Acute Human Immunodeficiency Virus Infection Concurrent With Mpox Presenting With Proctitis and Disseminated Skin Lesions: A Case Report.

Background: The concurrent presentation of mpox and acute human immunodeficiency virus (HIV) infection is uncommon and may be difficult to recognize because the two conditions share nonspecific early manifestations, including fever, rash, lymphadenopathy, and pharyngeal symptoms. Mpox-associated anorectal disease may further complicate diagnosis when patients initially present with severe anal pain or proctitis-like findings. Case Presentation: A previously healthy 29-year-old Japanese man presented with fever, malaise, severe anal pain, and disseminated pustular skin lesions. He initially visited a specialized proctology hospital, where lower endoscopic examination demonstrated circumferential ulceration extending from the dentate line into the anal canal, erythematous and edematous rectal mucosa, and firm circumferential submucosal induration. The anorectal lesion was initially considered to represent a hemorrhoidal fistula. He subsequently visited the emergency department and received valacyclovir for suspected herpes simplex virus infection before referral to the infectious diseases department. Mpox was confirmed by polymerase chain reaction testing of skin lesions. In addition, monkeypox virus DNA was detected in the anorectal biopsy specimen, and immunohistochemical staining demonstrated viral antigen in the tissue. HIV testing showed a reactive fourth-generation antigen/antibody screening assay, a negative HIV-1/2 antibody differentiation assay, and a plasma HIV RNA level of 7.9 × 10 Conclusion: Concurrent acute HIV infection and mpox can present with overlapping systemic, cutaneous, and anorectal manifestations. This case highlights the importance of integrating lesion morphology, anorectal findings, epidemiological history, and virological testing when evaluating patients with suspected sexually transmitted viral infections.