A patient with a history of intravenous drug use presents with bleeding gums and purpuric mucosal lesions. What is the most likely underlying cause?

Correct answer: D. HIV infection

• A. Marrow failure from an injected contaminant is possible but far less likely than the well-established HIV association.
• B. Haemophilia A is an X-linked inherited disorder that would have presented in childhood and is unrelated to intravenous drug use.
• C. Vitamin K deficiency causes bleeding but not the purpuric mucosal lesions described, and there is nothing in the history pointing to malabsorption or prolonged antibiotic use.
• D. CORRECT per the source key. Intravenous drug use is a major risk factor for HIV transmission. Purpuric mucosal lesions in this context raise both HIV-associated thrombocytopenia, which explains the bleeding gums and purpura directly, and Kaposi sarcoma, which produces purple-red macular and nodular mucosal lesions.

Note: ⚑ Leukaemia is a genuinely reasonable differential here — gingival bleeding, mucosal purpura and gingival enlargement are classic presenting features of acute leukaemia, and dentists do diagnose it. The intravenous drug use history is what tips the balance toward HIV in this stem. Either way, the action is the same: refer urgently for a CBC with differential and appropriate serology.