Immune-Mediated Poly-Arthritis in Dogs

This type of arthritis is similar to rheumatoid arthritis that impacts humans as well. There is often times no cause or reason behind the arthritis and the symptoms can come and go without explanation. There is no cure for arthritis, however, there are ways to help your dog live his best and most comfortable life.

This disorder is the most common type of arthritis for dogs and can cause pain, difficulty walking, muscle atrophy, and more in your dog. This condition can cause symptoms that mimic other disorders as well and there is no guarantee that your dog will exhibit textbook symptoms. Immune-mediated poly-arthritis can impact both small and large breed dogs equally.

Immune-mediated poly-arthritis (IMPA) is a noninfectious disorder of your dog’s immune system that impacts his joints. It is possible to cause inflammation in all joints which can cause your dog to be in discomfort and pain.

The symptoms of IMPA can vary and look like other disorders, as the signs are often generic to multiple disorders. The symptoms listed may not all be present and may come and go over time.  

• Lameness
• Multiple joint pain
• Joint swelling
• Fever
• Malaise
• Anorexia
• Lethargy
• Difficult walking/standing
• Stiffness
• Vomiting
• Diarrhea
• Lymph nodes enlarged

Types

There are 2 larger subtypes – erosive and nonerosive IMPA and within that there are 4 subtypes of IMPA – Type I, Type II, Type III and Type IV. Erosive IMPA indicates there has been some damage to bone and/or cartilage. Nonerosive indicates there has not been any damage to bone or cartilage in your dog. 

Type I – Non identifiable disease

• Most common of all IMPA
• Accounts for more than 50% of all cases of IMPA in dogs
• Diagnosis of exclusion

Type II – Infectious or inflammatory disease related

• Superficial pyoderma
• Urinary tract infection
• Pneumonia
• Endocarditis
• Mastitis
• Dirofilariasis
• Fungal infection
• Pleuritis
• Severe periodontal disease
• Diskospondylitis
• Chronic salmonellosis
• Bacterial prostatitis
• Bacterial tonsillitis
• Pharyngitis
• Dermatitis
• Pancreatitis

Type III – Seen with chronic stomach disease

• Inflammatory bowel disease
• Intestinal malabsorption
• Bacterial overgrowth
• Ulcerative colitis
• Chronic and bacterial diarrhea
• Eosinophilic gastric
• Lymphocytic-plasmacytic hepatitis

Type IV – Associated with abnormal cells

• Squamous cell carcinoma
• Mammary adenocarcinoma
• Leiomyoma
• Heart base tumor
• Seminoma

Other types

• Breed associated
• Drug associated
• Vaccine associated

In the subtypes I-IV, 3 of them have known causes and those cases make up about 50% of dogs diagnosed with IMPA. However, Type I does not have any specific known causes and accounts for 50% of cases. 

Type I 

• Typically, no known cause
• Common in all ages and breeds

Type II

• Reactive to an infection
• Bacterial infection
• Fungal infection
• Viral infection

Type III

• Stomach/intestinal related
• Liver related
• Rare in dogs

Type IV

• Overgrowth of cells outside of your dog’s joints
• Rarest form of IMPA 

Other Causes 

• Breed associated (Akita, Chinese Shar-Pei, Boxer, Weimaraner, Bernese Mountain,German Shorthaired Pointer, Spaniel and Beagle breeds)
• Drug associated (given within 30 days of onset of symptoms, but typically occurs within 5-20 days after drug administered - sulfonamides, lincomycin, erythromycin, cephalosporins, phenobarbital, penicillins)
• Vaccine associated (administered within 30 days of onset of symptoms, somewhat weak link between the 2)

If you begin to notice that your dog is suffering from pain, discomfort, difficulty walking and other odd symptoms with no readily available explanation, your veterinarian may be able to help you. Your veterinarian will most likely want to do a full physical exam on your dog to see if he is having pain, swelling in his joints, unexplained fever and other common symptoms to begin diagnosing.

Once your veterinarian performs a physical exam she will most likely want to hear about your dog’s history of other health concerns including any medication changes or recent vaccinations, injuries, exposure to anything that could have resulted in his symptoms. While a physical exam and history alone can diagnosis IMPA, your veterinarian may want to run some tests as well.

These tests could include drawing fluid from your dog’s joints (arthrocentesis), and x-rays of joints he is feeling pain in to see any deterioration of those areas. Your doctor may want to rule out lyme disease, other tick borne disease, and any other possible underlying causes via blood tests. Tests may be done on your dog’s stomach to determine if the cause is Type III as well – including ultrasounds, x-rays or scans. 

When prepping for your visit with your veterinarian it is important to gather as much information as possible to share with her about your dog. It would be beneficial to have a timeline of how long your dog has been suffering from symptoms and what his exact symptoms are. It would also help your veterinarian to make the best diagnosis for your dog if you can give any specifics as to when it gets worse or better, or if you have noticed the symptoms come and go over time, as arthritis symptoms tend to do this.

In terms of treatment options for your dog, your veterinarian will most likely suggest medication management for your dog’s symptoms as the disease is not curable. Learning to manage your dog’s symptoms will lead to a happier, healthier and pain-free life for him. 

Medication management for your dog’s symptoms is the go to option for many veterinarians. These medications fall under two categories which are immunosuppressive  and chemotherapeutic medications. Immunosuppression medications will be anti-inflammatory typically, such as corticosteroids (prednisone) alongside other medications (chemotherapeutic) such as Azathioprine, Leflunomide, and Cyclophosphamide. Long term corticosteroid use can have side effects also such as diabetes, urinary tract infections and hyperadrenocorticism. 

It is recommended that liver enzymes be checked out if your dog is on Azathioprine, and side effects can include bone marrow becoming suppressed and cystitis. Azathioprine can be used for a longer period of time than Cyclophosphamide which is not recommended past four months of use. 

Immunomodulation drugs which are used to regulate your dog’s immune system have been found to be beneficial if your dog’s IMPA does not go in remission or they have a relapse of symptoms. There are some side effects however, such as lethargy, vomiting, diarrhea, agitation, and anemia. 

Medication management is done over the course of 2-4 months and if your dog is responding, your veterinarian will begin to taper him down off of the medications. The taper can take another 2-4 months after that. 

There is a high rate of relapse with IMPA due to the fact that it can act up anytime and without warning. The prognosis is good for Type I with ongoing medication management. Types II-IV have a good prognosis assuming the underlying cause of their IMPA is treated adequately in order to take care of the IMPA symptoms. Up to 56% of dogs have gotten off of medication management therapy.

It will be important as your dog continues to age and grow to have him checked out regularly for any changes in his IMPA symptoms and any necessary medication changes. Your dog may relapse as discussed above, so follow up appointments will be beneficial to keep him comfortable. 

If it has been found that your dog’s IMPA was the cause of Type II-IV you may have to continue working with his veterinarian to ensure those underlying issues are continuing to be taken care of as well. Keeping up with your dog’s medication and making sure he is taking them as directed will also help him to remain pain-free.

Lastly, as there is no cure for IMPA you can expect to deal with possible flare ups throughout your dog’s life. However, once the underlying issues are handles in Types II-IV it should be easier to control the IMPA and your dog should be able to continue his normal routine.