Immune-Mediated Arthritis

Your pet has been diagnosed with immune-mediated arthritis. Symptoms topically include reluctance to walk or move and/or painful, swollen joints. There are two broad types of this condition, one caused by infection in the body (less common) and one caused by "autoimmunity" (more common). Both cause fever and both appear similar to the pet owner and to the veterinarian. It is important to differentiate between the two types of disease because the treatment for one is in direct opposition to that for the other. When immune-mediated arthritis is caused by infection in the body, the infection is usually not in the joints themselves. Rather, the infection is often deep seated in the body, for example, in the uterus or prostate, on a heart valve, in a kidney, on the spine, or elsewhere. The infection may also be body wide, such as those that result from the bite of a tick, such as Lyme disease, or those caused by internal fungal infections. Minor or superficial infections in the body do not usually cause this disease. The presence of inflamed joints resulting from an infection elsewhere in the body is similar to the human condition of "achy joints" in the presence of influenza (a human lung infection). In this instance, the infectious virus itself attacks the lungs, yet the body's immune system that fights off the infection attacks the joints as "innocent bystanders," making them sore and inflames. Typical tests to find the source of internal infection would include a thorough physical examination, routine screening of blood and urine samples, and a bacterial culture of the urine. More advanced testing may be indicated depending on the specific case and your geographic area and may include radiographs (x-rays) or ultrasound examination of the body, serologic (blood) tests for the presence of an infectious disease, and/or a bacterial culture of the blood or spinal fluid. In all cases, an analysis of the fluid that bathes the joints (synovial fluid) is necessary to make the diagnosis of immune-mediated arthritis (either type). A small needle placed into the joint after the pet has been given a light sedative is all that is needed to collect a sample. Analysis of this fluid can aid the veterinarian in determining whether an infectious or autoimmune condition exists. Usually, however, the diagnosis is made by reviewing all test results and relating them to the patient's history and physical examination findings. When the infection in the body (if present) resolves, either through antibiotic treatment by the veterinarian or spontaneously, the inflammation in the joints (arthritis) almost always resolves permanently as well. If a thorough examination and testing have not identified a source of infection in the body, the condition is termed "autoimmune" arthritis. An autoimmune disease is one in which the body's immune system (the circulating white blood cells and molecules that fight infection) has malfunctioned. Instead of performing its intended job, the immune system has been misdirected and has begun attacking parts of the body itself. In autoimmune arthritis the attack occurs at the lining of the joints. The reason for this misdirected attack is not clear but could be related in some way to the animal's genetic makeup. Certain breeds of dogs are prone to this condition, and there is an age group and gender association. A typical dog with this disease is a 2- to 6-years- old large, female "sporting" breed dog. However, almost any age, breed, or sex of dog or cat may develop this disease. A particularly debilitating form of this disease, rheumatoid arthritis, typically affects aging, smaller to toy breeds of dogs. Autoimmune arthritis may occur by itself or may be part of an attack on several areas of the body, such as part of an attack on several areas of the body, such as systemic lupus. Lupus is a generalized autoimmune disease in which the immune system attacks not only the joints but also the skin, kidneys, nervous system, blood cells, or other organs. The cause of lupus is not known but is presumed to be at least partially genetic. Treatment for this form of the disease involves "turning off" or suppressing the immune system, thereby alleviating the inflammation in the joints. The drug most commonly used for this purpose is prednisone (cortisone). Prednisone itself is usually enough to treat the disease effectively. Common side effects of prednisone include increased water drinking, increased urination, increased appetite, weight gain, and panting. These effects are bothersome but not serious and should dissipate when the dose of the medication is decreased. Sometimes more potent immunosuppressive drugs need to be added to the protocol. In this case, care must be taken to avoid too much weakening of the immune system. This requires careful monitoring and regular blood checks by the veterinarian. In approximately 50 per cent of animal treated, the medication is eventually withdrawn over a period of many weeks to months and the prognosis is excellent. The remainder of affected animals has relapses with symptoms during gradual withdrawal of medication. Most of these relapsing cases are managed effectively with some tolerable dosage of medicine that needs to be continued for the long term or indefinitely. The goal of therapy in chronic or relapsing cases is to administer the minimum effective dose to control symptoms. This minimized some potentially troubling side effects of the medication. The above is general veterinary information. Do not begin any course of treatment without consulting your regular veterinarian. All animals should be examined at least once every 12 months.