🦴 Vet-Approved Guide to Immune-Mediated Polyarthritis (IMPA) in Dogs (2025) 🐾

By Dr Duncan Houston BVSc

Immune-mediated polyarthritis (IMPA) is a condition where a dog’s own immune system attacks its joints, causing pain, lameness, and swelling across multiple joints 🦵. It can strike suddenly and affects dogs of all ages and breeds—especially young large-breed dogs and older small breeds 🐕. In this comprehensive 2025 veterinary guide, Dr Duncan Houston walks you through the signs, diagnosis, treatment, and long-term care for this complex immune disorder.

❓ What Is IMPA?

IMPA occurs when the immune system mistakenly identifies joint tissues as foreign and launches an inflammatory response, leading to joint swelling, heat, stiffness, and pain 🔥.

• 🧬 It is classified as an autoimmune condition
• 🔁 Can be triggered by infections, medications, or vaccines
• 👥 Can also occur with no known cause (idiopathic)

🧩 Two Major Forms:

• Non-Erosive IMPA: Most common; no joint damage
• Erosive IMPA: Rare; causes joint deformation (like rheumatoid arthritis)

📋 Common Signs of IMPA

Dogs affected by IMPA may show one or more of the following:

• 🐕 Reluctance to walk or stiffness, especially after rest
• 🔥 Warm, swollen, painful joints
• 🍽️ Decreased appetite or full anorexia
• 🥤 Increased thirst
• 🦠 Enlarged lymph nodes, lethargy, or fever

These signs may come and go or appear suddenly. If your dog seems sore in multiple joints or shows stiffness in the mornings, IMPA should be considered 🩺.

🧬 Types of Non-Erosive IMPA

Type I – Idiopathic

No underlying trigger is found. This is the most common form, affecting about 50–65% of cases.

Type II – Secondary to Infection

IMPA may develop as a result of an infection (e.g., tick-borne diseases). Immune complexes from the infection trigger joint inflammation.

Type III – Liver or GI Disease Related

Less common (about 5%). This form links to chronic digestive or liver disorders.

Type IV – Cancer Associated

Very rare (about 2%). Seen when a tumor elsewhere in the body indirectly stimulates joint inflammation 🧪.

🧬 Breed-Associated Cases

• 🐕 Akitas
• 🐶 Boxers
• 🐾 Spaniels
• 🟤 Weimaraners
• 🏔️ Bernese Mountain Dogs
• 🔁 Doberman Pinschers (especially with sulfa drug exposure)

📉 Erosive IMPA (Rheumatoid Arthritis)

This less common form affects about 1% of cases and causes actual joint damage 🧊. Small-breed, middle-aged dogs are most commonly affected, with wrists, knees, and toes most involved.

• 📸 X-rays may show “punched out” lesions like a golf ball dimple pattern
• 🕒 May not appear on radiographs early—repeat imaging is advised if signs persist

🔬 Diagnosing IMPA

🧪 Key Tools:

• 🩺 Full physical exam and joint assessment
• 💉 Bloodwork: detects anemia, inflammation markers
• 🧫 Joint taps (arthrocentesis): confirms joint inflammation and immune involvement
• 🦠 Tick testing and urinalysis to rule out secondary causes
• 📸 Imaging (X-rays, MRI): especially if erosive arthritis is suspected

Timing is crucial—tests are more reliable during flare-ups. Your vet may refer you to a veterinary internist for advanced testing 🧠.

💊 Treatment of IMPA

1. NSAIDs and Corticosteroids

While NSAIDs can help in mild cases, most dogs require corticosteroids (like prednisone) to suppress the immune attack 🧴.

• ❗ Never mix NSAIDs and steroids—this risks stomach ulcers
• 📉 Doses are tapered slowly once symptoms improve

2. Doxycycline Trial

If tick-borne diseases are suspected, your vet may try doxycycline. If your dog improves within 48 hours, infection was likely the trigger. If not, immune suppressants are used.

3. Immune-Suppressive Medications

If steroids alone aren’t enough, your vet may add one or more of these:

• 🧬 Cyclosporine
• 🧫 Azathioprine
• 🟣 Mycophenolate mofetil
• 🟠 Leflunomide

4. Supportive Care

• 🦴 Gabapentin for nerve-related pain
• 💊 Joint supplements (omega-3s, glucosamine)
• 🍲 Appetite stimulants or anti-nausea meds
• 💧 IV fluids or supportive therapies as needed
• 🏃‍♀️ Physical therapy or massage

Important: Never stop or alter meds without veterinary guidance. Flare-ups can occur if therapy is withdrawn too soon 🔁.

🔎 Monitoring and Long-Term Management

• 🔄 Periodic joint taps or imaging to track joint health
• 🧪 Regular blood tests to check for side effects
• 📋 Observation for flare-ups or medication responses

The goal is to use the lowest effective dose of the fewest drugs to control symptoms while preserving quality of life 🎯.

📈 Prognosis

Non-erosive IMPA: Fair to good prognosis with appropriate therapy. Some dogs improve and never relapse; others need lifelong medication 🔄.

Erosive IMPA: More guarded prognosis. Joint damage is progressive and may require surgery or ongoing therapy to manage comfort 🦿.

In both cases, early diagnosis and aggressive immune modulation offer the best outcomes 💪.

📲 Final Advice from Dr Duncan Houston

If your dog is showing signs of stiffness, swollen joints, or seems reluctant to walk, don’t delay. Early testing and treatment can improve outcomes dramatically 🐾.

For guidance on medications, supplements, and long-term monitoring, download the Ask A Vet App or visit AskAVet.com for expert veterinary support at your fingertips 💬📱.