Erosive, Immune-Mediated Polyarthritis in Dogs
Erosive, immune-mediated polyarthritis is an immune-mediated inflammatory disease of the joints, in which the cartilage of the dog's joint (articular cartilage) is eroded away. In this disease, cell-mediated immunity is thought to attack articular cartilage. The suspected causes for this are T lymphocyte effector cells that carry out the attack response, and an abnormal antigenic response to the host antibody. That is, an immune response to a substance that stimulates production of antibodies, an antigen, which acts as a “trigger”. In effect, the body is fighting against itself.
Leukocyte cells (white blood cells), leukocyte enzymes (catalyzing reactions), cell-mediated immunity, immune complexes (an antibody bound to its triggering antigen), and autoallergic reactions are all directed against cartilage components. This leads to an inflammatory response by the tissue surrounding the cartilage, and complement protein activation in response to the immunity displaying cells.
Destructive enzymes, which are released from inflammatory cells, damage the articular cartilage, synoviocytes (cells which produce a lubricating fluid, called synovia, for the joints), and chondrocytes (cartilage cells), leading to erosive changes in the joints.
The disease described in this medical article can affect both dogs and cats. If you would like to learn more about how it affects cats, please visit this page in the PetMD health library.
Symptoms for dogs are often cyclic, coming and going at random intervals. These symptoms include:
- Stiffness in walk
- Decreased range of motion
- Cracking sounds from the joints
- Joint swelling and pain in one or more joints
- Joint instability, subluxation (partial dislocation of the joint), and luxation (complete dislocation of the joint)
The typical onset of immune-mediated erosive polyarthritis in dogs is from eight months to eight years of age. Young Greyhounds, between the ages of 3-30 months, are most susceptible to erosive polyarthritis of Greyhounds (EPG), a specific type of this disease. There is also idiopathic erosive polyarthritis (IEP), which can occur in any breed and is of unknown cause.
The suspected causes for this form of joint cartillage erosion are T lymphocyte effector cells that carry out the attack response, and an abnormal antigenic response to the host antibody. That is, an immune response to a substance that stimulates production of antibodies, an antigen, which acts as a “trigger.” In cases of IEP, the cause remains unknown.
You will need to give your veterinarian a thorough history of your dog's health leading up to the onset of symptoms. Your veterinarian will perform a thorough physical exam on your dog, taking note of signs of pain, decreased range of motion, and any lameness.
A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, a urinalysis, and an electrolyte panel. Joint fluid aspirate will be taken for lab analysis, and submitted for bacterial culture and sensitivity. A biopsy (tissue sample) of synovial tissue will also help to make a definitive diagnosis.
X-ray images can also be used as a diagnostic tool. If an erosive, immune-mediated polyarthritis condition is present, it will be visible on the radiograph image.