Myasthenia Gravis in Dogs: Symptoms and How It’s Diagnosed

Myasthenia gravis in dogs is an autoimmune disease that causes muscle weakness by disrupting the normal communication between nerves and muscles. 

While the condition can affect dogs of any age or breed, early diagnosis and treatment can help manage symptoms, improve quality of life, and reduce the risk of serious complications such as megaesophagus and aspiration pneumonia. 

Understanding the signs of myasthenia gravis can help you know when it’s time to seek veterinary care. 

What Is Myasthenia Gravis in Dogs?

Myasthenia gravis (MG) in dogs is an autoimmune disease that causes varying degrees of muscle weakness. 

Myasthenia gravis in dogs interferes with your pet’s nerves and the way these nerves should communicate with muscles to provide normal body movements and normal muscle contractions. 

Nerves transmit signals to the muscles. However, with myasthenia gravis in dogs, they don’t make it to the muscle properly. 

The immune system makes antibodies that destroy and block the receptors (called acetylcholine receptors) for the nerve signal. Because of this failure, nerves can’t do their job, which is to contact muscles for body movement. 

In addition to muscle weakness, this condition can also affect a dog’s mental state because it can be quite debilitating. If your dog is exhibiting any changes in their physical or mental condition, they should be seen by their veterinarian as soon as possible. 

Types of Myasthenia Gravis in Dogs 

There are three forms of myasthenia gravis in dogs: 

1. Generalized myasthenia gravis: In this type of myasthenia, all the skeletal muscles are affected. These dogs are often weak and rapidly fatigue while walking or exercising. 
2. Focal myasthenia gravis: The muscles of the face, head, and neck are affected most often by this type of myasthenia. These pups may have drooping of their face, trouble swallowing, frequent regurgitation, and experience changes to their bark. 
3. Fulminant myasthenia gravis: This is the worst kind of myasthenia gravis. Dogs affected with the fulminant form are often limp, get aspiration pneumonia, and become paralyzed. 

Symptoms of Myasthenia Gravis in Dogs

Let’s look at symptoms of myasthenia gravis in dogs. 

Generalized Myasthenia Gravis in Dogs 

This form affects 57% of dogs with acquired myasthenia gravis and symptoms may include: 

• Exercise-induced stiffness that resolves with rest 
• Tremors 
• Weakness 
• Excessive fatigue 
• Megaesophagus 

Focal Myasthenia Gravis in Dogs 

• Weakness in the muscles of the face, throat, and esophagus 
• Drooping of the facial muscles 
• Drooling 
• Trouble swallowing 
• Change in bark 
• Weakness in a specific part of the body 

Fulminant Myasthenia Gravis in Dogs 

• Sudden, decreased muscle tone 
• Megaesophagus 
• Rapid progression of paralysis in muscles that control a dog’s breathing  

If you believe your dog is experiencing any of the above symptoms, contact an emergency veterinarian immediately. 

Causes of Myasthenia Gravis in Dogs

Myasthenia gravis in dogs can be both inherited (genetic) or acquired. Acquired MG is more common than inherited myasthenia gravis in dogs. 

MG does not just occur in dogs and cats; it can also affect humans. The neuromuscular disease is caused by a deficiency in the acetylcholine receptors found on the surface of muscle cells. 

This deficiency causes signals between nerves and muscles to be interrupted, leading to muscle weakness in different areas of the body. The muscle weakness then leads to extreme fatigue within the dog.   

The following breeds are predisposed to inherit congenital myasthenia gravis in dogs, meaning they’re more likely to be born with the condition: 

• Jack Russell Terriers 
• English Springer Spaniels 
• Smooth Fox Terriers 
• Smooth-Haired Miniature Dachshunds 
• Samoyeds 

Dogs with inherited MG are born with fewer receptors and tend to be diagnosed when they are less than 1 year old. 

Acquired MG is more often seen in older dogs, including: 

• Newfoundlands 
• Great Danes 
• Golden Retrievers 
• Akitas 
• Scottish Terriers 
• German Shepherds 
• Labrador Retrievers 

Acquired MG can occur because of environmental, infectious, or hormonal influences. 

These influences negatively affect the immune system and cause antibodies to be produced against the receptors, thus preventing muscle movement. 

This immune response is typically seen in dogs with chest tumors (thymoma) and can be associated with hypothyroidism. 

How Veterinarians Diagnose Myasthenia Gravis in Dogs

Veterinarians diagnose myasthenia gravis in dogs by using blood tests that measure antibodies against acetylcholine receptors, along with clinical signs and additional diagnostic testing. 

If your dog is showing any changes in their physical or mental ability, they should be seen by their vet as soon as possible. 

It’s also a good idea to take a video of your dog’s behaviors to show your vet, in case your pup doesn’t show any signs at their appointment, such as exercise-induced symptoms. 

To diagnose myasthenia gravis and check for related complications, you veterinarian may perform the following tests: 

• Complete physical exam
• Blood work, including thyroid hormone levels: Elevated blood levels of antibodies against acetylcholine receptors can confirm an MG diagnosis, and the results are also used to monitor your dog’s response to treatment. Since this blood test needs to be sent to a laboratory, it may take up to a few weeks to get the results.
• Tensilon test: If MG is suspected by your vet based on the pup’s clinical signs and/or the breed of dog, a Tensilon test can be ordered while waiting for the blood test results. This  test involves an IV injection that temporarily and immediately improves weakness and other symptoms in affected dogs. Unfortunately, this injection and relief of symptoms only last for a few minutes.
• Chest X-rays: Chest X-rays are also important to check for megaesophagus, aspiration pneumonia, or cancer. Aspiration pneumonia occurs secondary to regurgitation and muscle weakness in the throat.

Treatment of Myasthenia Gravis in Dogs

Myasthenia gravis in dogs can’t be cured, but it can be treated and successfully managed. 

Treatment depends on the type of MG diagnosed in your dog and the symptoms associated with that type. 

If your dog has been diagnosed with MG, the most common medication used for treatment is pyridostigmine bromide. 

This medication will improve your pup’s muscle function by increasing the amount of time acetylcholine stays in the receptors on the muscle cells to coordinate movement. 

Prednisone or other steroid medications can also be used because they help suppress the immune system, thus suppressing the response that is causing MG. 

If your dog is diagnosed with associated hypothyroidism, levothyroxine sodium will most likely be prescribed for the rest of their life to help manage the condition. 

Dogs with megaesophagus need to be fed their meals in a very special manner. 

They must be fed in an elevated food bowl or in a special Bailey chair to keep them upright. 

This chair helps to avoid inhalation of their food, which could result in aspiration pneumonia. 

It is recommended that pups with this condition be fed small meals frequently during the day instead of two large meals. Dogs with megaesophagus should also be kept standing upright on their hind legs or in the special chair for 20 to 30 minutes after eating. 

If the dog has a thymoma tumor, surgery may be an option to remove it if they are determined to be healthy enough for the operation.  

Recovery and Management of Myasthenia Gravis in Dogs

The prognosis for myasthenia gravis in dogs varies depending on the type of MG, underlying causes, and whether complications like aspiration pneumonia are present. 

A diagnosis of MG is typically serious, and some dogs need lifelong treatment. 

However, if it is caught and treated early, remission in dogs with myasthenia gravis can be reached after several months. 

Dogs who have aspiration pneumonia have a less favorable prognosis, especially if they have breathing complications or chest tumors. 

Prevention of Myasthenia Gravis (MG) in Dogs

There are no known ways at this time to prevent myasthenia gravis in dogs.