Immune-Mediated Polyarthritis (IMPA)

Immune-Mediated Polyarthritis (IMPA) is an autoimmune disease causing inflammation and pain in multiple joints, primarily affecting young medium to large breed dogs. It can be diagnosed through joint fluid analysis and treated with immunosuppressive medications, such as prednisone.

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Summary

IMPA is a condition where the immune system attacks the dog’s joints, causing pain and lameness. Diagnosis involves analysing joint fluid, while treatment typically includes immunosuppressive medications like prednisone. Most dogs respond well to treatment, but some may need long-term medication or experience relapses.

Immune-Mediated Polyarthritis (IMPA) is an autoimmune disease that causes inflammation and pain in multiple joints due to an abnormal immune response. It primarily affects young medium to large breed dogs and is rarely seen in cats. Dogs can develop either primary IMPA, which occurs without an underlying condition, or secondary IMPA, which happens due to another disease or certain medications. Conditions associated with IMPA include cancer, infections, and intestinal inflammation.

Arc Sheltie Dog Breed Lying On Grey Couch Seat

What are the Signs of IMPA?

Dogs with IMPA often present with sudden stiffness and shifting lameness, where they may limp on one leg one day and another the next. They may also exhibit fever, pain, lethargy, and decreased appetite. In severe cases, dogs may be unwilling to walk or stand, which can be confused with neurological disorders. Dogs with secondary IMPA may show additional signs related to the underlying condition.

How is IMPA Diagnosed?

To diagnose IMPA, a veterinarian collects joint fluid samples from multiple joints while the dog is sedated. This procedure is minimally invasive and not painful during recovery. The samples are sent to a lab for analysis, including bacterial culture and cytology. If inflammation is detected in multiple joints, it suggests the presence of IMPA. Further tests such as chest X-rays and abdominal ultrasound may be conducted to determine any underlying causes.

Various pictures showing veterinary procedure performed on a dog
Joint fluid collection in dog with suspected IMPA. The dog was sedated so these procedures did not cause any discomfort.

What is the Treatment for IMPA?

Dogs with primary IMPA are treated with immunosuppressive medications, most commonly prednisone. This steroid is generally well-tolerated but may increase appetite, thirst, urination, and panting, as well as predispose the dog to secondary infections. Most dogs respond quickly to prednisone and often return to normal within a few days. The medication is gradually reduced over a period of 4-6 months.

If secondary IMPA is diagnosed, treatment involves addressing the underlying cause and possibly starting immunosuppressive medications.

What is the Prognosis for Dogs with IMPA?

Around 90% of dogs with primary IMPA respond well to immunosuppressive treatment. A complete cure is reported in 56% of dogs, while 18% may need lifelong medication. Relapse occurs in 20-48% of dogs. The prognosis for secondary IMPA depends on the underlying cause; if the cause is not resolved, IMPA may persist.

The internal medicine team at ARC is dedicated to helping dogs with IMPA recover and enjoy their best lives.