What is your diagnosis for this lesion. The patient is a 30-year-old man who has had this asymptomatic lesion on his back since his childhood. No change in shape or color during recent years. No significant medical problems...

Diagnosis: Acantholytic Acanthoma

This condition usually occurs as a solitary papule or small nodule.

Histologically, acantholysis is the most prominent feature and may resemble pemphigus. Acantholysis may be combined with dyskeratosis as this case.