Differentials of malignant melanoma

Malignant melanoma

This patient had noticed the mole on his chest about two months before. He was concerned because it had increased in size and recently had begun to itch and had bled. On examination there was an irregularity of the edges of the lesion with slight colour variation. The central area showed a red colour with areas of ‘milky blue’, a broadened network, radial streaming and multiple brown and blue-grey dots.

Black heel syndrome

This patient was a keen footballer and presented with an irregular dark macule over the heel. Black heel syndrom is usually seen in teenagers and young adults who are involved in sports where there is shearing of the epidermis over the dermis, resulting in intraepidermal haemorrhage.

Shaved fragments of keratin can be examined for occult blood. The lesion may clear on shaving, whereas melanocytic lesions retain their pigment. If still in doubt, a biopsy should be taken. No treatment is required.

Blue naevus

Blue naevus may appear at any age but is most commonly seen in older children and adolescents. Usually it is less than 0.5mm in diameter. The lesions occur most often on the face, and backs of the hands and feet.

Under the dermatoscope a homogeneous blue pigmentation is seen throughout the lesion. No treatment is required but, if the patient wishes, it may be excised under local anaesthetic for cosmetic reasons.

Lentigio maligna

Lentigo maligna (Hutchinson’s freckle) usually presents on the face or neck of the elderly who have experienced considerable sun exposure. It is a flat, brown or black macule with irregular margins that grows slowly. It is a premalignant lesion and a biopsy should be taken. Treatment options include cryotherapy, imiquimod or excision.

Pigmented basal cell carcinoma

This patient developed a cystic, pigmented lesion on the scalp. It had been growing slowly for some months and was  bleeding when the patient combed her hair.

The diagnosis is basal cell carcinoma. Typical features are arborising vessels, maple leaf like areas, large blue-gray globules, ovoid nests and spoke wheel areas. If in doubt the lesion should be biopsied and/or excised.

Dermatofibroma 

Dermatofibromas present as firm nodules that may have a yellow/brown appearance. In patients with dark skin they may be darker. The lesions are most often seen on the limbs and tend to arise at the site of some minor injury, such as an insect bite. On examination the firm nodule is tethered to the skin and dimples when squeezed. Once formed, it may persist for years. Treatment is unnecessary but if in doubt it can be excised and examined histologically.

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