Severe Anorectal Mpox With Newly Diagnosed HIV and Syphilis: A Diagnostic and Management Challenge.

Mpox has re-emerged globally in non-endemic regions, challenging clinicians with diverse mucocutaneous manifestations that frequently mimic other sexually transmitted infections (STIs). Early genital and anorectal lesions may resemble herpes simplex virus or syphilis, often resulting in diagnostic error and treatment delay. Lesion distribution frequently corresponds to the route of transmission, further complicating clinical recognition. We describe a 25-year-old male who presented with diffuse pustular and vesicular eruptions, including extensive anorectal and genital involvement, confirmed as Mpox by polymerase chain reaction (PCR) testing. Additional evaluation revealed previously undiagnosed HIV infection with marked immunosuppression and latent syphilis. This case underscores the diagnostic complexity and therapeutic urgency of Mpox in patients with concurrent STIs and highlights the necessity of comprehensive sexual-health screening, early antiviral initiation, and multidisciplinary management during ongoing outbreaks.