A lesion present at birth due to proliferation of benign melanocytes is most consistent with which diagnosis?

• A. Cyst, sebaceous
• B. Congenital nevus
• C. Dermatitis herpetiformis
• D. Cutaneous candidiasis

Answer: (B)

A congenital nevus is a pigmented lesion present at birth caused by proliferation of benign melanocytes. Melanocytes come from neural crest cells, and during development a clone of these pigmented cells expands to form a well-circumscribed brown-to-black patch or plaque that is often flat but can be slightly raised. These lesions are generally benign, though the risk of melanoma increases with the size of the nevus, especially for large or giant congenital nevi, so larger lesions merit careful monitoring.

Sebaceous cysts arise from sebaceous glands and typically present as soft, movable nodules that are not pigmented from birth. Dermatitis herpetiformis involves intensely pruritic vesicles on extensor surfaces and is not a birth lesion. Cutaneous candidiasis presents with red, inflamed, sometimes macerated plaques or patches, not a stable pigmented birth lesion.