Immune-Mediated Polyarthritis in Dogs: Diagnosis and Long-term Management

Immune-mediated polyarthritis causes fever, joint pain, and mobility impairment in dogs, requiring accurate diagnosis to distinguish from infectious and neoplastic causes.

Key Facts

IMPA affects multiple joints simultaneously, most commonly the carpi, tarsi, and stifles
Clinical signs include fever, shifting leg lameness, reluctance to move, and joint swelling
Cytology of synovial fluid shows inflammatory cells confirming joint disease
Idiopathic IMPA (Type I) is most common and responds well to immunosuppression
Reactive IMPA (Type II) is secondary to distant infection or inflammation requiring treatment of the primary source
Erosive IMPA (rheumatoid-like) causes progressive joint destruction and carries a guarded prognosis
Prednisolone is first-line treatment with response expected within 2-4 weeks

Welfare Considerations

Immune-mediated polyarthritis causes significant suffering - dogs in active disease show obvious pain, fever, and profound reluctance to move or be handled. The multi-joint nature means there is no comfortable position, and fever adds systemic debility. The condition is often misdiagnosed or treated empirically without synovial fluid analysis, delaying appropriate management. Accurate diagnosis enables appropriate immunosuppression that resolves joint inflammation and allows return to near-normal activity. Long-term management and monitoring for relapse are essential - relapses cause renewed suffering that can be minimized by early detection and treatment adjustment.

What You Can Do

Seek joint fluid analysis if your dog shows fever with shifting lameness in multiple joints
Request complete blood count, biochemistry, and infectious disease screening to rule out reactive causes
Begin prednisolone as directed and monitor for response within 2-4 weeks
Add azathioprine or leflunomide if prednisolone alone provides inadequate control
Taper immunosuppression gradually over months based on clinical response
Monitor for relapse when medications are reduced - early recognition enables prompt retreatment
Investigate for underlying infections or inflammatory conditions in dogs with reactive IMPA