In Diagnosing Acral Melanoma: A Case of Synergistic Subtleties

Summary: An 81-year-old gentleman presented for evaluation of a chronic toenail lesion. On examination, an area on the plantar foot was incidentally noted to have a subtle mottled patch of dyspigmentation. Shave biopsy revealed a junctional and suprabasilar proliferation of small single and nested melanocytes associated with elongated rete with a small focal dermal component. MART and SOX10 did not reveal prominent pagetoid scatter or confluence. The melanocytes expressed PRAME. Correlating histology with the broad area of discoloration confirmed a diagnosis of melanoma. Excision showed acral lentiginous melanoma in situ (ALMIS) extending to margins, requiring two Moh stages for clearance. This case highlights the importance of clinicopathologic correlation in evaluating acral melanocytic lesions. Early ALMIS diagnosis is challenging: acral nevi exhibit pagetoid scatter that may overlap with melanoma, thus, these findings are downplayed on acral pigmented lesions; and cytologic atypia may be lacking in early ALMIS. This case demonstrated histopathologic features that can be seen in acral nevi, and while the lesion lacked overt clinically malignant features, coupling the histology with the large area of subtle discoloration helped to confirm a melanoma diagnosis. Additionally, this case demonstrates that PRAME can be a helpful adjunct to differentiate acral melanoma from acral nevi.