A 35-year-old man presents with painful swelling of his entire right index and ring fingers, as well as the fourth toe on his right foot, of 3 months' duration. He could not perform his daily activities because of severe pain in the affected fingers and toes. His medical history had been unremarkable except for strep throat 4 months ago, which resolved with antibiotic treatment. His paternal uncle had psoriasis and psoriatic arthritis (PsA), which was successfully treated with a biologic. This patient had no history of psoriasis.

Physical assessment revealed tender, fusiform, swollen soft tissues in the affected fingers, including the fingertips, the entire fourth toe, and swollen palms. The nails of the affected joints were separated from the nailbeds. The nails themselves showed pitting. Hand radiography revealed moderate edema of the soft tissue of the index and ring fingers, but no significant joint abnormalities.

Laboratory workup revealed negative rheumatoid factor (RF), serum urate of 3.5 mg/dL, C-reactive protein of 12 mg/L, and erythrocyte sedimentation rate of 85 mL/h. The patient was HLA-B27–negative.