Acral lentiginous melanoma dermoscopy

What is acral lentiginous melanoma?

Acral lentiginous melanoma is a type of melanoma arising on the palms of the hands, soles of the feet, or the underside of fingers or toes.

What are the clinical features of acral lentiginous melanoma?

Acral lentiginous melanoma starts as a slowly enlarging flat patch of discoloured skin.

The characteristics of acral lentiginous melanoma include:

• Large size: > 6 mm and often several centimetres or more in diameter at diagnosis
• Variable pigmentation: most often a mixture of brown, and blue-grey, black and red colours
• A smooth surface at first, later becoming thicker with an irregular surface that may be dry or wart-like
• Ulceration or bleeding.

Acral lentiginous melanoma 

 

Acral lentiginous melanoma 

What are the dermoscopic features of acral lentiginous melanoma?

The most frequently observed dermoscopic features of acral lentiginous melanoma are:

1. Parallel ridge pattern (furrows remain relatively hypopigmented)
2. Asymmetrical structure and colours
3. Multicomponent pattern: a combination of many pigmentation patterns
4. Diffuse pigmentation of different shades of brown colour not respecting furrows or ridges.

Parallel ridge pattern, asymmetrical structure and diffuse pigmentation 

Asymmetrical structure and colour 

Parallel ridge pattern, asymmetrical structure and diffuse pigmentation 

Asymmetrical structure and colour with multicomponent pattern 

Asymmetrical structure and colour with multicomponent pattern 

Parallel ridge pattern with diffuse pigmentation 

The use of the BRAAFF algorithm in the dermoscopic diagnosis of acral lentiginous melanoma

In this algorithm, one point is required to make the diagnosis of melanoma [1].

• B: blotch, irregular +1
• R: ridge pattern, parallel +3
• A: asymmetry of structures +1
• A: asymmetry of colours +1
• F: furrow pattern, parallel -1
• F: fibrillar pattern -1

Using the BRAAF algorithm to diagnose acral melanoma

Irregular blotch, ridge pattern, asymmetry of structures and colours BRAAF 6 

Irregular blotch, ridge pattern, asymmetry of structures and colours BRAAF 6 

Ridge pattern, asymmetry of structures and colours BRAAF 5 

Using the BRAAF algorithm to diagnose acral naevus

Parallel furrow pattern BRAAF -1 

Fibrillar pattern BRAAF -1 

Parallel furrow, fibrillar pattern BRAAF -2 

What is the dermoscopic differential diagnosis of acral lentiginous melanoma?

It can be clinically and dermoscopically challenging to make the correct diagnosis in pigmented acral lesions. The following are differential diagnoses of acral lentiginous melanoma.

Acral naevus

• Pigmentation on the ridges of the surface skin markings is characteristic of early acral melanoma.
• Pigmentation along the furrows of the skin markings is characteristic of acral naevus.

These dermoscopic patterns are termed the parallel ridge pattern and the parallel furrow pattern, respectively. The sensitivity and specificity of the parallel ridge pattern in diagnosing early acral melanoma is 86% and 99%, respectively. However, dermoscopic features in acral naevus (especially congenital acral naevus) sometimes mimic the parallel ridge pattern [2].

Haemorrhage

The presence of a red-black homogeneous pigmentation, often combined with satellite globules is most likely indicative of haemorrhage. A positive scratch test (where removing a sample of the surface of the skin surface reveals blood) may be considered as an additional diagnostic clue to differentiate from melanoma [3].

Viral wart

Irregular pigmentation at the edge of a warty nodule could be indicative of melanoma [4].

Tinea nigra

Tinea nigra, a superficial fungal infection caused by Phaeoannellomyces werneckii, presents as a hyperpigmented, nonscaling macule of variable size and shape. Typically lacking induration, erythema, or pruritus, these 'ink spot' lesions may resemble junctional naevus or melanoma [5].

Dermoscopy of acral naevus showing parallel ridge pattern 

Dermoscopy of subcorneal haemorrhage showing red/brown structureless parallel ridge pattern 

Viral wart 

Tinea nigra 

What is the histological explanation of acral lentiginous melanoma?

The pathological diagnosis of melanoma can be very difficult. Histological features of acral lentiginous melanoma include an asymmetrical proliferation of melanocytes at the dermo-epidermal junction.

Preferential proliferation patterns of early melanoma cells and naevus cells in acral volar skin. Early melanoma cells (red dots in the diagram below) are mainly found as individual cells in the crista profunda intermedia under the surface ridge. In contrast, nests of acral naevus cells (blue dots in the diagram) are seen in the crista profunda limitans under the surface furrow [6].

Diagram of acral volar skin