly coiled, spiral-shaped hairs
• Morse code-like hairs -- alternating thick and thin segments
• Zigzag hairs (Z-hairs) -- angulated, zigzag-shaped hairs
• Bent hairs -- hairs with abrupt angulations
• Block hairs and i-hairs -- short, fractured hair variants
• Broken hairs at the scalp surface
• Black dots

4.2.7 Pediculosis Capitis

Infestation by Pediculus humanus capitis (head louse). Trichoscopy allows visualization of nits (louse eggs) cemented to hair shafts and, at higher magnification, the ectoparasite itself with its elongated body, head structure, and three pairs of clawed legs.

4.2.8 Other Conditions

Follicular mucinosis: Follicular papules or plaques with hair loss. Trichoscopy shows follicular plugs of amorphous mucin material in dilated follicular ostia. May be primary (idiopathic) or secondary to mycosis fungoides.

Follicular filiform spicules: Rare paraneoplastic phenomenon associated with multiple myeloma. Multiple hyperkeratotic spicules on face, nose, and scalp.

Scalp psoriasis: White diffuse scaling with twisted red loops in homogeneous distribution.

Seborrheic dermatitis: Yellowish diffuse scaling with multiple thin arborizing vessels.

Check Your Understanding

What are the primary dermoscopic signs of androgenetic alopecia?

The primary signs include hair diameter diversity (more than 20% variation in shaft diameter), a predominance of follicular units with single hairs (loss of the normal 2-3 hairs per unit), yellow dots (empty follicles filled with sebum), perifollicular brown halo (perifollicular pigmentation), and white dots (fibrotic replacement of follicles in advanced stages).

Key Takeaways

• In scarring (cicatricial) alopecia, dermoscopy shows loss of follicular openings with white or ivory patches, indicating permanent follicular destruction.
• In non-scarring alopecia, follicular openings are preserved; the key features are hair shaft caliber variation (androgenetic), black dots/exclamation marks (alopecia areata), or broken hairs (tinea capitis).
• Yellow dots (dilated follicular infundibula filled with keratinous material) are seen in alopecia areata and androgenetic alopecia but are absent in scarring alopecias.

Clinical Scenario

A 52-year-old woman presents with progressive frontal hairline recession and thinning eyebrows over the past 2 years. Trichoscopy of the frontal hairline reveals perifollicular scales forming a collar around follicular ostia, loss of follicular openings in some areas replaced by ivory-white patches, and lonely hairs (single terminal hairs surrounded by fibrous tracts). No black dots or exclamation mark hairs are seen.

What is the diagnosis, and why is the distinction between scarring and nonscarring alopecia critical?

Frontal fibrosing alopecia (FFA)

Frontal fibrosing alopecia is a scarring (cicatricial) alopecia characterized by progressive recession of the frontal and temporal hairline. The pathognomonic trichoscopic finding is perifollicular scaling forming a collar around the follicular ostium, reflecting the perifollicular lymphocytic infiltrate that targets the follicular bulge region. Loss of follicular openings replaced by ivory-white fibrotic patches confirms permanent follicular destruction -- the hallmark of cicatricial alopecia. Lonely hairs (isolated terminal hairs surrounded by scarring) are another characteristic finding. The absence of black dots and exclamation mark hairs helps exclude alopecia areata. This distinction is critical because scarring alopecia causes irreversible hair loss, making early diagnosis and treatment essential to halt progression. Associated eyebrow loss is present in up to 80% of FFA patients.

Presence of yellow dots suggests:

• Alopecia areata (regular distribution, most common)
• Androgenetic alopecia (frontal predominance)
• Chronic telogen effluvium (sparse)
• Discoid lupus erythematosus (large yellow dots/follicular plugging)
• Dissecting cellulitis (3D soap bubble yellow dots)
• Congenital hypotrichoses, traction alopecia, kerion celsi (sparse)

Presence of black dots suggests:

• Active alopecia areata (disease activity marker)
• Tinea capitis
• Trichotillomania
• Dissecting cellulitis
• Chemotherapy-induced alopecia
• NOT androgenetic alopecia, NOT telogen effluvium, NOT normal scalp

Presence of exclamation mark hairs suggests:

• Active alopecia areata (specific)

Presence of comma/corkscrew hairs suggests:

• Tinea capitis (highly characteristic)

Presence of hair shaft thickness heterogeneity suggests:

• Androgenetic alopecia (hallmark)

Presence of white dots and loss of follicular ostia suggests:

• Scarring alopecia (any subtype)

Presence of flame hairs, V-sign, tulip hairs suggests:

• Trichotillomania (specific)

Algorithms assist in differential diagnosis. The most established algorithm differentiates female androgenetic alopecia from chronic telogen effluvium:

Major criteria (Rakowska et al.):

1. More than four yellow dots in four images (70-fold magnification) in the frontal area
2. Lower average hair thickness in the frontal area compared with the occiput
3. More than 10% of thin hairs (below 0.03 mm) in the frontal area

Minor criteria:

1. Increased frontal-to-occipital ratio of single-hair pilosebaceous units
2. Increased frontal-to-occipital ratio of vellus hairs
3. Increased frontal-to-occipital ratio of perifollicular discoloration

Diagnostic threshold: Two major criteria OR one major and two minor criteria -- 98% specificity for female androgenetic alopecia.

---

Check Your Understanding

How does dermoscopy differentiate alopecia areata from trichotillomania?

Alopecia areata shows yellow dots (empty follicles), black dots (broken hairs at the scalp surface), exclamation mark hairs (short tapered hairs), and short vellus hairs. Trichotillomania shows irregularly broken hairs at different lengths, black dots, coiled or hook-shaped hairs, tulip hairs (dark tulip-shaped tips), and flame hairs. The presence of exclamation mark hairs favors alopecia areata, while hair irregularity and flame hairs favor trichotillomania.

Key Takeaways

• Comma hairs (short, C-shaped, broken hairs) are characteristic of tinea capitis and should prompt KOH examination and fungal culture.
• Corkscrew hairs and zigzag hairs suggest trichotillomania or traction alopecia and are found in patches with irregular borders and varying hair lengths.
• Dystrophic hair shafts (irregular caliber, trichorrhexis nodosa, pili torti) visible under trichoscopy can guide diagnosis of genetic hair disorders without the need for hair pull testing.