Skeletal coccidioidomycosis: an atypical pediatric presentation.

Coccidioidomycosis is most commonly a self-limited pulmonary infection. Disseminated disease is rare, occurring in fewer than 1% of cases, with skeletal involvement representing an uncommon manifestation in children. We report a case of skeletal coccidioidomycosis in a previously healthy 12-year-old with pelvic involvement and no antecedent pulmonary symptoms. The patient presented with 1.5 months of progressive, atraumatic left pelvic pain, night sweats, and weight loss, without respiratory complaints. Radiographs demonstrated a lytic lesion of the left ilium extending toward the acetabulum, with ill-defined margins and prominent surrounding reactive sclerosis. Mineralized matrix production was absent. Magnetic resonance imaging revealed an extensive marrow-replacing lesion contiguous with a heterogeneous soft-tissue component exhibiting focal internal enhancement. The lesion demonstrated diffusion restriction, consistent with abscess formation, while the hip joint was preserved and there was no neurovascular involvement. Although these findings raised concern for malignancy, there were subtle infection-favoring features and subsequent biopsy was performed. Histopathology demonstrated fungal elements with associated giant cell reaction. The patient was treated initially with intravenous amphotericin B and transitioned to oral itraconazole following culture confirmation of Coccidioides, with a planned prolonged antifungal course. At 6-month follow-up, the patient had resumed full activity with complete resolution of pain and preserved pelvic function. This case highlights the importance of including coccidioidomycosis in the differential diagnosis of aggressive pediatric osseous lesions. Recognition of key imaging features, including lytic osseous destruction with surrounding sclerosis and a heterogeneous soft-tissue component with diffusion restriction, can facilitate timely diagnosis, prevent misdiagnosis, and reduce morbidity risk.