Myasthenia Gravis in Cats

Myasthenia gravis is either present at birth (congenital) or acquired (develops later in life). Most cats with acquired MG develop symptoms later in life, whereas kittens with congenital MG have symptoms immediately after birth.

Acquired MG has several forms depending on the severity and location. These forms include:

• Focal: Only one area of the body is affected, typically the esophagus and throat
• Generalized: All muscles are affected
• Acute fulminating: A rapidly progressive form of the disease that usually results in death due to paralysis of the respiratory muscles

Myasthenia gravis is a very rare condition in cats, but is potentially life-threatening.Cats showing symptoms of weakness, regurgitation, and vocal changes require prompt veterinary care to identify the underlying cause. Cats that regurgitate are at risk of developing aspiration pneumonia, where food material enters the lungs, which has a poor prognosis.

The severity of symptoms depends on the type of MG, with acute fulminating MG having the most severe and rapidly progressing symptoms.

Some cat breeds are predisposed to MG, including Devon Rex and Sphynx cats.

Myasthenia gravis is a condition where signals from the nerves to the muscles are disrupted, due to abnormalities in muscle receptors that respond to nerve signaling. Dysfunction of the muscle receptors prevents normal muscle contraction.

Acquired MG is most often an auto-immune disease, where the immune system damages signal receptors in the muscles. The reasons for developing this condition are unknown. In some cases, the immune system produces an abnormal reaction to certain drugs. Tumors affecting the thymus (an organ of the immune system), called thymomas, can also lead to acquired MG.

Note: Regurgitation is a common symptom of MG, due to the esophagus requiring muscle contraction to push food down into the stomach. In MG, the muscles cannot contract, and food within the esophagus migrates up into the mouth. Regurgitation is distinguished from vomiting by having no abdominal effort or retching; cats simply deposit food onto the ground with no obvious distress or effort.

To confirm a diagnosis of MG, a physical examination is performed. Other diagnostic tests include:

• Blood work
• Diagnostic imaging
• Administration of edrophonium chloride, a drug strengthens the signal from the brain to the muscle
• Electromyography
• Genetic testing for Sphynx and Devon Rex cats

Once a diagnosis is confirmed, treatment involves a combination of medication and life-long management.

Treatment includes:

• Medications that increase the strength of signaling from the brain to the muscles
• Immunosuppressive medications to reduce destruction of signal receptors
• Nutritional management in cats with megaesophagus, including feeding soft, high-calorie feed and elevating the food and water bowls

Cats with MG must be closely monitored for any signs of aspiration pneumonia, such as difficulty breathing or rapid breathing.

Myasthenia gravis is a life-long condition, and management can be difficult in cats. Many cats are euthanized due to the need for ongoing management and risk of severe complications.

Cats that are successfully managed often enter periods of remission where treatment is no longer required for a length of time. MG associated with thymomas, congenital MG, and the acute fulminating form also have a poor prognosis.

There is no guaranteed method for preventing acquired myasthenia gravis. Cat breeds that are known to have congenital MG as a genetic disease can be carefully selected to avoid pairing carriers of the disease. Myasthenia gravis is not contagious.

Myasthenia gravis is very rare in cats.

• Medications to enhance signaling from brain to muscles
• Immunosuppressive medications
• Nutritional management