Arthritis is a general term for inflammation and pain of the joints. It is a common condition affecting both people and animals and comes in different forms. In dogs, the most common type of arthritis is osteoarthritis (OA), this means pain and inflammation of the joint due to wear and tear. Dogs with predisposing factors are at higher risk of developing this disease, such as hip and elbow dysplasia. Generally, this type of arthritis is slow onset. However, it’s not the only cause. Looking at causes of sudden onset arthritis gives a different range of disease processes that we need to consider.
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Other types of arthritis
Septic arthritis
Septic arthritis or “septic joint” means a joint in the body, usually a large joint such as the tarsus (hock joint) or carpus (wrist joint), has become infected. This results in heat, pain and swelling, meaning the dog becomes suddenly lame and painful. This infection can be a result of a penetrating wound around the joint. This means bacteria has got into the joint, or a systemic disease meaning bacteria has got into the joint via infected blood.
It often affects only one joint and is diagnosed from radiography and taking a sample of joint fluid. This joint fluid sample will show an elevated level of white blood cells and proteins in the case of a septic joint; these samples can also be cultured which can help show which bacteria are causing the problem. Treatment includes pain relief and antibiotics. It may require hospitalisation depending on how poorly the dog is and how well their pain is controlled.
Immune mediated polyarthritis (IMP)
This type of arthritis is not caused by degeneration of the joint, as with OA, or infection, like in septic arthritis, but is caused by an immune system overreaction. This results in the body’s own immune system attacking and damaging the joint.
What does IMP look like?
In dogs, IMP presents as a dog of varying age or breed with multiple joints affected. This can look like a shifting lameness, or one joint may be affected then improve, then a different joint become affected in the same way a few days later. They can sometimes be unwell in themselves, with non-specific signs such as inappetence, fever and lethargy.
What causes IMP?
IMP can be sub-categorised based on the inciting cause. These conditions are largely grouped into idiopathic (meaning unknown cause), secondary to a non-joint infection, secondary to a gastrointestinal disease or secondary to a cancer. As IMP is caused by an immune overreaction, dogs can, rarely, have this secondary to a vaccination.
How is IMP diagnosed?
In the same way as septic arthritis is diagnosed, cases of IMP will need radiography of the affected joints, as well as joint fluid samples taken and analysed. With IMP, it is particularly important that multiple samples are taken from different joints, as the diagnostic feature of this disease is the involvement of multiple joints. To investigate the underlying cause of IMP, your vet may want to rule out infection, including blood panels for vector-borne diseases such as Lyme disease, as well as considering further imaging to investigate presence of cancers. If the underlying cause of IMP can be found and treated, the IMP should also resolve.
How is IMP treated?
The primary treatment for IMP is an immunosuppressive dose of steroids, this dampens down the overactivity of the immune system to stop the attack on the joints. This treatment will be needed at a high dose, at least for the initial part of the treatment course, and you may see side effects such as weight gain, panting and increased urinating and drinking.
It is important that this medicine isn’t stopped suddenly however, and often requires slow reduction of the dose over many months. Some animals require multiple types of immunosuppressive drugs. Depending on the inciting cause for the IMP, further treatment may be needed, for example, if a vector-borne disease is suspected, a course of antibiotics may be needed. Symptomatic care will also be required, such as pain relief.
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