A 30-year-old man comes to the office for evaluation of 2 months of lower-extremity swelling and skin lesions. He has no shortness of breath, fever, night sweats, or abdominal pain. He has had some weight loss but is unable to quantify the exact amount. The patient is an ex-intravenous drug user and was hospitalized 3 years ago for upper-extremity cellulitis. Three months ago, he went to an urgent care clinic for white patches in his mouth. His temperature is 37.2 C (99 F), blood pressure is 132/78 mm Hg, and pulse is 92/min. His BMI is 22 kg/m². Skin examination of the groin region is shown below. Which of the following is the most likely diagnosis?

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This patient's recent oral infection (likely thrush) and history of intravenous drug use suggest HIV. His skin lesions are consistent with AIDS-related Kaposi sarcoma (KS), an AIDS-defining illness (due to human herpesvirus 8) seen predominantly in men who have sex with men. Cutaneous KS develops most often on the lower extremities, face, oral mucosa, and genitalia. The lesions commonly appear as multiple violaceous (or pink, red, brown) papules due to increased vascularity. Patients do not usually have significant pruritus or skin necrosis. Prominent lymphedema (due to vascular obstruction by KS lesion or to cytokine production), which can manifest as extremity swelling, can sometimes be seen. Opportunistic infections in HIV (eg, oral thrush) increase proinflammatory cytokines and can significantly increase the risk of KS development or exacerbation. Diagnosis is made clinically, although patients with atypical lesions or systemic symptoms may require biopsy to exclude other causes (eg, bacillary angiomatosis due to Bartonella). KS can also involve the gastrointestinal tract and other organ systems. Treatment is with antiretroviral therapy and, in advanced cases, chemotherapy. (Choice A) Condyloma acuminata (anogenital warts) is due to human papillomavirus. Patients typically develop skin-colored, whitish, or grayish (not violaceous) verrucous and filiform papules in the anal/perianal area (more often in men), penile shaft, or vulvovaginal and cervical areas. Lymphedema is uncommon. Condyloma acuminata (Choice C) Leukocytoclastic vasculitis can be due to infections, medications, inflammatory conditions, or malignancy. It typically presents as non-blanching, 1-3 mm violaceous papules that can cluster/coalesce into plaques. Older lesions appear brownish-red; newer ones are more violaceous. Leukocytoclastic vasculitis (Choice D) Malignant melanoma can be a life-threatening malignancy derived from melanocytes, either de novo or from a previously existing pigmented lesion. Melanomas can occur on the skin or mucous membranes. Patients usually develop pigmented lesions with "ABCDE" features of melanoma: Asymmetry, irregular Borders, multiple Colors, Diameter >6 mm, and Evolution. Malignant melanoma > (Choice E) Neurofibromatosis type 1 typically presents with widespread subcutaneous nodules associated with multiple café-au lait spots. Neurofibromatosis type 2 can present with a vestibular schwannoma and raised plaque-like lesions or subcutaneous nodules (from nerve swelling). Neurofibromatosis type 1 café-au lait spots Educational objective: HIV-associated Kaposi sarcoma (KS) is an AIDS-defining malignancy due to human herpesvirus 8. Cutaneous KS develops most commonly on the lower extremities, face, oral mucosa, and genitalia. The lesions usually appear as multiple violaceous papules. Diagnosis is made clinically but may require biopsy. References: HIV-associated Kaposi sarcoma: pathogenic mechanisms. (http://www.ncbi.nlm.nih.gov/pubmed/17142074) Kaposi sarcoma: review and medical management update. (http://www.ncbi.nlm.nih.gov/pubmed/22677687)

A 30-Year-Old Man Comes to the Office for Evaluation of 2