Amelanotic melanomas contribute to 8% of melanomas, and usually are pink, pale or skin coloured, more symmetrical, and found to be more associated with nodular and unclassified histologic subtypes.1 A literature review conducted revealed only four reported amelanotic melanomas appearing hypopigmented or depigmented and out of them only two were patches. We present a rare case of amelanotic melanoma appearing as a hypopigmented patch which was previously diagnosed as vitiligo, resulting in a delayed diagnosis.
A 58-year-old male visited the dermatology department for a full skin examination with a family history of melanoma and a personal history of non-melanoma skin cancers since age eighteen. He has no personal history of melanoma, but his mother and sister are known to have melanoma. His only other medical history is Wilson's disease with associated cirrhosis. On examination, he had a well circumscribed annular hypopigmentated patch on his upper arm amongst a few other lesions.
Histopathology report showed an intraepidermal proliferation of singly dispersed mildly atypical cells that have enlarged slightly irregular hyperchromatic nuclei with intranuclear pseudo inclusions and distinct nucleoli. There is pagetoid spread, but no dermal invasion. These cells show positive immunostaining with the melanocytic markers SOX10 and HMB45 while broad spectrum cytokeratin AE1/3 is negative. The features are consistent with melanoma in situ.
This case highlights the need to be weary of amelanotic melanoma as a differential for hypopigmented patches.