Intra-articular organisms are not always cytologically detectable in dogs with blastomycosis-associated inflammatory arthritis

Objective To describe the clinical, cytologic, and radiographic features of inflammatory arthritis associated with blastomycosis in dogs. Methods This study included 12 dogs with blastomycosis and cytologic evidence of inflammation in at least 1 joint identified at a tertiary referral center over a 25-year period. Median age of presentation was 5.0 (1.1 to 9.0) years, and 4 of 12 cases were Labrador Retrievers. Musculoskeletal signs were the primary complaint for 10 dogs, while the other 2 presented for respiratory concerns. All dogs were lame upon evaluation, and 10 of 12 had palpable joint swelling. All dogs had evidence of blastomycosis in at least 1 other body system. Results Of 25 joint fluid cytologies, interpretations consisted of inflammatory arthritis in 21 joints (12 dogs), degenerative joint disease in 1 joint (1 dog), and unremarkable in 3 joints (2 dogs). The inflammation was categorized as suppurative (17 joints, 11 dogs) or pyogranulomatous (4 joints, 1 dog). Intra-articular Blastomyces organisms were observed in 10 joints (6 dogs). Eight of 9 joints (7 of 8 dogs) imaged had at least 1 radiographic abnormality, including 5 joints with osteolytic lesions. All bony lesions were periarticular. Ten dogs received oral antifungal drugs. Three dogs died within 1 month of evaluation; all 6 dogs with long-term follow-up achieved blastomycosis remission, but 2 required surgical arthrodesis of affected joints. Conclusions Not all dogs with blastomycosis-associated arthritis have cytologically detectable organisms in their joint fluid. Clinical Relevance Unlike other sampling sites where pyogranulomatous inflammation predominates, suppurative inflammation is most common in the joints.