Skin CancerAdvanced · 7 min read

Acral Lentiginous Melanoma

Parallel ridge pattern is the dermoscopic hallmark, but up to half of acral melanomas lack it; the BRAAFF checklist combines six features to deliver 93% sensitivity and 87% specificity.

By Dr. Yehonatan KaplanPublished Updated

In brief

Acral lentiginous melanoma (ALM) is the most common melanoma subtype in non-white populations (over 70% of melanomas in African Americans, around 50% in Asian patients) but represents under 10% of melanomas in white populations. Absolute incidence is similar across ethnicities; the proportion difference reflects nonacral melanoma rates in lighter skin. ALM has worse prognosis attributed mainly to delayed diagnosis. Dermoscopy of acral skin requires a site-specific framework because the dermoglyphic ridges and furrows produce parallel-line patterns rather than network. The parallel ridge pattern (PRP) is the classical melanoma sign, but its absence does not exclude diagnosis: up to 50% of ALMs lack PRP, requiring the BRAAFF holistic algorithm.

Clinical content

01Acral skin anatomy drives the dermoscopic vocabulary. The epidermis is flattened with prominent ridges (cristae superficiales, wider) and furrows (sulci superficiales, thinner), and sweat-gland orifices open exclusively on the ridges. Melanocytic proliferations follow these structures, producing parallel-line patterns. In benign nevi, melanocytic nests sit around the crista profunda limitans (under the surface furrows), so pigment appears in furrows: parallel furrow pattern (PFP). In melanoma, atypical melanocytes proliferate around the crista profunda intermedia (under the surface ridges), so pigment appears on ridges: parallel ridge pattern (PRP). Sweat-gland orifices are the anatomic landmark distinguishing ridges (wider) from furrows (thinner) when pigmentation is intense.

02Parallel ridge pattern (PRP) carries 99% specificity for ALM in published series and represents the strongest single dermoscopic predictor (16-fold odds in Lallas's BRAAFF analysis). When pigment intensity makes ridge-versus-furrow assignment unclear, focus on the lesion periphery where lines may be less confluent, and look for sweat-gland orifices on the pigmented stripe. PRP can also occur in subcorneal hemorrhage (sharp borders, satellite blood spots distinguish it) and rarely in drug-induced or exogenous pigmentation, but in any other context PRP mandates excision.

03Parallel furrow pattern (PFP) is the most common benign acral pattern, appearing in 60% of acral nevi. PFP shows pigment along furrows (the thinner lines), often as single or double lines. Variants include the lattice-like pattern (pigment along furrows plus crossing lines, common on arches) and the double-line pattern (two parallel pigmented lines along each furrow). All PFP variants are negative predictors for ALM (one point off in BRAAFF).

04Fibrillar pattern shows fine pigmented filaments oriented perpendicular to ridges and furrows, classically at pressure-loaded sites (heel, forefoot, ball of the foot). The pattern represents melanin in obliquely sectioned stratum corneum from chronic mechanical pressure. Fibrillar is benign and is the second negative predictor in BRAAFF (one point off). Importantly, even ALM can occasionally show focal fibrillar areas, so symmetric fibrillar pattern is benign but asymmetric or partial fibrillar in an otherwise atypical lesion does not rule out melanoma.

05Lattice-like pattern crosses furrows symmetrically and is common on the arch of the foot. It is not specifically protective in BRAAFF (does not score) but is a recognized benign acral variant. Confusion arises when lattice extends onto ridges; the diagnostic decision then rests on overall symmetry.

06BRAAFF checklist (Lallas 2015) distills six variables into a clinically applicable scoring system: B (irregular Blotch, +1), R (parallel Ridge pattern, +3), A (Asymmetry of structures, +1), A (Asymmetry of colors, +1), F (parallel Furrow pattern, -1), F (Fibrillar pattern, -1). A total score of 1 or higher triggers excision. The algorithm achieves 93% sensitivity and 87% specificity, validated across in-situ and invasive ALMs and against both excised and non-excised acral nevi.

07Multicomponent acral pattern (defined as three or more dermoscopic structures coexisting asymmetrically) characterized 51% of invasive ALMs in Lallas's series. Structureless pattern characterized 38% of invasive ALMs. Together, multicomponent and structureless dominate the global appearance of advanced ALM, while in-situ ALM still tends to show parallel-line patterns (62%) with subtle asymmetry. The shift from parallel-line to multicomponent global pattern roughly tracks invasion depth.

08Saida's three-step algorithm (revised 2011) provides a complementary triage approach. Step 1: Is there a parallel-pattern? If yes, proceed to Step 2; if no, the lesion is likely non-melanocytic. Step 2: Is the parallel pattern PRP? If yes, excise. Step 3: If PFP/lattice/fibrillar, evaluate for asymmetry, irregular pigmentation, irregular dots/globules, or blue-white veil. Saida's approach is conceptually compatible with BRAAFF, with BRAAFF providing the explicit scoring and validation in a Western and Asian combined population.

09Subungual melanoma is anatomically related but biologically distinct. The pigmented nail band must be evaluated for color (gray colors favor non-melanoma; brown with dots and globules favors melanocytic), homogeneity of the pigmented lines, band width, and Hutchinson sign (extension to the proximal/lateral nail fold). Mucosal melanoma similarly requires pattern analysis distinct from acral skin: structureless pattern dominates, and gray, blue, or white colors raise melanoma suspicion.

Key dermoscopic features

Parallel ridge pattern (PRP)
Hallmark of acral melanoma; 16-fold OR in BRAAFF multivariate analysisPigment along the wider ridges, with sweat-gland orifices on the pigmented stripe
Parallel furrow pattern (PFP)
Most common benign acral nevus pattern (60% of nevi); BRAAFF -1Pigment along the thinner furrows, single or double lines, sweat-gland orifices on adjacent unpigmented ridges
Fibrillar pattern
Benign nevus on pressure-loaded sites (heel, forefoot); BRAAFF -1Fine pigmented filaments oriented perpendicular to ridges and furrows
Lattice-like pattern
Benign acral nevus variant on archesPigment along furrows with regular crossing lines
Irregular blotch
Heterogeneous pigment concentration; 4-fold OR for ALM; BRAAFF +1Dark brown to black structureless area, eccentric or asymmetric within the lesion
Asymmetry of structures
Architectural disorder; BRAAFF +1Identifiable structures unequally distributed across the lesion axes
Asymmetry of colors
Color heterogeneity; BRAAFF +1; 7-fold OR for ALMIdentifiable colors unequally distributed across the lesion axes
Multicomponent global pattern
Three or more dermoscopic structures present asymmetrically; characterizes 51% of invasive ALMCombination of parallel-line, structureless, blotch, and other features without symmetric organization
Structureless pattern (acral)
Common in advanced invasive ALM (38%)Diffuse coloration without identifiable parallel-line, network, or globular structure
Blue-white veil (acral)
Dermal invasion in invasive ALM (33%)Confluent blue blotch with overlying whitish ground-glass haze
Atypical vessels and milky-red areas
Vertical-growth phase; rare in early ALMPolymorphic linear-irregular vessels, sometimes with structureless pink zones

High yield clinical points15 pearls in 4 groups

Recognition & pattern analysis

8 points
1
Sweat glands locate the ridges. When pigmentation is intense and ridges and furrows are hard to distinguish, look for sweat-gland orifices: they open on ridges. Pigment with sweat glands on the stripe = PRP; pigment with sweat glands on the unpigmented adjacent stripe = PFP.
2
Asymmetry overrides benign patterns. Even a lesion with PFP or fibrillar pattern should be excised if it shows marked asymmetry of colors plus structures, or if it shows irregular blotches. The BRAAFF arithmetic guarantees this.
9.5%
Age matters on acral skin. Acral melanoma is rare under 20 years; the youngest BRAAFF patient was 21. Mean ALM age is 67 versus 36 for nevi, with each year of age adding 9.5% melanoma risk in adjusted models. Childhood acral lesions almost always represent nevi.
51%
Multicomponent + structureless = advanced ALM. Invasive ALM most commonly shows multicomponent (51%) or structureless (38%) global patterns. When parallel lines are absent, evaluate for these patterns plus blotches and asymmetry.
5
Fibrillar can occur focally in ALM. Even though fibrillar is a negative BRAAFF predictor, a focal fibrillar area in a lesion that also shows asymmetry, blotches, or PRP elsewhere does not exclude melanoma. Evaluate the entire lesion.
6
Subungual melanoma has its own rules. Brown with dots/globules along the band favors melanocytic origin; gray favors lentigo, drug-induced pigment, or ethnic discoloration. Variable line color, thickness, and spacing within a wide band plus Hutchinson sign favor melanoma over nevus.
7
Mucosal melanoma color rule is inverted. On mucosa, brown predominates in benign tumors; gray, blue, or white shifts suspicion toward melanoma. Structureless pattern dominates mucosal melanoma, while benign mucosal pigmentation typically shows globules, lines, or circles.
8
Delayed diagnosis drives prognosis. ALM mortality reflects late presentation more than intrinsic biology. Routine examination of palms, soles, and nails (which patients often hide and clinicians often skip) is the single most cost-effective ALM screening intervention.

Diagnostic criteria & thresholds

2 points
89%
Acral nevi favor soles over palms. Around 89% of acral lesions in the BRAAFF series were plantar; only 11% palmar. Site-frequency reflects normal nevus distribution and does not change diagnostic criteria.
2
Saida's three-step algorithm complements BRAAFF. Step 1 looks for parallel-pattern; step 2 distinguishes PRP from PFP/fibrillar; step 3 evaluates additional melanoma criteria. Conceptually equivalent to BRAAFF but framed as a triage decision tree.

Pitfalls & mimics

2 points
38%
Roughly two-thirds of ALMs lack PRP. Lallas's series showed PRP in only ~38% of ALMs (50% of in situ, 33% of invasive). Reliance on PRP alone misses most acral melanomas, hence the need for the BRAAFF algorithm.
2
Subcorneal hemorrhage mimics PRP. Acral subungual or subcorneal blood can produce a pseudo-ridge pattern. Sharp borders, satellite spots, peripheral push-out as the stratum corneum sheds, and absence of melanin under polarization distinguish hemorrhage from PRP.

When to biopsy

3 points
99%
PRP wins outright. Parallel ridge pattern, when unambiguous, mandates excision regardless of any other finding. It carries 99% specificity for ALM and was the strongest predictor in BRAAFF (16-fold odds).
93%
BRAAFF: a six-variable checklist. Blotch +1, Ridge +3, Asymmetry of structures +1, Asymmetry of colors +1, Furrow -1, Fibrillar -1. Score ≥1 triggers excision. Sensitivity 93%, specificity 87%, AUC 0.95.
or 0
Symmetric PFP or fibrillar = benign. A lesion showing only parallel furrow pattern or only fibrillar pattern, without asymmetry or blotches, is very likely benign and does not need excision (BRAAFF score -1 or 0).

Lectures covering this topic11 lectures

AAD 2026F095 · #01
Onychoscopy
Onychoscopy Faculty (AAD 2026)
AAD 2026F095 · #02
Volar Dermoscopy: Palmar and Plantar Skin Melanocytic
Nadeem Marghoob, DO
AAD 2026U004 · #03
Dermoscopy to the Rescue: Melanoma
Kelly C. Nelson, MD, FAAD
AAD 2026U041 · #01
Dermoscopy Quiz
David L. Swanson, MD
Excellence (main)DE-MAIN · #06
Acral and Nail Lesions
G. Argenziano and A. Lallas
Excellence Intl 2025DE-INTL · #04
Acral Update
Giuseppe Argenziano
Excellence Intl 2025DE-INTL · #12
Does Size Matter
Aimilios Lallas
Excellence PediatricDE-PED · #02
Miscellaneous Pediatric Lesions
Vincenzo Piccolo and Giuseppe Argenziano
Academy 2025ACAD25 · #10
Volar Lesions
Ashfaq A. Marghoob
ADM 2025ANNUAL13 · #04
Approach to Evaluating Volar Lesions
Richard Usatine, MD
ADM 2025ANNUAL13 · #15
Dermoscopy of Non-White Skin
Richard Usatine, MD

Notable updates & conceptual milestones6 updates

Parallel ridge versus parallel furrow pattern

2004

Saida 2004 multicenter Japanese study established the discriminatory power of pigment distribution along ridges versus furrows, founding modern acral dermoscopy.

Saida three-step algorithm

2011

Revised 2011 triage algorithm distinguishing parallel-pattern from non-parallel-pattern, then PRP from PFP/fibrillar, then evaluating additional melanoma criteria.

BRAAFF checklist

2015

Lallas 2015 multicenter analysis of 603 lesions yielding the six-variable scoring scheme with 93% sensitivity, 87% specificity, validated across in-situ and invasive ALMs and across populations.

International Dermoscopy Society multicenter study on acral melanoma

2013

Braun 2013 collaborative analysis demonstrated that acral nevus criteria (PFP, fibrillar) can occur focally in ALM, supporting holistic rather than single-criterion evaluation.

Recognition of advanced ALM as multicomponent or structureless

2015

Empirical demonstration that parallel-line patterns characterize early in-situ ALM, while invasive tumors more often show multicomponent or structureless global patterns, paralleling SSM evolution.

Pediatric and young-adult nail matrix melanoma vigilance

2025

Case-series evidence that nail matrix melanoma occurs under age 40 with most lesions in situ at diagnosis. Spiral melanonychia (long considered benign) appeared in a quarter of melanoma cases, supporting re-biopsy when serial dermoscopy shows progression.

Bottom line

Parallel ridge pattern is the dermoscopic hallmark, but up to half of acral melanomas lack it; the BRAAFF checklist combines six features to deliver 93% sensitivity and 87% specificity.

15 clinical points · 6 recent updates · 12 references

References

Sources cited in the lecture content or that underpin the clinical points above. Verify with primary sources before practice changes.

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