Type I idiopathic non-erosive immune-mediated polyarthritis in a mixed-breed dog.

A young adult dog was presented with an acute onset of stiffness, weakness, marked muscle atrophy and rapid weight loss. The dog was inappetent, lethargic, and had grossly visible distension of multiple joints. Synovial fluid analysis, routine bloodwork, and radiography confirmed immune-mediated polyarthritis; the dog responded favorably to treatment with prednisone and analgesics.