Differentials
Benign/dysplastic melanocytic naevi
SIGNS / SYMPTOMS
Benign naevi or naevi that are moderately or severely dysplastic may be similar in appearance to melanoma.
Benign lesions tend to have a more uniform appearance in shape and colour when examined with the naked eye and usually lack worrying dermoscopic features, such as a blue/white veil, and are less likely than melanoma to itch or bleed.
INVESTIGATIONS
Clinical examination by a dermatologist.
The diagnostic test is skin biopsy.
Seborrhoeic keratosis
SIGNS / SYMPTOMS
Seborrhoeic keratoses demonstrate a waxy, 'stuck on', often hyperkeratotic appearance.
On dermoscopic evaluation, presence of horned cysts and hairpin-shaped blood vessels.
INVESTIGATIONS
Clinical examination by a dermatologist.
The diagnostic test is skin biopsy.
Pigmented basal cell carcinoma
SIGNS / SYMPTOMS
Basal cell carcinoma will have a pearly appearance with less pigmentation than typical melanoma.
In addition, there are prominent branching telangiectatic vessels in basal cell carcinoma. On dermoscopic evaluation, leaf-like areas of pigmentation and arborising blood vessels.
INVESTIGATIONS
Clinical examination by a dermatologist.
The diagnostic test is skin biopsy.
Pigmented actinic keratosis
SIGNS / SYMPTOMS
Pigmented actinic keratoses demonstrate more hyperkeratosis and erythema than melanoma, with less pigmentation, and tend to be somewhat smaller in size.
Pain may be associated with pigmented actinic keratoses.
INVESTIGATIONS
Clinical examination by a dermatologist.
The diagnostic test is skin biopsy.
Dermatofibroma
SIGNS / SYMPTOMS
Dermatofibroma demonstrates skin dimpling on palpation and a scar-like appearance, and is typically localised to the extremities only.
INVESTIGATIONS
Clinical examination by a dermatologist.
The diagnostic test is skin biopsy.
Subungual haematoma
SIGNS / SYMPTOMS
Instead of a longitudinal band, often associated with a subungual melanoma, a subungual haematoma appears as reddish-black globules of pigment that grow out distally as the nail grows.
In addition, the patient may be able to give a history of prior trauma.
Subungual melanoma may demonstrate pigmentation extending onto the proximal nail fold (Hutchinson's sign), unlike a subungual haematoma.
INVESTIGATIONS
Clinical examination by a dermatologist.
The diagnostic test is biopsy of the nail matrix.
Intracorneal haematoma
SIGNS / SYMPTOMS
Haemorrhage in the stratum corneum may be accompanied by a history of trauma.
INVESTIGATIONS
The pigment can be pared away with a scalpel blade.
Tinea nigra
SIGNS / SYMPTOMS
Superficial infection of the stratum corneum that typically appears on the palmar surface of the hands or feet. Usually not itchy. More homogenous pigmentation is seen than in melanoma.
INVESTIGATIONS
The pigment can be pared away with a scalpel blade.
Potassium hydroxide microscopic examination.
Fungal culture.
Pyogenic granuloma
SIGNS / SYMPTOMS
A lobular haemangioma most commonly seen in children. A mucosal form (usually affecting the maxillary mucosa or the inner nose) is commonly seen in pregnant women.
A new lesion is typically bright red in colour, which pales to a fleshy pink colour with time.
INVESTIGATIONS
The diagnostic test is skin biopsy.
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