Malignant syphilis requiring differentiation from Kaposi's sarcoma.

Malignant syphilis (MS) is a rare variant of secondary syphilis. Also known as rupioid syphilis, MS is characterized by the presence of multiple papules, papulopustules, black lamellate crust that may resemble an oyster shell, or nodules with ulceration lacking central clearing. MS is often associated with immunodeficiency and frequently co-occurs with HIV infection. We here report a case of MS in a patient with HIV infection. HIV infection can cause atypical clinical symptoms of syphilis. In this case, unlike previous cases, cutaneous lesions of MS were limited to the face, making the diagnosis challenging based on clinical findings alone. However, his laboratory findings, appearance of the Jarisch-Herxheimer reaction, and a dramatic response to antibiotic therapy are characteristic of MS, making the diagnosis even more certain. Our case suggests the importance of physicians considering the possibility of MS when observing black-crusted lesions.