To the best of my knowledge, I have only seen two cases of IMPA (immune-mediated Polyarthritis). The first case, I was the one that detected the abnormalities (switching and multiple joint swellings from treatment to treatment) and referred back to the DVM for further investigation. The second one was just recently, and of the two times I saw the dog, I missed it, but the neurologist determined that dog was too sore ‘everywhere’ on the day he saw him for it to be a pinched nerve. So the dog was referred to internal medicine who did the work up, and at the time of this writing, we are all still awaiting test results.
So, I figured it would be a good refresher topic for everyone to look at IMPA.
The exact CAUSE of immune-mediated polyarthritis (IMPA) in dogs is not fully understood, and it is considered an autoimmune disease. An autoimmune disease occurs when a dog's immune system, which is designed to protect the body from foreign invaders such as bacteria and viruses, mistakenly starts attacking the dog's own tissues and cells, in this case, the synovial membrane in the joints. While the precise triggers are not known, there are several factors that may contribute to the development of IMPA:
- Genetic Predisposition: Certain breeds, such as the Greyhound, Shetland Sheepdog, and Beagle, are more prone to autoimmune diseases, including IMPA. Genetic factors may play a role in a dog's susceptibility to these conditions.
- Environmental Factors: Environmental factors, such as infections, vaccinations, and exposure to certain toxins, are believed to influence the onset of autoimmune diseases in genetically susceptible dogs. Some researchers speculate that specific infections may trigger an immune response that leads to IMPA in predisposed individuals.
- Immune System Dysfunction: An underlying dysfunction within the immune system can lead to autoimmune diseases like IMPA. The immune system fails to recognize the body's own tissues as "self," leading to an attack on the synovial membrane in the joints.
- Stress and Hormonal Factors: Stress and hormonal changes, including fluctuations in sex hormones, may contribute to the development or exacerbation of autoimmune diseases. Additionally thyroid hormones or dysregulation of cortisol can be a trigger. These factors can affect the balance of the immune system.
- Unknown Triggers: In many cases, the exact trigger for IMPA remains unknown, and it can develop spontaneously without a clear external cause.
Canine IMPA can present with a range of clinical signs, and their severity can vary from dog to dog. Common clinical signs of IMPA include:
- Limping and Lameness: Dogs with IMPA often exhibit lameness and reluctance to bear weight on affected limbs.
- Swollen Joints: Affected joints may appear swollen and warm to the touch due to inflammation.
- Stiffness: Dogs may experience joint stiffness, particularly after periods of rest.
- Pain: Dogs may vocalize or exhibit signs of pain when their affected joints are touched or manipulated.
- Fever: In some cases, dogs with IMPA may run a fever, which is a systemic response to inflammation.
- Generalized Malaise: Dogs with IMPA may exhibit lethargy, reduced appetite, and a decreased interest in physical activity.
- Progressive Worsening: If left untreated, IMPA can lead to irreversible joint damage, affecting a dog's quality of life.
Diagnosing canine immune-mediated polyarthritis can be challenging, as it requires careful evaluation of clinical signs, various diagnostic tests, and ruling out other potential causes of joint inflammation. The following steps are typically involved in diagnosing IMPA:
- Clinical Assessment: The initial evaluation includes a thorough physical examination of the dog, including an assessment of joint pain, swelling, and mobility. Veterinarians will also inquire about the dog's medical history and any recent changes in behavior or health.
- Blood Tests: Routine blood work is essential in diagnosing IMPA. This includes a complete blood count (CBC) and serum biochemistry to assess for elevated white blood cell counts, elevated C-reactive proteins, elevated erythrocyte sedimentation rate, elevated fibrinogen, and other markers of inflammation.
- Joint Aspiration: Joint fluid analysis is a crucial diagnostic tool. A veterinarian will perform joint aspiration, extracting fluid from the affected joint to assess its characteristics. In IMPA, the joint fluid often shows an increase in white blood cells and evidence of other inflammatory markers.
- Imaging: Radiographs (X-rays) and advanced imaging techniques, such as ultrasound or MRI, may be used to evaluate the extent of joint damage and to rule out other joint disorders.
- Biopsy: In some cases, a synovial tissue biopsy may be necessary to confirm the diagnosis. This involves the removal of a small piece of synovial tissue for examination under a microscope.
The treatment of canine immune-mediated polyarthritis is multifaceted and aims to manage inflammation, alleviate pain, and improve the dog's overall quality of life. Here are some key components of treatment:
- Immunosuppressive Medications: The primary treatment for IMPA involves immunosuppressive drugs like corticosteroids (e.g., prednisone) or other immune-modulating drugs (e.g., cyclosporine). These medications help to suppress the overactive immune response causing joint inflammation.
- Pain Management: Non-steroidal anti-inflammatory drugs (NSAIDs) – if the dog is not on prednisone, and other pain medications (i.e. opioids, codeine, gabapentin, etc.) may be prescribed to relieve pain and discomfort in affected joints.
- Supportive Care: Rest and limited physical activity can help reduce stress on inflamed joints. Weight management is also essential, as excess weight can worsen joint problems.
- Monitoring: Frequent re-evaluation by a veterinarian is necessary to monitor the dog's progress, adjust medications as needed, and address any potential side effects.
- Dietary Modifications: Some dogs with IMPA may benefit from dietary changes or supplements that support joint health. (i.e. joint supplements, weight management, Omega Fatty Acids, antioxidants, avoidance of food allergens.)
- Physical Therapy: Physical rehabilitation and therapeutic exercises may aid in maintaining joint function and reducing stiffness.
- Long-Term Management: In some cases, dogs with IMPA may require lifelong medication and management to prevent relapses.
Because the specific cause can vary from one dog to another, research in this area is ongoing, and veterinarians focus on managing the condition rather than targeting its root cause. Canine immune-mediated polyarthritis is a challenging condition that demands early diagnosis and comprehensive treatment. The treatment plan may evolve over time, depending on the dog's response to medications and the progression of the disease. While less common than many orthopaedic disorders, IMPA is an important differential diagnosis to have at the back of your mind when treating dogs in Rehab Practice.