How to Differentially Diagnose Melanoma

The differential diagnosis includes basal cell carcinoma, seborrheic keratosis, dysplastic nevus, blue nevus, dermatofibroma, various types of nevus, hemangioma (especially on the hands and feet), venous lakes, pyogenic granulomas, and warts. If in doubt, a full-thickness skin biopsy slightly beyond the lesion must be performed. Excisional biopsy is performed for small lesions and incisional biopsy is performed for larger lesions. Serial biopsies can determine the depth of invasion of melanoma, and complete radical surgery must be performed only after a clear histological diagnosis.

Criteria for excision or biopsy of pigmented lesions include recent enlargement, darkening, bleeding, or ulceration. However, these symptoms often indicate that melanoma has invaded deeper into the skin. When a lesion changes color (such as brown or black mixed with a red, white, or blue background), irregular ridges can be seen or touched, and the edges are angular or notched, the lesion should be biopsied immediately to make an early diagnosis. Examination of pigmented lesions with a dermatoscope (a modified oil-immersion spectacles) can help distinguish melanoma from benign lesions.

Treatment and prognosis are determined primarily by microscopic observation of the depth of invasion of the melanoma. Histological grading requires an adequate biopsy. Central nervous system and subungual melanomas are generally not classified using these systems.

The depth of lymphocyte infiltration reflects the patient's immune response system and is related to the degree of infiltration and prognosis. If lymphocytes infiltrate only in most superficial lesions, the chance of cure is greater. Conversely, as the depth of infiltration increases, the chance of cure decreases significantly.