Myasthenia Gravis in Dogs and Cats

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Myasthenia Gravis in Dogs and Cats

Myasthenia Gravis (MG) is a disease that causes severe muscle weakness and can look like your pet is becoming paralyzed. It is not a common disease and is seen more often in dogs than cats. Keep reading to learn about the symptoms, causes, and treatments for myasthenia gravis in dogs and cats.

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While rare, puppies and kittens can be born with an inherited or congenital form of MG. Predisposed breeds include Jack Russell Terriers, English Springer Spaniels, Smooth Fox Terriers, and Smooth-Haired Miniature Dachshunds.

Acquired MG is seen more often vs. inherited, and owners may notice signs in dogs between 1-4 years of age or 9-13 years of age. Breeds at risk for acquired MG include Newfoundlands, Great Danes, Golden Retrievers, Labrador Retrievers, Akitas, and Scottish Terriers.

What causes Myasthenia Gravis (MG)?

In most animals, MG develops when the immune system (the system which normally fights off disease or infection) mistakenly does not recognize the body’s normal muscle tissue as its own and attacks it. The “attack” happens at the microscopic cellular level, affecting the animal’s muscles and causing weakness.

Puppies and kittens with MG at birth, are born with abnormal muscle tissue rather than an immune problem. Few can outgrow the disease, however, and most have a shorter than normal lifespan.

In some cases, dogs and cats with other diseases such as certain kinds of cancer, hypothyroid disease, thymus problems, and other illnesses, have an increased possibility of developing MG.

Symptoms of Myasthenia Gravis in Dogs and Cats

In most cases, the following symptoms are seen and worsen over a period of days to months. Rarely, symptoms can develop suddenly, and the dog or cat may not be able to stand.

  • Weakness of all 4 legs, especially after exercise. Owners often report that their dog wants to continue to run and play but simply doesn’t have the energy or strength.
  • Passive regurgitation of food, often mistaken for vomiting. Dogs will regurgitate food from their stomach without the heaving that is seen with vomiting.
  • Muscle tremors
  • Increased salivation (excess)
  • Voice changes
  • Eyes have dilated pupils
  • Unable to close the eyes even when sleeping
  • Coughing or difficulty breathing

A form of acquired MG involves the muscles of the esophagus (which is the tube that carries food from the mouth to the stomach) called megaesophagus. Megaesophagus is a dilation or widening of the esophagus and dogs will often have their food return up through their mouths without the signs normally seen with vomiting (also known as regurgitation). Dogs may have difficulty swallowing, may be less able to blink, and may collapse suddenly.

Diagnosing Myasthenia Gravis in Dogs and Cats

If, after getting a thorough history from the owner and performing a physical exam, a vet suspects MG, several tests are recommended which help determine the diagnosis. This includes several blood tests, urinalysis, chest x-rays, electrocardiogram (ECG), and cardiac ultrasound (echocardiogram).

The best way to diagnose MG is for your vet to submit a blood sample for a particular test, to a special laboratory. Test results can take several days and a positive result along with the symptoms described above confirms the diagnosis of MG.

Living with the Diagnosis of Myasthenia Gravis

Pets diagnosed with MG need ongoing veterinary monitoring and treatment management. It can take several adjustments to the medication(s) to find the best combination that works for each patient.

Dogs and cats diagnosed with megaesophagus as part of MG are at increased risk of regurgitating their food and developing aspiration pneumonitis (this happens when food, water, or saliva is inhaled into the lungs causing inflammation and secondary infection). Dogs and cats with megaesophagus must be closely watched during and after meals as aspiration pneumonitis can lead to death. Your vet will likely recommend elevating food and water bowls so that gravity will help to pass the food and water to the stomach. Your vet will also recommend a special high-quality diet and smaller, more frequent meals.

In some cases, MG can improve after a few months or years of treatment. Your vet can submit the specific test (mentioned above under ‘Diagnosing MG’) to monitor your pet’s progress.

Treatment for Pets with Myasthenia Gravis

Treatment is available in the form of oral medication. Pets typically have a good response to the medicine as long as they don’t have concurrent megaesophagus. Other medications that suppress the immune system can work as well. If the patient experiences regurgitation then the vet will recommend the best way to give food and medicines so that they will be absorbed.

When to Contact a Vet

If you notice any of the signs or symptoms listed above or your pet has previously been diagnosed with MG and is experiencing any problems, you should contact your pDVM (primary veterinarian).

Patients that inhale food, water, or saliva into the lungs need immediate veterinary care. This often includes hospitalization, medications including antibiotics, and oxygen if needed.

Read more:

Everything You Need to Know About Vomiting in Dogs

Warning Signs of Cancer in Dogs

Nothing to bark about! Causes of Limping in Dogs (and what you should do!)

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Published: 5/6/2021
Dr. Denise Michanowicz, Veterinarian

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