Coccidiomycosis septic arthritis presenting as ankle monoarthritis in a patient with presumed psoriatic arthritis

A man in his 50s with a history of psoriasis was evaluated for acute on chronic left ankle pain. His symptoms were attributed to psoriatic arthritis, and he tried several immunosuppressive regimens without improvement. Further diagnostic workup confirmed <i>Coccidioides immitis/posadasii</i> septic monarthritis thought secondary to a known remote history of Valley fever while residing in Arizona and subsequent reactivation in the setting of immunosuppression. The patient ultimately required prolonged anti-fungal therapy and multiple surgical debridements.Although psoriatic arthritis can present as monarthritis, it is uncommon, with more likely differential considerations including crystal arthropathies, trauma and both typical and atypical infections. Acute monarthritis should always prompt concern for a septic joint, even in a patient with autoimmune disease. The specific history elicited from the patient, including residence in an endemic region, and known prior <i>Coccidioides</i> infection, increased suspicion for <i>Coccidioides</i> and led to the correct diagnosis and management.