Focal Inflammatory Myopathy in Cats
Myopathy is a general term that is used to denote any disorder of the muscles. Focal inflammatory myopathy is a localized form of the disease that affects specific muscle groups, in this case the masticatory (chewing) muscles and extraocular (eye) muscles.
The masticatory muscles are a group of four facial muscles that are used for chewing, and the extraocular muscles are a group of muscles, adjacent to eyeball, that control the movements of the eyes.
Focal inflammatory myopathy is suspected to be due to autoantibodies, or antibodies that are known to react against the body's own tissues. Antibodies are proteins found in the blood and which are used by the immune system to identify and destroy foreign invaders, such as bacteria and viruses. In effect, the antibody has crossed signals, mistakenly attacking the body as though reacting to a pathogen.
Focal inflammatory myopathy describes a condition in which these autoantibodies begin targeting the muscles of the affected animal. This disease is relatively rare in cats.
Symptoms and Types
- Problems with normal jaw movements
- Inability to get and keep food in the mouth
- Jaw pain
- Muscle swelling around jaw and face
- Progressive loss of muscle mass
- Swelling around eye
- Protrusion of the eyeball from the eye socket
You will need to give your veterinarian a thorough history of your cat’s health, including a background history of symptoms. After taking a detailed history, your veterinarian will conduct a complete physical examination on your cat.
Your veterinarian may attempt to manipulate your cat's jaw muscles to induce pain and swelling of the muscles so that the source of the problem is more evident. Your veterinarian will also try to open your cat's mouth, which often proves unsuccessful in these patients. Laboratory tests will include a complete blood count (CBC), biochemistry profile, and urinalysis.
The biochemistry profile may indicate higher levels of serum creatine kinase, indicating muscle injury. More specific testing includes taking a muscle tissue sample, especially important in masticatory diseases. This test can help in reaching a confirmatory diagnosis. More advanced testing may include demonstrating the autoantibodies against the muscle fibers. Diagnostic imaging will include X-ray of the jaw bones and ultrasound of the eye orbit to examine the swollen extraocular muscles. Magnetic resonance imaging may also be used to examine the muscle inflammation.