Module 27: Differentiation -- Pattern Analysis and Melanoma-Specific Criteria; Rules and Algorithms

The clinical challenge in dermoscopy is not merely identifying individual structures but integrating them into a coherent diagnostic framework. Two complementary cognitive strategies are employed:

1. Heuristic (pattern recognition) -- Rapid, experience-driven evaluation based on matching the overall gestalt of a lesion to stored mental templates. Pattern analysis is the primary heuristic method. It requires significant experience to master but, once mastered, allows rapid and highly accurate evaluation.

2. Analytic (algorithmic) -- Structured, semi-quantitative scoring systems (ABCD rule, Menzies method, 7-point checklist, CASH) that guide the observer step-by-step through feature identification and scoring. These methods do not require significant experience and are best suited for novice dermoscopists.

As experience is gained, a natural shift occurs from predominantly analytic approaches to predominantly heuristic approaches. Importantly, studies show that both teaching methods improve diagnostic accuracy by approximately 20% in novices, but pattern analysis ultimately yields slightly better diagnostic accuracy and faster evaluation times than algorithmic methods.

In clinical practice, experienced dermoscopists use both approaches interactively -- pattern recognition for routine lesions and deliberate analytic reasoning when a case is complex, ill-defined, or unfamiliar.

Benign melanocytic lesions tend to manifest organized, symmetric patterns. Melanomas tend to manifest disorganized, asymmetric patterns with at least one melanoma-specific structure. However, there are important exceptions: some melanomas (amelanotic melanoma, nodular melanoma) can display organized/symmetric patterns, and some benign nevi (multicomponent pattern) can appear complex. Thus, the recognition of melanoma-specific structures is essential regardless of overall pattern assessment.

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4.1 The Pattern Analysis Approach

Pattern analysis for differentiating benign from suspect melanocytic lesions begins with a fundamental acknowledgment: the "critical element of becoming an expert is accruing the vast experience that enables experts to recognize patterns effortlessly, most of the time -- and to recognize, as well, when the signs and symptoms do not fit a pattern at all."

The recommended approach proceeds in two phases:

Phase 1 -- Build a mental library of benign patterns: Since benign lesions constitute the vast majority of lesions encountered in daily practice, the learner first builds extensive experience recognizing the 10 benign patterns of nevi (see Section 4.2 below). Nevi tend to exhibit symmetry of pattern, structure, and color -- they manifest an "organized pattern."

Phase 2 -- Identify deviations from benign patterns: Once familiarized with normal nevus patterns, suspicious lesions that deviate from those benign patterns are readily identified. Malignant lesions, including melanomas, usually deviate from benign patterns and display some degree of asymmetry of pattern, color, and structure -- they manifest a "disorganized pattern."

4.2 The 10 Benign Nevus Patterns

The following global patterns are characteristic of benign nevi. Any melanocytic neoplasm that deviates from these patterns should be viewed with caution.

#	Global Pattern	Definition	Clinical Association
1	Reticular diffuse	Diffuse homogeneous network with relatively uniform thickness and color of network lines; holes of relatively uniform size; network tends to fade at the periphery	Acquired nevi and small congenital nevi on the extremities
2	Reticular patchy	Homogeneous network in focal patches distributed in an organized manner, separated by homogeneous structureless areas lighter than the network lines; structureless areas are same color as background skin or slightly darker	Acquired nevi on the torso; superficial congenital nevi, especially lower extremity
3	Peripheral reticular with central hypopigmentation	Relatively uniform network at the periphery with a central homogeneous and hypopigmented structureless area (same color as background skin or slightly darker, but lighter than network lines)	Acquired nevi, more common in fair-skinned individuals
4	Peripheral reticular with central hyperpigmentation	Relatively uniform network at the periphery with a central homogeneous hyperpigmented structureless area or blotch (darker than network lines)	Acquired nevi, more common in darker-skinned individuals
5	Homogeneous tan, brown, or blue pigmentation (sometimes pink)	Primarily diffuse homogeneous structureless pattern; occasional globules and/or small focal network fragments may be evident	Tan = acquired nevi in fair skin; dark brown = congenital nevi; blue = blue nevi; pink = nevi in very fair-skinned/redheads (NB: amelanotic/hypomelanotic melanomas can appear similar but usually also reveal atypical vessels and/or shiny white structures)
6	Peripheral reticular with central globules	Relatively uniform network at the periphery with central globules	Often congenital nevi histopathologically
7	Peripheral globules with central network or homogeneous area and the starburst pattern	Central reticular or homogeneous component with peripheral globules; one row of uniform brown globules = Clark nevus in active radial growth; tiered (>1 row) globules = spitzoid morphology; classic starburst = streaks around entire perimeter	Clark nevi (growing), Spitz/Reed nevi in active radial growth
8	Globular (includes cobblestone)	Globules of similar shape, size, and color distributed symmetrically; globules usually round to oval; sometimes large and angulated (cobblestone appearance)	Congenital nevi (most commonly)
9	Two-component	Two different patterns present (reticular-globular, reticular-homogeneous, or globular-homogeneous); one half manifests one pattern, the other half manifests a different pattern	Benign nevi with dual pattern
10	Multicomponent	Definition 1 (benign): Organized and/or symmetrically distributed typical dots/globules, typical network, and homogeneous areas; axis of symmetry need only be in one axis. Definition 2 (caution): Symmetrically distributed globules, network, blotches, dots, veil, regression structures, and/or structureless areas with 3 or more structures required. A multicomponent pattern other than Definition 1 should be evaluated in context with the patient's other nevi (comparative approach). If it is the patient's signature pattern, it can be followed. If it is an outlier, biopsy should be considered.	Benign nevi (Definition 1); requires comparative approach (Definition 2)

4.3 Global Pattern Assessment

The first step in differentiating nevi from melanoma is evaluating the global pattern:

Step 1: Evaluate global pattern
 |
 +----+----+
 | |
 v v
ORGANIZED DISORGANIZED
(Symmetric) (Asymmetric)
 | |
 v v
Matches one Step 2: Evaluate for
of 10 benign melanoma-specific
nevus structures
patterns?
 | |
 Yes No
 | |
 v v
Likely Any melanoma-
benign specific structure
 present?
 |
 +----+----+
 | |
 Yes No
 | |
 v v
 Consider Feature-poor/
 melanoma featureless -->
 until consider digital
 proven monitoring
 otherwise

Critical exceptions to the organized = benign rule:

• Some melanomas display an organized pattern (e.g., amelanotic melanoma, nodular melanoma). Even in these cases, the recognition of at least one melanoma-specific structure or blue-black/gray color under dermoscopy will raise suspicion.
• Dermoscopic asymmetry by itself is NOT a prerequisite for the diagnosis of melanoma.
• A subset of flat, feature-poor or featureless/structureless melanomas may prove challenging to diagnose; however, dermoscopy provides useful information by identifying changes over time through digital monitoring.

Clinical Scenario

A 38-year-old woman presents with an 8 mm flat brown lesion on her left thigh. Dermoscopy shows a diffuse reticular pattern with relatively uniform network lines that fade at the periphery, with no atypical features, asymmetry, or additional structures. The pattern is organized and symmetric across both axes.

What benign pattern does this lesion display, and what would change your assessment?

Reticular Diffuse Pattern (Benign Nevus Pattern #1)

This is one of the 10 recognized benign nevus patterns: diffuse homogeneous network with uniform line thickness and color, holes of uniform size, fading at the periphery. It corresponds to a junctional or superficial compound acquired nevus. Features that would raise suspicion include: focal thickening or gray discoloration of network lines (atypical network), eccentric blotch, asymmetric streaks, blue-white veil, negative network, or any melanoma-specific structure. Any deviation from the organized pattern should prompt closer evaluation.

4.4 Melanoma-Specific Criteria Checklist

Any lesion that deviates from the benign patterns listed above and manifests at least one of the following melanoma-specific structures should be considered a melanoma until proven otherwise.

Dermoscopic Feature	Definition	Histopathologic Correlate
Atypical pigment network	Network with increased variability in color, thickness, and spacing of lines; asymmetrically distributed	Lines = pigmented keratinocytes or melanocytes along DEJ; holes = suprapapillary plate
Negative pigment network	Serpiginous interconnecting broadened hypopigmented lines surrounding elongated and curvilinear globules. Seen in de novo melanomas and melanomas arising in pre-existing nevi	Distorted/attenuated rete ridges with confluent nested melanocytes along DEJ (brown elongated globular structures) flanked by elongated/widened rete ridges (hypopigmented areas)
Angulated lines	Gray to brown lines meeting at acute angles creating a zig-zag pattern; can coalesce to form polygons (rhomboids); may appear as solid lines or lines composed of gray dots (pointillism). Mainly seen in melanoma on sun-damaged skin (lentigo maligna)	Flattening of DEJ, confluent melanocytes along DEJ, melanophages in papillary dermis
Irregular globules/clods	Clods, round or oval, with heterogeneity in size, shape, and/or color	Nests of nevomelanocytes at DEJ or dermis
Irregular dots	Dots, black or brown with heterogeneity in color and off-center distribution; often found with atypical network or toward the periphery of melanoma	Aggregates of melanocytes or melanin granules; if black = stratum corneum; if brown = epidermis below stratum corneum
Streaks (always at periphery): radial streaming, pseudopods	Radial streaming: radial and segmental lines. Pseudopods: radial and segmental lines with bulbous projections at tips	Confluent junctional nests of melanocytes at lesion periphery
Irregular blotch	Structureless zone with so much brown-black-blue pigment that it obscures other structures; classified as irregular if off-center or if multiple blotches present	Aggregates of melanin in stratum corneum or throughout all layers of epidermis with or without dermal involvement
Regression structures: peppering/granularity	Dots with gray color	Free melanin or melanophages in papillary dermis
Regression structures: scarlike depigmentation	White structureless zone lighter than surrounding normal skin; usually seen with peppering	Fibrotic papillary dermis
Shiny white structures (polarized dermoscopy only)	Shiny white lines oriented parallel and orthogonal to each other; may coalesce into grid of square-shaped white-lined structures. NOT to be confused with negative network (visible in both polarized and nonpolarized)	Altered matrix collagen and dermal fibroplasia
Blue-whitish veil	Structureless zone, blue with white "ground glass" haze found over a raised area; does NOT occupy the entire lesion	Heavily pigmented dermal melanocytes combined with compact orthokeratosis
Polymorphous vessels	Vessels with more than one morphology, usually consisting of dotted and linear serpentine vessels plus any other vessel morphology	Tumoral neo-angiogenesis in the dermis

4.5 Feature-by-Feature Comparison: Nevus vs. Melanoma

Feature	Nevus Version	Melanoma Version
Pigment network	Typical: uniform thickness, color, and spacing of lines; fades at periphery	Atypical: variable thickness, color, and spacing; asymmetric distribution
Negative network	Not typically present	Serpiginous hypopigmented lines surrounding elongated curvilinear globules
Dots	Regular: uniform in size and color, evenly distributed	Irregular: heterogeneous color, off-center distribution
Globules/clods	Regular: similar shape, size, and color; symmetrically distributed	Irregular: heterogeneous in size, shape, and/or color
Streaks	Circumferential (entire perimeter); seen in Spitz/Reed nevi in growth phase	Segmental (focal at periphery); asymmetric radial streaming or pseudopods
Blotch	Regular: central, symmetric (regular blotch)	Irregular: off-center or multiple blotches obscuring structures
Structureless areas	Homogeneous, symmetric; same color tone or slightly darker than background	Eccentric, asymmetric; variable colors; regression, blue-whitish veil
Vessels	Regular pattern: comma vessels (intradermal nevi)	Polymorphous: multiple vessel morphologies in a single lesion
Overall pattern	Organized, symmetric; one of 10 benign patterns	Disorganized, asymmetric; chaotic distribution of colors and structures

4.6 Important Diagnostic Nuances

1. Agreement on melanoma-specific structures is imperfect even among experts: Preliminary data suggest that agreement on the presence and spatial localization of melanoma-specific structures is poor even among experienced dermoscopists. Nevertheless, their presence increases the possibility of malignancy.

2. The heterogeneity principle: Irregular dots may be confused with irregular globules; however, the heterogeneity in size, shape, and color of the structure, and their chaotic distribution, will raise suspicion for melanoma irrespective of whether the observer classifies the structure as a dot or as a globule.

3. Both approaches are used interactively: Dermoscopic evaluation utilizes both heuristic and analytic approaches in an interactive fashion. Nonanalytic reasoning (pattern recognition) is essential to diagnostic expertise and is developed through practice and clinical experience. Deliberative analytic reasoning is the primary strategy when a case is complex, ill-defined, unusual, or when the physician has limited experience with the particular disease entity.

Check Your Understanding

How does the concept of 'dermoscopic symmetry' differ from clinical symmetry?

Dermoscopic symmetry evaluates the distribution and arrangement of colors and structures within the lesion, not just its overall shape. A lesion may appear clinically symmetric (round shape) but be dermoscopically asymmetric if the internal structures, colors, or patterns are unevenly distributed. Dermoscopic asymmetry is a more sensitive indicator of malignancy than clinical asymmetry.

Key Takeaways

• Specific dermoscopic features (e.g., arborizing vessels for BCC, comedo-like openings for SK) provide high positive predictive value for particular diagnoses.
• Sensitive features (e.g., any atypical pattern, any vessel irregularity) cast a wide net and are useful for screening but produce more false positives.
• The tension between sensitivity and specificity means that no single feature or algorithm is optimal for all clinical scenarios; the approach must be adapted to the pretest probability.

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Clinical Scenario

A 48-year-old man presents with a 10 mm pigmented lesion on his upper back. Dermoscopy reveals an atypical pigment network (broadened, irregular lines with gray coloration), an eccentric irregular blotch, regression structures (blue-gray peppering) in one quadrant, and shiny white lines under polarized light. Using the ABCD rule, you score: Asymmetry = 2, Border = 4, Color = 4, Dermoscopic structures = 4, yielding TDS = 7.45.

What does this TDS indicate, and which melanoma-specific structures are present?

Melanoma (TDS > 5.45)

A TDS above 5.45 indicates high suspicion for melanoma. This lesion manifests four melanoma-specific structures: (1) atypical pigment network, (2) irregular blotch, (3) regression structures, and (4) shiny white lines. The Menzies method would also be positive (no symmetry of pattern, no single color, plus at least one positive feature). The seven-point checklist scores at least 5 points (atypical network = 2, regression = 1, irregular blotch = 1, shiny white structures = 1). All four algorithms agree -- excisional biopsy is indicated.

4.7 Overview of Dermoscopic Algorithms

Several algorithms and scoring systems have been created to guide the observer in the dermoscopic decision-making process. This chapter covers four major systems:

• ABCD rule of dermoscopy
• Menzies method
• Seven-point checklist (classic and revised)
• CASH algorithm

All are relatively simple, accurate, and reproducible methods for dermoscopic evaluation. Although all have similar sensitivity, methods that rely on pattern analysis demonstrate superior specificity, making them the preferred methods utilized by experienced clinicians.

Important caveat: None of these algorithms has been updated since original publication. Many new melanoma-specific structures have been identified since (shiny white lines, negative network, angulated lines). These more newly identified structures should not be ignored by clinicians electing to use one of these algorithms.

4.8 ABCD Rule of Dermoscopy

The ABCD rule of dermoscopy is a semi-quantitative scoring system created by Stolz and colleagues in 1994 for the evaluation of pigmented lesions. It analyzes four criteria, each multiplied by a weighted factor. The four individual weighted scores are summed to produce the Final Dermoscopy Score (FDS), also called the Total Dermoscopy Score (TDS).

Criteria:

A -- Asymmetry (weighted factor: x1.3; range 0-2.6):

• Refers to the contour AND distribution of colors and structures within the lesion in none, one, or two perpendicular axes.
• Score 0 = no asymmetry (symmetric in both axes)
• Score 1 = mono-axial asymmetry (asymmetric in one axis)
• Score 2 = bi-axial asymmetry (asymmetric in both axes)
• Note: The ABCD rule and the CASH algorithm are the only methods that take into account both contour and content of the lesion during asymmetry evaluation.

B -- Border sharpness (weighted factor: x0.1; range 0-0.8):

• Refers to the abrupt cutoff of pigmentation at the perimeter.
• Evaluated by tracing four imaginary lines that divide the lesion into eight pie-shaped sections.
• A score of 1 is given to each segment presenting with an abrupt cutoff of pigment.
• Score range: 0-8

C -- Colors (weighted factor: x0.5; range 0.5-3.0):

• The lesion is evaluated for the presence of each of six colors:

1. White
2. Red
3. Light brown
4. Dark brown
5. Blue-gray
6. Black

• A score of 1 is given to each color present.
• Score range: 1-6

D -- Dermoscopic structures (weighted factor: x0.5; range 0.5-2.5):

• The lesion is evaluated for the presence of five structures:

1. Pigment network
2. Branched streaks
3. Dots
4. Globules (aggregated globules)
5. Homogeneous/structureless areas (including hyperpigmented blotches, hypopigmented areas, depigmented or scarlike areas involving >10% of surface area)

• A score of 1 is given to each structure present.
• Score range: 1-5

Calculation:

TDS = (Asymmetry score x 1.3) + (Border score x 0.1) + (Color score x 0.5) + (Structure score x 0.5)

Interpretation thresholds:

TDS Range	Interpretation
< 4.75	Benign
4.75 - 5.45	Suspicious -- close follow-up or biopsy recommended
> 5.45	Highly suggestive of malignancy -- biopsy/excision indicated

Total possible range: 1.0 to 8.9

Performance: Sensitivity 78-98%; Specificity 45-90% (varies with examiner experience).

4.9 Menzies Method

The Menzies method was developed to differentiate invasive melanomas from other pigmented lesions. It evaluates 11 dermoscopic criteria classified into negative features (2) and positive features (9).

Decision rule: For the diagnosis of melanoma, BOTH negative features must be ABSENT and at least ONE positive feature must be PRESENT.

Negative Features (neither can be present in melanoma):

#	Negative Feature	Description
1	Symmetrical pigmentation pattern	Symmetric pigment pattern across all axes
2	Presence of only one color	Only one of the following colors: tan, dark brown, black, gray, blue, or red

The two negative features have demonstrated a low sensitivity for melanoma (i.e., most melanomas will lack these features, making them good at ruling melanoma in when absent). Their presence essentially excludes the diagnosis of melanoma.

Positive Features (at least one must be present to consider melanoma):

#	Positive Feature	Description
1	Multiple colors	Presence of five or more colors (from: tan, dark brown, black, gray, blue, red)
2	Blue-white veil	Irregular and confluent blue pigmentation with an overlying white "ground glass" film, not associated with red-blue lacunae
3	Multiple brown dots	Aggregations of dark brown dots, usually within the body of the lesion
4	Multiple blue/gray dots	Diffuse, partly aggregated dots, "pepper-like" in appearance
5	Peripheral black dots or globules	Black dots or globules at or near the edge of the lesion
6	Broadened network	Pigment network with areas of thick grids
7	Pseudopods	Finger-like projections with small knobs at their tips, directly connected to the tumor body or the pigment network
8	Radial streaming	Radial and asymmetric linear extensions at the edge of the lesion
9	Scarlike depigmentation	White, irregular area of depigmentation

The nine positive features have a high specificity for melanoma (>85%).

Application logic:

Step 1: Are BOTH negative features present?
 |
 +----+----+
 | |
 Yes No (at least one negative feature is absent)
 | |
 v v
Melanoma Step 2: Is at least ONE positive feature present?
EXCLUDED |
 +----+----+
 | |
 Yes No
 | |
 v v
 Suspect Melanoma
 MELANOMA less likely

Performance: Sensitivity 85-92% (for pigmented melanoma 86-95%; for amelanotic melanoma 54%); Specificity 38-78%; Diagnostic accuracy 83%.

4.10 The Seven-Point Checklist

The seven-point checklist evaluates seven dermoscopic features frequently associated with melanoma, categorized into major and minor criteria with differential weighting.

Classic Seven-Point Checklist:

Major Criteria (2 points each):

Criterion	Definition	Classic Score	Revised Score
Atypical pigment network	Prominent (hyperpigmented or thick) and irregular network	2	1
Blue-whitish veil (white-blue areas)	Irregular, structureless white-blue area with an overlying "ground glass" film; cannot occupy the entire lesion	2	1
Atypical vascular pattern	Linear irregular or dotted vessels, irregularly distributed outside areas of regression	2	1

Minor Criteria (1 point each):

Criterion	Definition	Classic Score	Revised Score
Radial streaming (streaks)	Radial and asymmetric linear or bulbous projections at the edge of the lesion	1	1
Irregular blotches	Black, brown, and/or gray structureless areas with irregular shape or distribution	1	1
Irregular dots and globules	Black or brown round structures irregularly distributed	1	1
Regression structures	White scarlike depigmentation and/or "peppering"	1	1

Scoring:

• Major criteria score range: 0-6 (3 criteria x 2 points each)
• Minor criteria score range: 0-4 (4 criteria x 1 point each)
• Total score range: 0-10

Classic threshold: Total score of 3 or more = suggestive of melanoma.

Revised Seven-Point Checklist:

The revised version proposes that the presence of ANY criterion (major or minor) is sufficient to consider a lesion suspicious for melanoma. The threshold for biopsy is lowered to a total score of 1 (instead of 3). Each criterion receives a score of 1 (no differential weighting). This achieves higher sensitivity at the cost of lower specificity.

The authors acknowledge that a sensitive and specific method to diagnose melanoma requires that additional factors and context be taken into account during examination, including:

• Clinical characteristics of the lesion
• Age and skin type of patient
• Location of lesion
• Whether the lesion is an outlier lesion (comparative approach)
• Whether the lesion has changed during follow-up

Performance (Classic): Sensitivity 62-95% (amelanotic melanoma 41%); Specificity 35-97%. Performance (Revised): Sensitivity 88%; Specificity 75%.

Key Takeaways

• Pattern-based differentiation uses global assessment (overall architecture) followed by local feature analysis (specific structures) to reach a diagnosis.
• Criteria-based rules (checklists, scoring systems) standardize the diagnostic process and are particularly valuable for less experienced dermoscopists.
• Expert dermoscopists integrate pattern recognition, probabilistic reasoning, and clinical context simultaneously, achieving diagnostic accuracy that exceeds any single algorithm.

4.11 CASH Algorithm

The CASH (Color, Architecture, Symmetry, and Homogeneity) algorithm was developed by Henning and colleagues in 2007 as a comprehensive scoring system. Total score range is 2-17.

C -- Color (score range 1-6): The lesion is evaluated for the presence of each of six colors. One point is given for each color present:

Color	Score
Light brown	1
Dark brown	1
Brown	1
Red	1
White	1
Blue	1

A -- Architectural disorder (score range 0-2): Refers to order versus disorder in the distribution of dermoscopic structures:

Degree	Description	Score
None/mild	Colors and dermoscopic structures distributed in an organized or slightly disordered manner	0
Moderate	Dermoscopic structures lose their uniformity and are distributed in an irregular manner	1
Marked	Arrangement of colors and dermoscopic structures is completely disorganized (chaotic)	2

S -- Symmetry (score range 0-2): Takes into account shape AND dermoscopic structures:

Symmetry	Score
Bi-axial symmetry	0
Mono-axial symmetry	1
Bi-axial asymmetry	2

H -- Homogeneity/Heterogeneity of dermoscopic structures (score range 1-7): The lesion is evaluated for the number of distinct dermoscopic structures present. One point per structure:

Structure	Score
Network	1
Dots/globules	1
Streaks/pseudopods	1
Blue-white veil	1
Regression structures	1
Blotches	1
Polymorphous vessels	1

Calculation:

CASH score = Color score + Architectural disorder score + Symmetry score + Homogeneity score

Interpretation threshold:

CASH Score	Interpretation
< 8	Likely benign
>= 8	Suspicious for melanoma

Performance: Sensitivity 87-98%; Specificity 67-68%.

4.12 Comparative Analysis of Algorithms

All four algorithms share common principles:

• They assess for asymmetry/symmetry in some form
• They evaluate the number and diversity of colors
• They identify the presence of specific dermoscopic structures
• They produce a numeric score compared against a threshold

Key differences:

Feature	ABCD Rule	Menzies	7-Point Checklist	CASH
Scoring type	Weighted semi-quantitative	Binary (negative/positive)	Weighted (classic) or unweighted (revised)	Unweighted additive
Number of criteria	4 composite criteria	11 (2 negative + 9 positive)	7 (3 major + 4 minor)	4 composite criteria
Asymmetry assessment	Contour + content	Pattern only	Not directly scored	Shape + structures
Border evaluation	Yes (8 segments)	No	No	No
Color scoring	6 colors, weighted	Binary (1 vs. 5+ colors)	Not directly scored	6 colors, unweighted
Threshold	4.75 (suspicious), 5.45 (malignant)	Binary rule	3 (classic), 1 (revised)	8
Best for	General screening	Invasive melanoma vs. pigmented lesions	Structured teaching, sequential monitoring	Comprehensive scoring
Original publication	Stolz et al. 1994	Menzies et al. 1996	Argenziano et al. 1998	Henning et al. 2007

4.13 When to Use Which Algorithm

For novice dermoscopists:

• Start with the seven-point checklist -- it focuses on a limited number of well-defined structures and provides a clear scoring system for learning.
• The ABCD rule provides a systematic framework that reinforces attention to asymmetry, border, color, and structures.
• The Menzies method is useful for its binary decision logic -- first check for the two exclusion criteria, then look for positive features.

For experienced clinicians:

• Pattern analysis is the preferred method as it demonstrates superior specificity and faster evaluation times.
• Algorithms serve as a structured backup when encountering complex or unfamiliar lesions.

For screening in primary care/non-specialist settings:

• The revised seven-point checklist (threshold of 1) maximizes sensitivity, which is appropriate when the primary goal is not to miss melanoma, accepting a higher false-positive rate.
• The CASH algorithm provides a comprehensive assessment that is relatively straightforward to apply.

For research and education:

• Any algorithm can be used as a standardized framework for teaching and comparison.
• The ABCD rule is widely studied and has extensive validation data across different populations.

4.14 Algorithm Limitations and Pitfalls

1. No algorithm has been updated since its original publication -- newly identified melanoma-specific structures (shiny white lines, negative network, angulated lines) are not incorporated into any scoring system.

2. All algorithms require pre-classification as melanocytic: For all analytically based scoring algorithms, a given pigmented lesion must first be classified as melanocytic (nevus vs. melanoma) rather than non-melanocytic. Only after ruling out a non-melanocytic diagnosis can the algorithms be applied.

3. Amelanotic melanoma is poorly detected: All algorithms have significantly lower sensitivity for amelanotic and hypomelanotic melanomas compared to pigmented melanomas.

4. Nodular melanoma challenges: Many classic dermoscopic criteria are based on features observed in superficial spreading melanoma with melanin/melanocytes in the epidermis or at the DEJ. Nodular melanomas may lack these criteria.

5. Context matters: None of the algorithms incorporate patient age, skin type, lesion location, personal/family history, or change over time -- all of which are important contextual factors for clinical decision-making.

6. Sensitivity vs. specificity tradeoff: Lowering the scoring threshold (e.g., revised 7-point checklist) increases sensitivity but decreases specificity, leading to more unnecessary biopsies.

7. Inter-observer variability: Agreement on the presence of specific dermoscopic structures is imperfect even among experts, which affects the reproducibility of all scoring systems.

Check Your Understanding

What are the 'specific patterns' that allow confident benign diagnosis without further algorithmic analysis?

Specific benign patterns include: the comma vessel pattern (dermal nevus), the strawberry pattern (actinic keratosis), the lacunar pattern (hemangioma), the starburst pattern in a young patient (Spitz/Reed nevus), the parallel furrow pattern (acral nevus), the cerebriform/fissure pattern (seborrheic keratosis), and the central white patch with peripheral network (dermatofibroma). These patterns have high positive predictive values for their respective diagnoses.

Key Takeaways

• Combining specific features (high PPV) with sensitive screening criteria (high NPV) in a sequential approach optimizes both melanoma detection and biopsy efficiency.
• The number needed to biopsy (NNB) is a clinically meaningful metric: expert dermoscopists achieve NNB of 3-5 for melanoma, while naked-eye examination has NNB of 15-30.
• Continuous learning and feedback (correlating dermoscopic impressions with histologic outcomes) is the most effective way to improve individual diagnostic performance.

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Criterion	Score Options	Raw Score Range	Weighted Factor	Final Score Range
A -- Asymmetry	0 = no asymmetry; 1 = mono-axial; 2 = bi-axial	0-2	x 1.3	0 - 2.6
B -- Border	0-8 segments with sharp cutoff	0-8	x 0.1	0 - 0.8
C -- Colors	1 point per color (white, red, light brown, dark brown, blue-gray, black)	1-6	x 0.5	0.5 - 3.0
D -- Structures	1 point per structure (network, branched streaks, dots, globules, structureless areas)	1-5	x 0.5	0.5 - 2.5
Total Dermoscopy Score				1.0 - 8.9

Thresholds: < 4.75 = benign | 4.75-5.45 = suspicious | > 5.45 = malignant

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Category	Feature	Description	Rule
Negative Feature 1	Symmetrical pattern	Symmetric pigment pattern across all axes	BOTH negative features must be ABSENT to consider melanoma
Negative Feature 2	Only one color	Only 1 of 6 colors (tan, dark brown, black, gray, blue, red)
Positive Feature 1	Multiple colors	5 or more colors present	At least ONE positive feature must be PRESENT to consider melanoma
Positive Feature 2	Blue-white veil	Irregular confluent blue pigmentation + white "ground glass" film
Positive Feature 3	Multiple brown dots	Aggregations of dark brown dots within lesion body
Positive Feature 4	Multiple blue/gray dots	Diffuse, "pepper-like" partly aggregated dots
Positive Feature 5	Peripheral black dots/globules	Black dots or globules at/near lesion edge
Positive Feature 6	Broadened network	Pigment network with areas of thick grids
Positive Feature 7	Pseudopods	Finger-like projections with knobs at tips, connected to tumor body
Positive Feature 8	Radial streaming	Radial, asymmetric linear extensions at lesion edge
Positive Feature 9	Scarlike depigmentation	White, irregular area of depigmentation

Decision: Melanoma = BOTH negative features ABSENT + at least 1 positive feature PRESENT.

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Category	Criterion	Definition	Classic Score	Revised Score
Major	Atypical pigment network	Prominent, hyperpigmented/thick, irregular network	2	1
Major	Blue-whitish veil	Irregular structureless white-blue area with "ground glass" film; not occupying entire lesion	2	1
Major	Atypical vascular pattern	Linear irregular or dotted vessels, irregularly distributed outside regression areas	2	1
Minor	Radial streaming (streaks)	Radial, asymmetric linear or bulbous projections at lesion edge	1	1
Minor	Irregular blotches	Black, brown, and/or gray structureless areas with irregular shape/distribution	1	1
Minor	Irregular dots and globules	Black or brown round structures irregularly distributed	1	1
Minor	Regression structures	White scarlike depigmentation and/or "peppering"	1	1
	Maximum possible score		10	7

Classic threshold: Total >= 3 = suspicious for melanoma Revised threshold: Total >= 1 = suspicious for melanoma (any single criterion)

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Criterion	Sub-items	Score	Score Range
Color	Light brown (1), Dark brown (1), Brown (1), Red (1), White (1), Blue (1)	1 per color present	1-6
Architectural disorder	None/mild (0), Moderate (1), Marked (2)	0, 1, or 2	0-2
Symmetry	Bi-axial symmetry (0), Mono-axial (1), Bi-axial asymmetry (2)	0, 1, or 2	0-2
Homogeneity	Network (1), Dots/globules (1), Streaks/pseudopods (1), Blue-white veil (1), Regression structures (1), Blotches (1), Polymorphous vessels (1)	1 per structure present	1-7
Total CASH Score			2-17

Threshold: Total >= 8 = suspicious for melanoma

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