Immune-Mediated Inflammatory Reactions in the Joints of Dogs (Immune-Mediated Polyarthritis, IMPA)

  • Occurrence: very rare
  • Location of disease: General/Whole body, Legs
Author: Dr. med. vet. Gisa Löwe | Last modified: 14.08.2026
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Definition

Immune-mediated polyarthritis (IMPA) in dogs is an inflammatory disease in which the animal’s immune system attacks multiple joints, leading to Pain, Swelling, and restricted mobility.

The most important facts at a glance

Immune-mediated polyarthritis (IMPA) is an autoimmune disease in dogs where the immune system mistakenly attacks and inflames the joints. The exact cause is unclear, but genetic factors and certain dog breeds appear to be predisposed. IMPA can occur as primary, without other underlying conditions, or secondary due to infections, medications, or vaccination reactions. Hormonal and environmental influences like stress can also affect the disease.

Symptoms of IMPA include Fever, joint Swelling, Pain, stiff gait, and Lameness. Diagnosis is made through clinical examinations, blood tests, X-rays, and joint fluid analyses. These tests help rule out other causes and identify inflammation. Therapy aims to reduce Inflammatory conditions and relieve Pain. NSAID (non-steroidal anti-inflammatory drug)s and immunosuppressants like prednisone or azathioprine are commonly used. Complementary therapies such as physiotherapy and nutritional supplements can support recovery.

The prognosis depends on the severity of the disease and the response to therapy. Many dogs achieve a good quality of life, especially with early diagnosis. However, chronic problems and permanent joint damage are possible. Regular veterinary follow-up is crucial to monitor the course of the disease and adjust therapy. Since the cause of IMPA is not fully understood, there are no specific prevention measures. However, a balanced diet, regular examinations, and careful monitoring after vaccinations or medication administration can be helpful.

Causes

IMPA belongs to a group of autoimmune diseases in which the body’s immune system attacks its own cells or tissues. In IMPA, the joints are affected, leading to inflammation. The exact mechanism of why the immune system considers the joints foreign and attacks them is not yet fully understood. Scientists suspect that genetic predispositions play a role, as certain dog breeds are more frequently affected.

The disease can occur as primary, without other underlying conditions, or secondary in connection with other systemic diseases, infections, or as a reaction to medication. Secondary forms of IMPA can be triggered by infections such as Lyme disease or by vaccination reactions.

Hormonal and environmental influences can also play a role. For example, hormonal changes in unspayed female dogs can cause an exacerbation of symptoms. Environmental factors such as stress or other illnesses can increase the risk of developing IMPA.

Symptoms

Rare symptoms:

The symptoms of IMPA can vary from dog to dog, but typically include Lameness and Pain in multiple joints. This Lameness can migrate, meaning it can switch between different legs.

Affected dogs often show an aversion to exercise, are lethargic, and may show signs of Fever. The joints may be swollen and warm to the touch. In some cases, there may be general malaise and loss of appetite, indicating the systemic nature of the disease.

Additionally, joint noises or creaking may occur during movements, and in advanced cases, there may be a significant restriction of joint mobility, which greatly affects the dog’s everyday life.

Therapy

The therapy for IMPA aims to reduce inflammation and relieve Pain to improve the dog’s quality of life. NSAID (non-steroidal anti-inflammatory drug)s are often used to control Inflammatory conditions and Pain.

In many cases, however, immunomodulators or immunosuppressants are required to dampen the overactive immune response. Medications such as prednisone or azathioprine may be prescribed to suppress the immune system and control the inflammatory reaction.

Complementary therapies such as physiotherapy, acupuncture, or the use of nutritional supplements like omega-3 fatty acids can also be helpful in supporting joint health and further alleviating symptoms.

Prognosis and follow-up care

The prognosis for dogs with IMPA varies depending on the severity of the disease, response to therapy, and the presence of comorbidities. Many dogs respond well to therapy and can achieve a good quality of life, especially if the disease is diagnosed and treated early.

However, some dogs may develop chronic problems requiring long-term therapy. In rare cases, IMPA can lead to permanent joint damage, affecting the dog’s mobility.

Regular follow-up by the veterinarian is crucial to monitor the course of the disease and adjust the therapy as needed. Owners should be prepared that lifelong therapy may be necessary to prevent relapses.

Prevention

Since the exact cause of IMPA is not fully understood, there are no specific prevention measures for the disease. Nevertheless, some general measures can help reduce the risk.

A balanced diet and a healthy lifestyle can support the dog’s general health and strengthen the immune system. Regular veterinary examinations can help detect early signs of the disease and treat them promptly.

Since some medications or vaccinations are considered triggers for secondary forms of IMPA, they should only be administered after consultation with a veterinarian and when medically necessary. Careful monitoring after vaccinations or medication administration can help detect early signs of a reaction.

Outlook on current research

Immune-mediated polyarthritis (IMPA) in dogs is a sterile inflammation of multiple joints, meaning it is an arthritis without a detectable bacterial infection. Current research focuses primarily on two challenges: earlier diagnosis and better differentiation of subforms. Clinically, idiopathic (primary) forms and so-called reactive or secondary forms often appear very similar, even though they are likely biologically distinct. Arthrocentesis with synovial fluid analysis remains the diagnostic gold standard, and this is precisely where research is aiming to develop standardized criteria and supplementary markers. (pubmed.ncbi.nlm.nih.gov, merckvetmanual.com)

A second focus is the optimization of therapy. Glucocorticoids currently remain the most important treatment, but they are associated with relapses and side effects. Therefore, studies are investigating which other immunosuppressants are suitable as steroid-sparing strategies and which patients have a higher risk of recurrence. Simultaneously, there is interest in the role of triggering factors outside the joint, such as Inflammatory conditions in other organ systems. (pubmed.ncbi.nlm.nih.gov, merckvetmanual.com)

The overall outlook is positive but ongoing: research in the coming years is likely to provide more precise classification, individualized treatment, and better prognosis for the disease course rather than a single “miracle cure.”

Frequently Asked Questions (FAQs)

1. What is immune-mediated polyarthritis?
In immune-mediated polyarthritis (IMPA), the immune system mistakenly attacks the synovial membranes of multiple joints. This results in a non-infectious, sterile inflammation leading to Pain, Swelling, and Lameness. A distinction is made between non-erosive forms (the most common) and erosive forms, which can destroy cartilage tissue.
2. What are the possible causes?
A distinction is made between the idiopathic form with no identifiable cause (Type 1) and reactive forms associated with distant infections (Type 2), gastrointestinal diseases (Type 3), or Tumors (Type 4). Additionally, there are specific variants such as systemic lupus erythematosus and canine rheumatoid arthritis.
3. What symptoms do affected dogs show?
Typical symptoms include shifting Lameness in different limbs, a stiff gait especially after rising, Fever, lethargy, and loss of appetite. The joints are often warm and swollen, particularly the hock and carpal joints. Many dogs are initially presented for 'Fever of unknown origin'.
4. How is IMPA diagnosed?
The key diagnostic step is joint puncture / arthrocentesis of multiple joints. The synovial fluid shows a significant increase in neutrophils with a sterile culture. Additionally, a complete blood count, inflammatory parameters, autoantibody tests (ANA, rheumatoid factor), X-ray images, and a thorough search for underlying infections or Tumors are performed.
5. Which breeds are predisposed?
Any breed can be affected, but medium and large breeds such as the German Shepherd, Retriever, Doberman, Collie, and Akita are overrepresented. A specific variant is the juvenile polyarthritis syndrome in Akitas and Weimaraners.
6. How is IMPA treated?
The therapy of choice is immunosuppression with corticosteroids, usually prednisolone at an initially high dose. If there is an insufficient response or severe side effects, cyclosporine, leflunomide, mycophenolate, or azathioprine are also used. The dose is slowly reduced over several months.
7. How long does the therapy last?
Treatment usually lasts four to six months, often longer. Premature discontinuation of therapy frequently leads to a relapse. The reduction is carried out step-by-step, monitored by clinical examination, inflammatory markers, and, if necessary, a repeat joint puncture.
8. What is the prognosis for IMPA?
In the non-erosive idiopathic form, about 70 to 80 percent of dogs respond well to therapy, and some remain permanently free of recurrence. Reactive forms have a good prognosis if the underlying disease is treatable. Erosive forms, such as rheumatoid arthritis, follow a chronic progressive course.
9. Can relapses occur?
Yes, relapses are common, especially after a dose reduction that is too rapid. Regular check-ups are therefore important. Some dogs require long-term, low-dose immunosuppression.
10. How does IMPA differ from infectious arthritis?
In septic arthritis, usually only one joint is affected, and bacteria can be detected in the synovial fluid via culture. By definition, IMPA affects multiple joints simultaneously, and cultures remain sterile. An infection must be reliably ruled out before starting immunosuppression.

Literature

  • Cruzado Perez, J., Travail, V., Lamb, V., & Kelly, D. (2024). Canine immune-mediated polyarthritis: A review of 84 cases in the UK between 2011 and 2021. Veterinary Medicine and Science, 10(2), e1306. https://doi.org/10.1002/vms3.1306
  • Ravicini, S., Kent, A., Dunning, M., Baines, S., Clarke, S., & Allerton, F. (2022). Description and outcome of dogs with primary immune-mediated polyarthritis: 73 cases (2012–2017). Journal of Small Animal Practice. https://doi.org/10.1111/jsap.13565
  • Pichard, D., Robin, T., Le Boedec, K., & Benchekroun, G. (2025). Descriptive analysis and factors associated with relapse in dogs with presumptive idiopathic immune-mediated polyarthritis. Journal of Veterinary Internal Medicine, 39(5), e70241. https://doi.org/10.1111/jvim.70241
  • Wilson, R., Swift, I., Groth-Semple, M., Lee, S., Dann, T., Arafa, A., Poyton, C., & Thompson, M. (2024). Treatment with leflunomide in conjunction with glucocorticoids for dogs with immune-mediated polyarthritis is not associated with improved outcomes: A retrospective cohort study of 93 dogs from Australia (2017–2024). Veterinary Sciences, 11(11), 537. https://doi.org/10.3390/vetsci11110537
  • Chesne, R. B., Doornink, M. T., Sri-Jayantha, L. S. H., & Urie, B. K. (2024). Leflunomide with prednisone or nonsteroidal anti-inflammatory drug therapy is safe and tolerated for long-term treatment of immune-mediated polyarthritis in 27 dogs. Journal of the American Veterinary Medical Association, 262(9), 1188–1192. https://doi.org/10.2460/javma.24.01.0032
  • Rhoades, A. C., Vernau, W., Kass, P. H., Herrera, M. A., & Sykes, J. E. (2016). Comparison of the efficacy of prednisone and cyclosporine for treatment of dogs with primary immune-mediated polyarthritis. Journal of the American Veterinary Medical Association, 248(4), 395–404. https://doi.org/10.2460/javma.248.4.395
  • Shaughnessy, M. L., Sample, S. J., Abicht, C., Heaton, C., & Muir, P. (2016). Clinical features and pathological joint changes in dogs with erosive immune-mediated polyarthritis: 13 cases (2004–2012). Journal of the American Veterinary Medical Association, 249(10), 1156–1164. https://doi.org/10.2460/javma.249.10.1156
  • Rondeau, M. P., Walton, R. M., Bissett, S., Drobatz, K. J., & Washabau, R. J. (2005). Suppurative, nonseptic polyarthropathy in dogs. Journal of Veterinary Internal Medicine, 19(5), 654–662. https://doi.org/10.1111/j.1939-1676.2005.tb02743.x
  • Clements, D. N., Gear, R. N. A., Tattersall, J., Carmichael, S., & Bennett, D. (2004). Type I immune-mediated polyarthritis in dogs: 39 cases (1997–2002). Journal of the American Veterinary Medical Association, 224(8), 1323–1327. https://doi.org/10.2460/javma.2004.224.1323
  • Colopy, S. A., Baker, T. A., & Muir, P. (2010). Efficacy of leflunomide for treatment of immune-mediated polyarthritis in dogs: 14 cases (2006–2008). Journal of the American Veterinary Medical Association, 236(3), 312–318. https://doi.org/10.2460/javma.236.3.312