How would you diagnose this mystery lesion?

A 55-year-old male presented for his annual skin examination, which revealed an asymptomatic lesion on his back. It is of unknown duration as the patient was unaware of it. He had recently returned from extended travel overseas in Asia. He is otherwise healthy.

How would you diagnose his mystery lesion?

A. Insect bite reaction
B. Nummular eczema
C. Basal cell carcinoma
D. Amelanotic melanoma 
E. Melanoma
F.  Lichenoid keratosis

(Answer and discussion on next page)

Answer: Amelanotic melanoma

A biopsy showed this to be a 0.4 mm amelanotic melanoma. Amelanotic melanoma is extremely difficult clinical diagnosis to make as demonstrated by this case. All of the differential diagnoses are reasonable, which made biopsy necessary to confirm the clinical diagnosis (not suspected prior to the biopsy). This also supports the importance of yearly physical examinations, action that was recently—and questionably—criticized by an academic physician in these 2 New York Times columns: “Skip Your Annual Physical” (Emanuel, EJ, Op-Ed, January 9, 2015) and “Your Annual Checkup” (Letters to the Editor, January 17, 2015).