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Immune-Mediated Polyarthritis in Dogs

What Is Immune-Mediated Polyarthritis in Dogs?

Immune-mediated polyarthritis (IMPA) refers to a range of conditions in dogs where joint inflammation occurs due to the deposition of molecules by the immune system.

Typically, the immune system defends against external threats such as viruses and bacteria by producing protective antibodies that bind to and neutralize them, forming immune complexes. In IMPA cases in dogs, these immune complexes gather excessively in the joint fluid, drawing infection-fighting cells to inappropriate areas and resulting in harm to the smooth cartilage covering the joint bones.

Primary Immune-Mediated Polyarthritis in Dogs

The majority of immune-mediated polyarthritis (IMPA) cases in dogs are categorized as idiopathic, indicating that no clear cause for the immune response can be identified. This type is referred to as primary IMPA.

Secondary Immune-Mediated Polyarthritis in Dogs

Secondary immune-mediated polyarthritis (IMPA) in dogs occurs when immune complexes are formed due to infections, inflammation, or cancer elsewhere in the body. Distinguishing between primary and secondary IMPA is essential as addressing the underlying cause is vital for improving the dog’s condition.

Although IMPA is considered rare in dogs, its symptoms closely resemble those of other ailments, suggesting potential underdiagnosis and a higher prevalence.

IMPA can cause significant pain and impairment in dogs, necessitating prompt evaluation of clinical signs, preferably within days of onset. Dogs experiencing severe pain, fever, or loss of appetite may require emergency veterinary care.


  • Limping or lameness
  • Swelling and pain in the joints (typically affecting several joints)
  • Fever
  • Reduced appetite
  • Lethargy


The majority of primary cases of immune-mediated polyarthritis (IMPA) in dogs are considered idiopathic, meaning there is no known cause for the heightened immune response.

Certain breeds, such as Shar-Pei, Akitas, Duck Tolling Retrievers, and Greyhounds, may have genetic predispositions to IMPA, although any breed can be affected. Various factors can contribute to secondary IMPA in dogs, as any exaggerated immune response can result in the accumulation of immune complexes in the joints.

Inflammation or infection in the nervous system, heart, liver, and gastrointestinal tract are among the potential triggers. Tick-borne diseases like Lyme disease might also increase a dog’s susceptibility to IMPA. Less common causes include adverse reactions to medications and malignant tumors.


Diagnosing immune-mediated polyarthritis (IMPA) in dogs involves a series of tests to eliminate other conditions with similar symptoms.

Veterinarians typically begin with a comprehensive physical examination to identify areas of pain and inflammation in the dog. Suspicions for IMPA may heighten if the pain is sudden and affects multiple joints, particularly in breeds predisposed to the condition.

Diagnostic tests may include a complete blood count, blood chemistry, urinalysis, tick-borne disease screening, and chest and abdominal radiographs. These assessments help rule out alternative causes of joint discomfort and identify potential factors leading to secondary IMPA. If abdominal radiographs yield inconclusive results, veterinarians might recommend an abdominal ultrasound. Joint radiographs aid in ruling out fractures, ligament injuries, and bone cancer.

To rule out joint infection before initiating treatment for IMPA, an examination of the joint fluid is necessary. This involves arthrocentesis, a procedure that requires anesthesia and sterile preparation of the joint to prevent contamination. Analysis of inflammatory cell ratios and protein levels in the joint fluid can offer insights into the presence of IMPA.


Treatment for immune-mediated polyarthritis (IMPA) in dogs is feasible, with the prognosis heavily influenced by the type of IMPA suspected and whether it is primary or secondary. Swiftly controlling pain and inflammation before significant joint damage ensues can lead to a long and fulfilling life for your dog.

Treatment for Primary Immune-Mediated Polyarthritis in Dogs:

Primary IMPA is managed using medications that suppress the immune system, such as steroids or cyclosporine, to halt the deposition of immune complexes. In instances of severe joint damage, additional medications for pain relief and joint support may be necessary. While some dogs may be able to taper off medications after six to eight months, others might require lifelong therapy.

Treatment for Secondary Immune-Mediated Polyarthritis in Dogs:

Addressing the underlying cause of the immune reaction is imperative for managing secondary IMPA and preventing its recurrence. Depending on the situation, controlling the underlying condition may suffice, while in other cases, some level of immune system suppression may still be required. The diverse potential causes for similar clinical signs make IMPA one of the more challenging autoimmune syndromes to handle.

Living and Management

After initiating immune system suppression and effectively managing or resolving the underlying causes of immune-mediated polyarthritis (IMPA), dogs typically experience a swift clinical recovery, often feeling significantly better within days to weeks.

Once your dog has been free of symptoms for a minimum of two to four weeks, your veterinarian will typically attempt to taper down the doses of immunosuppressive medications.

The process of reducing medication doses can be gradual and may span several months, especially if multiple medications were necessary to control your dog’s symptoms. Some dogs may show signs of relapse at lower medication doses and may require higher doses for an extended period.

In severe cases of IMPA, long-term joint damage may occur, necessitating ongoing comfort management, as regrowth of joint cartilage is currently not possible. Maintaining your dog at a healthy weight is vital to minimize stress on damaged joints. Low-impact activities like swimming can help keep joints mobile and healthy without causing further injury.


Preventing primary immune-mediated polyarthritis (IMPA) in dogs can be challenging due to its unpredictable nature. However, you can reduce the risk of inflammatory conditions by ensuring your dog receives regular vaccinations and parasite prevention treatments.

Routine annual check-ups and screening blood tests can also aid both you and your veterinarian in detecting any underlying systemic diseases early, thereby potentially preventing the onset of an overactive immune system.

Immune-Mediated Polyarthritis in Dogs FAQs

What is the life expectancy of a dog with stage 4 arthritis?

Stage four arthritis, characterized by severe joint damage, can significantly affect your dog’s quality of life, prompting some pet owners to consider humane euthanasia.
The duration of a dog’s life with this condition largely depends on the management of pain. Pain control typically involves a combination of medications. Consult your veterinarian to explore medication and other pain management options.

Is immune-mediated polyarthritis (IMPA) in dogs genetic?

There is evidence indicating that certain genes may predispose some dogs to develop the excessive immune response associated with IMPA.

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