Workup for STIs is negative—how do you explain this penile lesion?

Case: A 24-year-old man seeks evaluation of a rash on his penis; it is associated with mild burning on urination. Workup for gonococcal and chlamydial infection is negative. He is otherwise healthy.

What is the most likely cause of the rash?

A. Candida balanitis.
B. Herpes simplex.
C. Lichen planus.
D. Zoon balanitis.
E. Bowenoid papulosis.

A biopsy confirmed the diagnosis of balanitis circumscripta plasmacellularis, or Zoon balanitis, D. This is an idiopathic, rare, benign penile dermatosis.

Proposed causative or predisposing factors include friction, trauma, heat, poor hygiene, chronic infection with Mycobacterium smegmatis, a reactive response to an unknown exogenous or infectious agent, an immediate hypersensitivity response mediated by IgE antibodies, and hypospadias.¹

The diagnosis of Zoon balanitis is made by biopsy. The dermatosis has been treated successfully with tacrolimus ointment.

Candida balanitis features more scale than this patient’s rash, and herpes simplex lesions are vesicular. Lichen planus is characterized by flat purple polygonal papules, and bowenoid papulosis consists of lightly pigmented flat papules.