Erosive Immune-Mediated Polyarthritis in Cats: Vet Guide 🐱🩺 2025

By Dr Duncan Houston BVSc, veterinarian & founder of Ask A Vet.

Erosive immune-mediated polyarthritis (IMPA) is a rare, destructive form of arthritis where a cat’s immune system attacks joint cartilage and bone, especially in multiple joints. It leads to progressive pain, swelling, and lameness—early intervention is essential for comfort and mobility. This 2025 guide provides in-depth insights into:

• 🔍 What erosive IMPA is
• 🚨 Who’s at risk & clinical signs
• 🧪 Diagnostic workup including fluid testing and imaging
• 💊 Treatment strategies—immunosuppressants, supportive care
• 📆 Prognosis and long-term monitoring
• 🤝 Ask A Vet telehealth support

🔍 What Is Erosive IMPA?

This subtype of IMPA causes immune-mediated destruction of joint cartilage and underlying bone—visible on X-rays as erosions or soft tissue swelling. Unlike non-erosive forms, erosive IMPA is progressive and can significantly damage joints over time :contentReference[oaicite:2]{index=2}.

🚨 Who’s at Risk & Common Signs

• Seen in younger to middle-aged male cats (1.5–4.5 yrs), often idiopathic :contentReference[oaicite:3]{index=3}.
• Feline leukemia (FeLV), syncytia-forming virus (FSFV/feline calicivirus) may trigger cases :contentReference[oaicite:4]{index=4}.
• Signs include shifting-leg lameness, joint pain, swelling, fever and lethargy :contentReference[oaicite:5]{index=5}.
• Subtle onset: stiffness after rest, reluctance to move, muscle wasting :contentReference[oaicite:6]{index=6}.

🧪 Diagnostic Work-Up

Confirming erosive IMPA requires thorough investigation:

1. History & physical exam: assess multiple joints (stifles, hocks, carpi); evaluate for swelling and crepitus :contentReference[oaicite:7]{index=7}.
2. Bloodwork: CBC, chemistries, urinalysis, FeLV/FIV, calicivirus screening :contentReference[oaicite:8]{index=8}.
3. Imaging: X‑rays reveal bone erosions, joint effusion, soft tissue swelling and periostitis :contentReference[oaicite:9]{index=9}.
4. Synovial fluid analysis: arthrocentesis from ≥2–3 joints; look for neutrophilic inflammation without bacteria :contentReference[oaicite:10]{index=10}.
5. Biopsy: synovial or joint tissue when imaging uncertain :contentReference[oaicite:11]{index=11}.

💊 Treatment Strategies

1. Immunosuppressive Therapy

• Prednisolone: first-line, high-dose (≈2 mg/kg/day), taper per response :contentReference[oaicite:12]{index=12}.
• Cyclosporine (CsA): useful when tapering steroids; second-line immune modulator :contentReference[oaicite:13]{index=13}.
• Leflunomide or chlorambucil: added if response incomplete :contentReference[oaicite:14]{index=14}.
• Mycophenolate mofetil (MMF): new option—successful in one feline case, allowed steroid withdrawal with long-term control :contentReference[oaicite:15]{index=15}.

2. Supportive & Adjunctive Care

• Analgesia: NSAIDs (e.g., meloxicam) if no infection risk; consider opioids or gabapentin :contentReference[oaicite:16]{index=16}.
• Physiotherapy: gentle exercise, range-of-motion, massage, possible splints :contentReference[oaicite:17]{index=17}.
• Weight management: maintain muscle and minimize joint load :contentReference[oaicite:18]{index=18}.
• Taper medications slowly with periodic joint fluid checks :contentReference[oaicite:19]{index=19}.

📆 Prognosis & Monitoring

• Prognosis is guarded—70% respond well to therapy; recurrence is common :contentReference[oaicite:20]{index=20}.
• Relapses require adjusting medications; early treatment improves outcomes :contentReference[oaicite:21]{index=21}.
• Longevity: with control and monitoring, many cats maintain good quality of life long-term :contentReference[oaicite:22]{index=22}.
• Monitor with rechecks: physical exam, joint fluid cytology, radiographs every 3–6 months.

🛡️ When to Seek Help

• Signs of non-response or relapse: increased lameness, swelling, fever
• Side effects: polyuria/polydipsia, GI upset, infection risk
• Infection or gastrointestinal complications—may need adjustments in therapy
• Degenerative changes may need orthopedic assessment

🤝 Ask A Vet Telehealth Support

• 📸 Review pictures of swollen joints and gait for monitoring
• 💬 Assist in monitoring medication side effects and tapering schedule
• 🗓 Help decide on recheck timing, joint taps or imaging needs
• 🏥 Recommend when in-clinic treatment is essential
• 📈 Support through flare-ups or slow relapses

✅ Key Takeaways

• Erosive IMPA is a rare but serious autoimmune arthritis in cats, causing joint destruction
• Diagnosis via joint fluid analysis and imaging; exclusion of infections or cancer is essential
• First-line therapy with steroids; adding CsA, leflunomide, or MMF may be necessary
• Supportive care—pain relief, rehab and weight control—are vital
• With timely treatment, many cats maintain mobility and comfort long-term
• Ask A Vet telehealth ensures guidance from diagnosis through maintenance

📞 Final Thoughts

Erosive IMPA demands a proactive, multi-modal approach. Early diagnosis, targeted immunosuppression, and supportive care dramatically enhance outcomes. With Ask A Vet’s telehealth guidance, you’ll be supported through every decision—helping your cat live with ease, comfort, and mobility. 😊🐾

Concerned your cat may have joint swelling, shifting-leg pain or fever? Visit AskAVet.com and download the Ask A Vet app for personalized telehealth support anytime!