Secondary Syphilis in the Spotlight: Atypical Cutaneous Manifestation Overshadowing Kaposi Sarcoma in a Newly Diagnosed HIV Patient

Syphilis, caused by the spirochete <i>Treponema pallidum</i>, is a sexually transmitted infection (STI) that has seen a resurgence worldwide, particularly among populations at a higher risk of co-infection with human immunodeficiency virus (HIV). The disease typically progresses through distinct stages: primary, secondary, latent, and tertiary, each with specific clinical manifestations. Secondary syphilis is characterized by systemic involvement and various mucocutaneous symptoms, including a maculopapular rash that frequently involves the palms and soles along with fever, lymphadenopathy, and mucous membrane lesions. However, in patients with HIV co-infection, syphilis may present atypically. The immunosuppression caused by HIV can lead to more severe, atypical, and persistent manifestations of secondary syphilis. Furthermore, the cutaneous features may deviate from the classic presentation, making diagnosis challenging. We report the case of a male in his third decade of life, recently diagnosed with HIV, who presented with diffuse hyperpigmented dermatosis. The unusual presentation, including well-defined brown macules with a generalized distribution, initially raised suspicion for Kaposi's sarcoma (KS), a frequent cutaneous malignancy seen in HIV patients. Skin biopsy showed a dense perivascular and interstitial inflammatory infiltrate with marked endothelial swelling and vascular proliferation. Immunohistochemistry confirmed the presence of <i>Treponema</i> spirochetes, and a positive Venereal Disease Research Laboratory (VDRL) test further supported the diagnosis of secondary syphilis in the context of HIV. Our case underscores the importance of considering secondary syphilis in the differential diagnosis in cases of generalized hyperpigmented dermatosis in newly diagnosed HIV patients, where common conditions such as Kaposi's sarcoma may obscure the underlying etiology.