Herpes Simplex Virus Proctitis Masquerading as Rectal Cancer.

Herpes simplex virus (HSV) is the leading cause of proctitis in HIV-infected individuals. However, no cases of rectal masses secondary to HSV infection have been reported to date. Herein, we present the case of a 45-year-old man with HIV infection who developed rectal pain and bleeding, along with dysuria and voiding difficulty. Colonoscopy revealed proctitis and a rectal mass with features concerning for rectal cancer. Histologic sections of the rectal mass biopsy demonstrated colorectal mucosa with viral cytopathic changes, ulceration, granulation tissue, marked inflammatory infiltrate, and fibrinopurulent exudate. Immunohistochemistry for herpes simplex virus-1 was positive in epithelial cells demonstrating a viral cytopathic effect. The patient was treated with valacyclovir for 3 weeks, which led to complete resolution of his symptoms. Follow-up sigmoidoscopy at 6 months did not show any masses. Our case illustrates the importance of considering HSV in the differential diagnosis of rectal masses. We advocate the routine use of viral immunohistochemistry for the evaluation of rectal tumors, especially in patients with clinical manifestations and endoscopic findings consistent with proctitis.