Differential diagnosis of subungual melanoma

The differential diagnosis of subungual melanoma is primarily based on observation of its size, color, surface characteristics, border clarity, and growth rate. Specifically: 1. Size: Subungual melanoma typically presents as a mole or pigmented spot with a diameter greater than 6 mm, significantly larger than non-melanoma skin cancers such as basal cell carcinoma (which usually appears as small lesions less than 5 mm). 2. Color: It may exhibit asymmetric color distribution, with one side darker than the other, differing from the uniform coloration commonly seen in non-melanoma skin cancers. 3. Surface characteristics: Subungual melanoma may show irregular shape, loss of normal texture, or abnormal vascular patterns, whereas non-melanoma skin cancers typically remain relatively flat with well-defined borders. 4. Border clarity: The borders are often irregular, blurred, or notched, in contrast to the neat, smooth edges characteristic of non-melanoma skin cancers.