Veterinary Guide to Canine Immune‑Mediated Polyarthritis (IMPA) 2025 🩺🐶

By Dr. Duncan Houston BVSc

🧬 What Is IMPA?

Immune‑mediated polyarthritis (IMPA) is a group of immune‑driven conditions where inflammation affects two or more joints due to immune complex deposition in joint tissues. It can lead to pain, swelling, fever, and systemic signs.

👥 Primary vs Secondary IMPA

• Primary IMPA (idiopathic): No identifiable trigger; most common form.
• Secondary IMPA: Triggered by underlying conditions including infections (UTI, tick‑borne diseases), neoplasia (e.g., lymphoma), gastrointestinal/liver disease, drug or vaccine reactions.

👀 Who Is at Risk & Clinical Signs

• Affects dogs aged 6 months to 12 years; both sexes are equally affected.
• Breed predisposition: Shar‑Pei, Akita, Beagle, Greyhound, Retrievers, Spaniels, Poodles.
• Signs include:
• Lameness affecting different legs at different times (shifting lameness)
• Joint pain, swelling or effusion—especially carpi, tarsi, stifles
• Fever, lethargy, decreased appetite—non‑specific systemic signs.

🔍 Diagnosis: Synovial Fluid & Exclusions

Diagnosis hinges on:

1. Synovial fluid analysis: Turbid, less viscous, WBC >3,000 cells/µL (especially non‑degenerate neutrophils) and protein >2.5 g/dL. Erosive forms may show cartilage/bone changes on x‑rays.
2. Baseline diagnostics: CBC (looks for inflammation, anemia), chemistry, urinalysis, 4Dx tick tests.
3. Imaging: Radiographs or ultrasound of chest/abdomen and joints to rule out neoplasia or infection.
4. Culture of joint fluid to exclude septic arthritis.
5. Rule out other immune diseases like SLE, tick‑borne illnesses, GI, or neoplastic triggers.

🛠️ Treatment Strategy

🏥 Hospital‑Phase Support

• Manage pain and fever—NSAIDs initially, but discontinue before corticosteroids.
• Address the underlying condition in secondary IMPA (e.g., antibiotics, tumor removal).

💊 Immunosuppressive Therapy

• Corticosteroids (prednisone/prednisolone): first-line; often high-dose for 2–4 weeks before gradual taper.
• Second-line agents for steroid-sparing or refractory cases: azathioprine (2 mg/kg EOD), ciclosporin (5 mg/kg BID), mycophenolate (10 mg/kg BID), leflunomide (2 mg/kg SID).
• Erosive IMPA (e.g., rheumatoid arthritis, greyhound form) requires long-term or lifelong therapy.

🧩 Adjunctive Therapies

• Pain relief: gabapentin or tramadol during tapering.
• Omega‑3 or PCSO‑524® joint supplements may reduce inflammation.
• Physical therapy or hydrotherapy for comfort and mobility.

📈 Monitoring & Follow‑Up

• Re-evaluate clinical signs and quality of life weekly to bi‑weekly early on.
• Perform repeat arthrocentesis before reducing medications; monitor synovial fluid changes.
• Use C‑reactive protein as a biomarker to gauge inflammation and remission.
• Monitor for drug side effects—CBC, chemistry, urinalysis every few weeks.

🔚 Prognosis

• Non‑erosive primary IMPA: Good to guarded—most dogs respond to treatment; relapses occur in ~15‑30%. Lifelong therapy may be needed.
• Erosive IMPA: Prognosis is poorer due to joint damage; therapy is often lifelong.
• Secondary IMPA: Outcome depends on treating the underlying cause—often good if resolved.

🏡 At‑Home & Lifestyle Management

• Keep the dog at a healthy weight to reduce joint stress.
• Provide soft bedding and low-impact exercise.
• Observe for swelling, lameness, fever—report early.
• Maintain follow‑up appointments and lab testing.

📱 Ask A Vet Telehealth Support

• Photo/video check‑ins: Send images of gait, posture, swelling to adjust meds remotely.
• Medication reminders: Alerts for prednisone tapering and immunosuppressive dosing.
• Lab alerts: Automated reminders for bloodwork and arthrocentesis.

🎓 Case Spotlight: “Luna” the Shar‑Pei

Luna, a 4‑year‑old Shar‑Pei, developed shifting lameness and high fever. Synovial fluid showed > 50k cells/µL and non‑degenerate neutrophils; 4Dx test was negative. Treated with high‑dose prednisone, then ciclosporin added. Joint fluid normalized by 6 weeks, prednisone tapered by 12 weeks, ciclosporin until 6 months. Luna remained symptom‑free 18 months later with low‑dose omega‑3 and Ask A Vet monitoring. 🐕❤️

🔚 Key Takeaways

1. IMPA is an immune‑mediated joint inflammation affecting multiple joints, which can be primary or secondary.
2. Diagnosis relies on synovial fluid analysis and ruling out infections or other systemic causes.
3. Treatment combines immunosuppression (steroids + adjuncts), supportive care & lifestyle adjustments.
4. Prognosis varies: primary non‑erosive form often has a favorable response; erosive or secondary depends on underlying causes.
5. Ask A Vet provides ongoing remote support—medication management, monitoring, nutrition—to maximize outcomes 📱

Dr Duncan Houston BVSc, founder of Ask A Vet. Download the Ask A Vet app today for expert telehealth support in managing your dog’s IMPA—guidance from diagnosis through long‑term remission! 🐾📲