Dogs with Myasthenia Gravis

Portrait of dog, lying on sofa

Myasthenia gravis is a complicated condition that can make your dog very weak and exhausted. The condition causes a breakdown in communication between the muscles and nerves, leaving the dog weak and unable to perform basic tasks. Myasthenia gravis is a condition that can be inherited or acquired, but it requires medicine to manage.

What is Myasthenia Gravis?

Myasthenia gravis is a neuromuscular disease that affects both dogs and cats. A lack of acetylcholine receptors on the surface of the muscle cells causes it. A lack of appropriate ACh-receptors affects nerve-muscle communication, resulting in muscular weakness in many regions of the body. There can be no efficient signal transmission between muscles and neurons unless there are enough ACh-receptors.

Symptoms of Myasthenia Gravis in Dogs

If you suspect your dog is suffering from myasthenia gravis or another condition, call your veterinarian immediately. Myasthenia gravis causes muscular weakness that can be widespread (all throughout the body) or localized (only appearing in specific areas of the body). The most often afflicted focus regions are Signs might be minor to severe in any instance. Other than weakness, dogs with myasthenia gravis may show the following signs:

Symptoms

  • Exercise intolerance
  • Sudden collapse or falling over/paralysis
  • Sleeping with eyes open
  • Drooping of eyelids
  • Excessive drooling
  • Trouble swallowing
  • Regurgitating 
  • Difficulty breathing and coughing
  • Changes in bark or whine
  • Tumor in chest


Exercise Intolerance

Myasthenia gravis can cause generalized muscular weakness in certain dogs, which manifests as activity intolerance or weakness that improves with rest. Some dogs just get weaker over time, have difficulty walking, and tire easily.

Sudden Collapse or Falling Over/Paralysis

On the opposite extreme, some dogs can develop sudden paralysis due to myasthenia gravis.

Sleeping With Eyes Open

One of the most debilitating functions that a dog will lose with this disease is its ability to blink. This may result in your pet sleeping with its eyes involuntarily open.

Drooping of Eyelids

Myasthenia gravis affects the muscles of the face, including the upper eyelids. Your dog may begin to have drooping eyelids, in addition to the inability to blink, as a result.

Excessive Drooling

Your dog will begin to lose control of its lips and mouth. Your dog may experience excessive drooling, especially at the corners of its mouth.

Trouble Swallowing

A dog's difficulty in swallowing can cause it to inhale food, liquids, and its own vomit. Or the dog will begin to excessively swallow in an attempt to try to control the loss of function.

Regurgitating

Your dog's esophagus will be affected by the illness, resulting in a secondary ailment known as (enlargement of the esophagus). The tube connecting the throat and the stomach, the esophagus, will lose its capacity to transfer food into the stomach. Because the contractions do not operate, a dog with acquired myasthenia gravis will ingest food, but it will become stuck in the esophagus or spit back up into its mouth without retching or vomiting. When food or liquid is aspirated into the lungs and an infection develops, can quickly progress to aspiration pneumonia.

Difficulty Breathing/Coughing

Problems with swallowing can result in difficulty breathing, coughing, and can lead to the development of aspiration pneumonia.

Changes in Bark or Whine

The condition weakens a dog's laryngeal muscles. As a result, its voice, including its bark and whine, will begin to change.

Tumor in Chest

Acquired myasthenia gravis may also cause some dogs to develop a type of tumor in the chest called a thymoma.

Causes of Myasthenia Gravis

Myasthenia gravis can be congenital (present at birth) or acquired. Although neither form is very common in dogs, the congenital form is rarest.

Puppies with congenital myasthenia gravis usually show symptoms between the ages of six and eight weeks. These canines were born with an insufficient number of ACh-receptors. They usually exhibit indicators of exercise-induced weakness, which can lead to paralysis and even death. Myasthenia gravis is more common in some dog breeds, such as:

Adult dogs get acquired myasthenia gravis around the age of two to four years. This kind of myasthenia gravis is caused by the immune system. Antibodies in the dog damage ACh-receptors, resulting in a deficit. Any dog can get acquired myasthenia gravis, however some breeds are more susceptible than others, including:

Diagnosing Myasthenia Gravis in Dogs

Your veterinarian will go through your dog's medical history with you before doing a complete physical examination. To search for underlying disorders, further diagnostics such as lab testing and radiographs (x-rays) may be needed. Before reaching a clear diagnosis, it's critical to rule out other diseases, ailments, or injuries. Your veterinarian may advise you to take your dog to a veterinary specialist (typically a veterinary neurologist) for further evaluation.

A specific blood test (AChR antibody test) can be done to check for antibodies against acetylcholine receptors. This test can effectively diagnose most dogs with myasthenia gravis.

If your dog's symptoms are obvious, a particular medicine to test for myasthenia gravis may be administered. This is referred to as a Tensilon test. Edrophonium, an acetylcholinesterase inhibitor, is administered intravenously to the dog. If the dog has myasthenia gravis, then the drug will cause a significant (though temporary) improvement in the muscle weakness.

Treatment

If your dog's symptoms are obvious, a particular medicine to test for myasthenia gravis may be administered. This is often called a Tensilon test. The dog is given an intravenous injection of an acetylcholinesterase inhibitor called edrophonium. If the dog has myasthenia gravis, the medicine will improve the muscular weakness significantly (but only temporarily).

  • Anticholinesterase agents: Pyridostigmine or neostigmine anticholinesterase agents are prescribed to enhance neuromuscular signal transmission. These drugs can prolong the action of acetylcholine at the neuromuscular junction. Dogs with acquired myasthenia gravis usually need to remain on this type of medication for life which may be enough to effectively manage their symptoms.
  • Immunosuppressive therapy: This type of therapy may be considered if additional treatment is needed. Because acquired myasthenia gravis is immune-mediated, immunosuppressive medications may be effective. Your vet may prescribe corticosteroids to suppress the immune system. However, immunosuppressive therapy can increase the risk of infections, especially for dogs with megaesophagus who are already prone to developing aspiration pneumonia.
  • Therapeutic plasma exchange: This treatment is sometimes used for humans with serious cases of myasthenia gravis. This is available for dogs in some regions but it may be cost-prohibitive. TPE involves removing the "diseased" plasma and replacing it with plasma from a healthy donor. This therapy may be effective in dogs with very serious cases of myasthenia gravis.
  • Hospital care: Following the diagnosis of myasthenia gravis, hospitalization may be necessary to stabilize your dog, especially if secondary issues are a concern. The hospitalization will also help your veterinarian closely monitor your dog during the medication adjustment period.

Supportive care is a major part of treating dogs with myasthenia gravis, which includes the following therapies:

  • Dogs with megaesophagus should be fed large "meatballs" of food while in an upright position. This type of feeding may allow food to get into the stomach more effectively and lessen the risk of aspiration pneumonia.
  • Fluid therapy may be required to avoid dehydration, particularly in dogs that regurgitate liquids. 
  • Medications to support the gastrointestinal system may also be helpful (metoclopramide, cisapride, cimetidine).
  • Antibiotics and breathing treatments (like nebulizers) may be necessary to treat aspiration pneumonia.
  • In serious cases of megaesophagus, a stomach tube may need to be surgically placed to deliver food directly to the stomach.

Prognosis for Dogs With Myasthenia Gravis

If your dog's symptoms are obvious, a test for myasthenia gravis may be administered. A Tensilon test is what it's called. Edrophonium, an acetylcholinesterase inhibitor, is administered intravenously to the dog. If the dog has myasthenia gravis, the medicine will improve the muscular weakness significantly (but only temporarily).

If your dog does not recover, you will need to take special care of him. Depending on the severity of your dog's illness, everyday care may be time-consuming (especially if your dog has megaesophagus). Try to follow the instructions below:

  • Pay close attention to details of your dog's behavior and communicate with your vet about any change in your dog, regardless of how small.
  • Be patient with yourself and your dog.
  • Ask for help from friends and family members if needed.
  • Join a community of fellow myasthenia gravis or megaesophagus dog owners for extra support.
  • Keep a log of daily medication and treatments so no steps in your dog's care are overlooked.

It is always potential for issues to arise, no matter how attentively you monitor your dog. Your dog may need to be hospitalized periodically to treat aspiration pneumonia or other secondary problems.

How to Prevent Myasthenia Gravis

Unfortunately, there are no preventative measures for this neuromuscular disease in dogs.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.

CITATION

"Myasthenia gravis in dogs | vca animal hospitals.", "Clooten JK, Woods JP, Smith-Maxie LL. Myasthenia gravis and masticatory muscle myositis in a dog. Can Vet J. 2003;44(6):480-483.", "Myasthenia gravis in dogs | vca animal hospitals.", "Allen M. Schoen MS. World small animal veterinary association world congress proceedings, 2011VIN.com. Published online March 30, 2015." ;

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