免疫抑制患者における悪性腫瘍を模倣した播種性腹膜コクシジオイデス症：症例報告

Disseminated peritoneal coccidioidomycosis is rare and can mimic peritoneal carcinomatosis. Ustekinumab, an IL-12/23 inhibitor, impairs Th1/Th17 immunity which is critical for fungal control. No prior cases link ustekinumab use to disseminated fungal disease. We report a 45-year-old woman from an endemic region with prior pulmonary coccidioidomycosis and psoriatic arthritis on ustekinumab who presented with malignant-appearing ascites and omental caking. Fluid studies were non-diagnostic, but laparoscopic biopsies confirmed disseminated Coccidioides infection. She improved with liposomal amphotericin B followed by oral fluconazole suppression. This case highlights the need to consider peritoneal coccidioidomycosis in immunosuppressed patients, particularly on IL-12/23 blockade, and underscores the role of tissue diagnosis when fluid studies are negative.