My veterinarian said my dog has polyarthritis. The dog has been ill for several months and has been hospitalized several times for swelling of the hocks and elbows. He has received intravenous antibiotics in the hospital and then oral antibiotics after discharge. He does a lot better on the IV drugs and seems to relapse while on the oral medications. What causes this?
You have described a joint disorder in which multiple joints are diseased. If six or more of the joints are inflamed and contain white blood cells, then the condition is termed polyarthritis. Polyarthritis may be erosive or non-erosive. In the erosive form, the underlying disease process erodes the cartilage; in the non-erosive type, the cartilage is not affected. The polyarthritic conditions discussed here are immune-mediated; the affected animal's immune system reacts to an antigen (immune stimulus) in or about the joints. The result may be painful joints, lameness or stiff gait, loss of appetite, fever, diarrhea, and sometimes excessive thirst and urination. Polyarthritis is different than non-immune-mediated arthropathies such as osteoarthritis ("wear and tear arthritis") or degenerative joint disease.
There are numerous causes of polyarthritis, including systemic lupus erythematosus (SLE), polyarteritis nodosa and other collagen-vascular diseases and infectious diseases involving Lyme bacteria, Ehrlichia species or other rickettsial organisms. Cancer and inflammatory bowel disorders may also trigger polyarthritis. These causes provoke an inflammatory reaction that does not result in erosion of the affected joints. Rheumatoid arthritis, in contrast, causes erosive changes in the joints, where inflammatory products erode or "melt" the cartilage within the joints; often the joints collapse after chronic inflammation.
Diagnosis of polyarthritis is based on patient history, physical examination, laboratory tests and radiographs (x-rays). Laboratory tests may include a complete blood count, chemistry panel, and urinalysis. Tests for SLE and infectious diseases may be needed. Laboratory analysis and bacterial culture of joint fluid samples provide critical diagnostic information, as well.
In most dog patients, however, the cause of polyarthritis is never identified and is referred to as idiopathic. Affected patients must have all possible known causes ruled out before a diagnosis of idiopathic polyarthritis is made. Along with the known causes, idiopathic polyarthritis is assumed to be an immune-mediated phenomenon and is treated the same as the known, noninfectious causes of polyarthritis.
Patients with polyarthritis are offered rest. Polyarthritis is treated with immunosuppressive doses of corticosteroids, especially prednisone. Additionally, certain cytotoxic drugs may be used along with corticosteroid agents. Antibiotics and other drugs to treat underlying infections, when present, and other causative diseases may be appropriate. Nonsteroidal anti-inflammatory drugs are less useful, but may be used while awaiting test results or if transient or mild disease is suspected.
If the underlying cause is an infection, clearing up the infection before using immunosuppressive drugs is essential. (Steroids can cause infections to spread.) Often the idiopathic conditions wax and wane, and may appear to be more influenced by beginning and discontinuing antibiotics (if antibiotics are not given continuously). Hidden bacterial infection that seeds the joints may require weeks of continuous treatment. If the signs of polyarthritis recur during treatment, then a sterile or idiopathic polyarthritis may be more likely than one associated with infection. Additionally, at the present time, the possibility that a particular type of antibiotic might also trigger the immune reaction leading to polyarthritis cannot be excluded.
Surgery to fuse the joints may be needed in cases of debilitating, erosive polyarthritis, concurrent with treatment of the inflammatory disease process.
05/07/01
