Cross-Reactivity of Urinary Histoplasmosis Antigen With Disseminated Sporotrichosis in a Patient Living With Hiv/AIds

Sporotrichosis is an endemic mycosis with global distribution, caused by Sporothrix spp., ubiquitous fungi found in vegetation, organic matter, and soil. In immunocompetent individuals, it usually results in localized disease, presenting as cutaneous or lymphocutaneous forms. However, in immunosuppressed patients, such as people living with HIV/AIDS, or depending on inoculum size, it may lead to disseminated disease. To report a case of disseminated sporotrichosis in a patient living with HIV/AIDS with probable cross-reactivity of the histoplasmosis antigen test. A 43-year-old male patient, diagnosed with HIV two months earlier (initial CD4 count of 32 cells/mm³), pulmonary tuberculosis also diagnosed two months earlier, and clinical-epidemiological diagnosis of disseminated sporotrichosis four months prior (the patient reported being scratched by his cat, which later died of sporotrichosis). He was already receiving itraconazole 200 mg/day, tenofovir + lamivudine + dolutegravir, with a most recent viral load of 856 copies/mL and CD4 count of 120 cells/mm³, and was on rifampicin. He was admitted to an infectious diseases ward due to worsening ulcerative-crusted lesions on the upper limbs, generalized lymphadenopathy, and a new pulmonary infiltrate. Skin lesion biopsies were performed, and histopathology revealed numerous yeasts with a report suggestive of histoplasmosis; therefore, a urinary histoplasma antigen test was requested and resulted weakly positive. However, other histoplasmosis investigations (serum PCR and antibodies) were negative, and culture of skin lesion fragments showed growth of a filamentous fungus identified as Sporothrix spp. Disseminated sporotrichosis was therefore confirmed, and liposomal amphotericin B at 300 mg/day was initiated, with marked clinical improvement of the lesions. Cross-reactivity of the urinary histoplasmosis antigen is described in package inserts but is rarely reported in the literature, with few documented cases. In the present case, cross-reactivity with Sporothrix spp. was observed, which should be considered, as both mycoses may cause cutaneous lesions and disseminated disease in patients with severe immunosuppression.