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Immune Mediated Polyarthritis (IMPA)

Lisa Allen

The most prevalent no identifiable cause diagnosed by exclusion-all other types have to be ruled out first. Young dogs of two to five years, particularly sporting breeds and large breeds are prone to cyclic fevers, stiffness and lameness typical of idiopathic polyarthritis. In some cases, neck pain is the only symptom that affected dogs exhibit.

Best managed with high doses of prednisone. Once a dog's clinical signs have resolved, his joint fluid should be re-evaluated to determine if the inflammation has truly dissipated. If it has, the Prednisone dosage can be safely decreased. But, about fifty percent of dogs with idiopathic polyarthritis require lifelong medication. UNIQUE FORMS OF POLYARTHRITIS HAVE BEEN DOCUMENTED IN ..., BERNESE MOUNTAIN DOGS,...tend to respond well to immunosuppressive therapy. Polyarthritis should aways be considered in a dog with lameness involving multiple joints and in one exhibiting vague signs of illness that could be related to joint inflammation…

Causes of polyarthritis:
bacterial
Borrelia (Lyme disease)
rickettsial
Ehrlichia
fungal
mycoplasma
IMMUNE MEDIATED
Non-erosive:
idiopathic (cause unknown)
systemic lupus-associated
reactive
breed-associated
Erosive:
rheumatoid
breed-associated (Greyhound)

How polyarthritis differs from degenerative joint disease...

DJD or osteoarthrosis is the most common type of joint disease in older dogs. They are not ill but the condition is painful. Degenerative changes are present in the joint cartilage but there is no inflammation of the synovium, the blood-vessel-lined membrane inside the joint capsule.

DJD develops as a complication of congenital defects such as ostoechondrosis dessicans and hip dysplasia; conformational defects; repetitive injury; and other forms of trauma. In most cases, only one or two joints are affected and the disease is slow to develop. Dogs with polyarthritis are often younger than those with DJD and they are commonly unwell (no appetite, fever) as well as lame. The disease comes on suddenly (good grief, does it ever! Moses was fine one day and quite ill the next day) but usually waxes and wanes. It may appear to respond to antibiotic or anti-inflammatory therapy only to recur at a later time. Many joints or just one can be affected during a polyarthritis flare.

DJD and polyarthritis tend to strike different joints; the larger joints, especially the shoulder, hip, and stifle, are prone to DJD whereas polyarthritis more commonly occurs in smaller joints like the carpus and hock (tarsus) as well as the elbow.

Non erosive polyarthritis and Lupus

Most common type of joint inflammation in the dog (non-erosive polyarthritis).

What occurs is that immune complexes, which are antibodies bound to foreign substances, settle in the lining of the joint (the synovium). These complexes initiate an inflammatory cascade by attracting inflammatory cells, which release inflammatory mediators (chemicals). Moses' polyarthritis was idiopathic immune-mediated non erosive polyarthritis.

When non-erosive polyarthritis is initiated by inflammatory and infective processes in other parts of the body, it is called "reactive." It has been reported in dogs with pyometra, inflammatory bowel disease, liver inflammation, mammary tumors, and even in dogs on drugs such as penicillin, trimethoprin-sulfa and phenobarbital. Effective treatment of the root problem usually resolves this type of secondary joint inflammation.

Another form of polyarthritis is Systemic Lupus Erythematosus (SLE). The body produces aberrant antibodies that react against joint tissue. This self-destructive process is not usually limited to joints as other cells and tissues can be targeted including the eyes, skin, nerves, kidneys, red blood cells and platelets. SLE is diagnosed with the aid of an antinuclear antibody test which detects the presence of aberrant antibodies. Dogs with SLE are given immunosuppressive drugs to curtail the inappropriate activity of their immune systems.

Types of polyarthritis

Infectious causes of polyarthritis are not common, as a group, in dogs. But you must check for them as there are treatments available which are effective. Once these are ruled out, immune-mediated processes must be considered. These diseases, which are of the erosive and non-erosive forms, are the most prevalent types of canine polyarthritis. Moses was diagnosed with non-erosive idiopathic immune mediated polyarthritis.

Rheumatoid arthritis, erosive, which causes pitting in the articular cartilage, can cause progressive joint destruction but is rare in dogs; when it does occur, it strikes, usually, middle aged or older Toy dogs. One looks for rheumatoid antibodies in the blood and biopsies the synovial membrane. Therapeutic management is achieved via immunosuppressive medication but resolution is difficult to achieve.

As I have mentioned before, there is some immune mediated disease on the side of Moses' sire.

Diagnosing polyarthritis

Many different infectious organisms can invade joints, so there are alot of specific tests available to diagnose them. (I think Moses had every test "in the book")!

A joint can become septic (invaded by bacteria) if a foreign body enters it, like a porcupine quill or during joint surgery or spread from the mouth as a result of severe dental disease, the heart (endocarditis, a heart valve infection), or the kidneys (pyelonephritis). Septic arthritis is diagnosed via a culture of joint fluid.

Lyme disease must be considered as a cause of arthritis; we tested Moses, with the help of veterinary schools in Oklahoma and North Carolina, for every tick disease known (just mostly involved serum samples).

To rule out the presence of a Mycoplasma organism in a canine joint, a joint fluid capsule must be cultured in specialized medium.

Establishing a diagnosis of polyarthritis

Establishing a diagnosis of polyarthritis is not easy. Indeed, it is not; other things must also be considered. It took several weeks and many tests to establish Moses' diagnosis; a joint tap ordered by Angell Memorial Animal Hospital's fine internal medicine (ACVIM) specialist, Dr. Maureen Carroll, in early June of 2001, confirmed such.

The first step is to take Xrays, which we did; Moses was "fine" by then, it seemed and the Xrays were unremarkable. Indeed, in most cases, the Xrays reveal bones that look normal, except in advanced disease. If arthritic changes are present, its more likely the dog has degenerative joint disease.

Then, fluid must be collected from several joints to be examined under a microscope. Joint inflammation is signalled by the presence of an increased number of white blood cells, specifically neutrophils. Inflammation can be triggered by infectious agents or immune disorders so more testing is needed.

Polyarthritis, and so it begins...

The very best article that i have ever read regarding polyarthritis is by Jeff Grognet, DVM B.Sc (Agr.) It is in the March 2004 "Dogs In Canada."

It describes an immune mediated imflammatory disease of multiple joints; some dogs with this, like Moses, might not even limp but just be depressed, without appetite and febrile; in May, 2001, Moses experienced some shoulder area pain that almost immediately resolved; several days later, I found him, suddenly, lying on his side in the yard and he could only move with great difficulty; we sought immediate veterinary care. This is a not uncommon presentation of polyarthritis. It might begin with a little stiffness but, then, it progresses. Eventually, affected joints will lose their range of motion, begin to grate with movement and then become unstable. Though the dog might limp on but one leg at a time, multiple joints in two or more legs are usually involved.

The very best article that i have ever read regarding polyarthritis is by Jeff Grognet, DVM B.Sc (Agr.) It is in the March 2004 "Dogs In Canada."

It describes an immune mediated imflammatory disease of multiple joints; some dogs with this, like Moses, might not even limp but just be depressed, without appetite and febrile; in May, 2001, Moses experienced some shoulder area pain that almost immediately resolved; several days later, I found him, suddenly, lying on his side in the yard and he could only move with great difficulty; we sought immediate veterinary care. This is a not uncommon presentation of polyarthritis. It might begin with a little stiffness but, then, it progresses.

Eventually, affected joints will lose their range of motion, begin to grate with movement and then become unstable. Though the dog might limp on but one leg at a time, multiple joints in two or more legs are usually involved.