Polyarthritis in Dogs

The finding of swelling and pain involving one or more joints is called polyarthritis. In most cases, joint swelling and pain is an indicator of degenerative joint disease, such as arthritis or a cruciate ligament rupture in the knee. However, polyarthritis can also point to an underlying systemic illness, such as an immune-mediated disease or infection. This article reviews the systemic causes, diagnosis, and treatment of polyarthritis in dogs.

What are the signs of polyarthritis?

At home, you may find that your dog has one or more of the following clinical signs:

• Stiff stilted gait
• Lameness that shifts between legs
• Appearance that your dog is walking on egg shells
• Reluctance to walk, stand, or jump onto furniture or in the car
• Cry in pain or whimper when standing or walking
• Poor appetite and reduced water drinking, especially if they are unable to walk to the bowl

Often, your dog will develop these signs of polyarthritis suddenly. However in some cases the signs may be chronic (more than 3 weeks in duration).

If you notice these signs at home, you should schedule your dog for an examination by a veterinarian. On physical examination, your veterinarian may detect swollen and warm joints. In some cases, a dog with polyarthritis may have a fever and swollen lymph nodes as well. During the evaluation, it is important that you share the following information about your pet with your veterinarian:

• Any region or state that your dog has traveled
• Current medications including the use of a topical or oral flea and tick preventative
• Any known exposure to ticks or fleas
• When your dog last received a vaccination
• History of cancer

What are systemic causes of polyarthritis?

A systemic cause of polyarthritis is a disease that originates outside of the joint but causes joint inflammation. The main causes in dogs include immune-mediated polyarthritis, tick-borne infectious disease, or septic arthritis (i.e., bacterial infection within the joint).

• Immune-mediated polyarthritis is a disorder of the immune system. The immune system in a normal dog protects against infection by recognizing the infection as foreign and removing the infection. In dogs with immune-mediated polyarthritis, the immune system abnormally recognizes the cells in the joint as foreign and attacks these cells causing inflammation in the joint. Immune-mediated polyarthritis may be idiopathic (meaning no underlying cause is identified) or be secondary to an infectious disease, medication, or cancer. Immune-mediated polyarthritis most commonly affects the wrist or ankle joints. Occasionally, immune-mediated polyarthritis can cause destruction and erosion of the bones of the joint (called erosive polyarthritis).  In these cases, you will see changes to the bones of the joint on x-ray and potentially deformities to the joint.
• Lyme disease, Rocky Mountain spotted fever, anaplasmosis, and ehrlichiosis are infectious diseases (called tick-borne diseases) that are spread by ticks and cause polyarthritis. Each infectious disease is spread by the specific species of tick that live in specific geographic areas in the United States. This is why sharing your pet’s travel history is important as it helps your veterinarian decide on the likelihood of these diseases. Dogs may show other signs of illness in addition to polyarthritis including nose bleeds, bleeding from the mouth, and kidney failure.
• Septic polyarthritis is most often caused by bacteria in the blood stream lodging in the joint causing inflammation. This disease often affects the knee, elbow, shoulder, or hip joint. Endocarditis (or bacterial infection of the heart valves) is a life-threatening condition that can cause septic polyarthritis. Your veterinarian may hear a heart murmur on examination if endocarditis is the cause.

How is polyarthritis diagnosed?

Your veterinarian may be suspicious of a polyarthritis after an examination is performed. Based on the findings from the examination and the history of your pet, your veterinarian may perform the following tests to diagnose polyarthritis:

• Complete blood count, biochemistry panel, and urinalysis to evaluate the overall health of your pet and organ function
• Sedated joint “taps” to collect fluid from the joint
• Cytology and culture of the joint fluid
• X-rays of the affected joints
• Infectious disease testing
• Echocardiogram to evaluate the heart valves
• Blood culture to identify bacteria in the blood

A joint “tap” is the best method to determine the diagnosis of polyarthritis. In all cases, dogs are sedated or anesthetized to provide them comfort during this simple procedure. After a sterile preparation of the dog’s skin around the joint, the veterinarian will insert a small needle into the joint capsule and use a syringe to collect joint fluid. The joint fluid is then placed on a microscope slide and the slide is evaluated under the microscope for inflammatory cells or bacteria. The joint fluid may also be submitted for a bacterial culture since bacteria are difficult to find with a microscope. Polyarthritis is diagnosed after inflammation is confirmed in one or more joints. In most cases, the procedure is well tolerated. Rarely, the pet’s clinical signs may worsen slightly from local inflammation or bleeding that can occur during the procedure.

What is the treatment for polyarthritis?

The treatment of polyarthritis depends on the underlying cause. For immune-mediated disease, your pet will be placed on one or more medications to suppress the immune system from attacking the joints. A common medication prescribed is the steroid prednisone. Dogs with immune-mediated polyarthritis may also require an antibiotic for the treatment of an infection or require treatment of a cancer present. Dogs with non-erosive immune-mediated polyarthritis often respond favorably to prednisone treatment within 7-14 days, or sooner. If your dog has erosive polyarthritis, the changes to the bone and deformities are often permanent.

Dogs with tick-borne disease will be treated with an antibiotic called doxycycline or related antibiotic. Dogs often show a favorable response to doxycycline within 3-5 days.

Dogs with septic arthritis are treated with a broad-spectrum antibiotic and hospitalization is often required. Antibiotic therapy is guided by the results of the joint and blood cultures. Dogs often require weeks to months of antibiotic therapy. Some dogs may require surgery to flush the joint.

What is the prognosis for polyarthritis?

Prognosis for immune-mediated polyarthritis depends on the response to treatment but in many cases the prognosis is good. Dogs often needs months of medications which are gradually tapered. The disease may relapse once the medication(s) are discontinued. In relapsing cases, the dog may require life-long medications to control the disease.

Dogs with tick-borne disease have a great prognosis. In rare instances, dogs with Lyme disease can develop an inflammatory kidney disease, called nephritis, which is poorly responsive to therapy.

Dogs with septic arthritis are often very ill and require hospitalization. In some cases, the condition is life-threatening and can cause organ failure. If caught early, dogs can respond favorable to antibiotic therapy and make a full recovery.