A rare case of amelanotic anorectal melanoma.

We report an exceedingly rare case of amelanotic anorectal melanoma misdiagnosed as hemorrhoids. A 74-year-old man presented with a week's history of "blood on toilet tissue" without bowel complaints or history of cutaneous melanoma. Skin evaluation was normal. Rectal exam was negative for blood, but revealed an anal nodule, interpreted as a hemorrhoid. Hemoglobin was normal; bleeding persisted. After one month, colonoscopy detected a non-pigmented anal lesion. Biopsy showed melanoma. Noncutaneous mucosal melanoma represents 0.03% of new cancer diagnoses Anorectal melanoma accounts for 1% of melanomas and 0.4% of anal malignancies. Uncommonly, this malignancy lacks melanin pigment, complicating detection. Presenting complaints are non-specific rectal bleeding, pain, itching or incontinence, mimicking more common disorders. Dangerous misdiagnosis occurs when benign disease, not malignancy, is suspected. Risk factors for cutaneous melanoma are less frequent. Mucosal melanoma has different genetics. Clinicians must be aware of diagnostic difficulties of anorectal melanoma, especially when amelanotic. [Full article available at http://rimed.org/rimedicaljournal-2017-09.asp].