Canine Myasthenia Gravis Diagnosis

Canine mysathenia gravis is a neuromuscular disorder that can limit your dog's mobility and inhibit major body functions. Myasthenia gravis affects the motor nervous system, causing muscle weakness. Here's what you should know about myasthenia gravis symptoms and diagnosis.

Myasthenia Gravis in Dogs Explained

Myasthenia gravis is a disease of the motor nervous system. It doesn't affect your dog's sensory nerves, but it can severely limit his mobility and other physical functions, like swallowing.

In a normal dog's nervous system, the nerve endings secrete the neurotransmitter known as acetylcholine, which carries messages from one nerve ending to another and tell the dog's muscles to move. When canine myasthenia gravis occurs, the number of nerve receptors for acetylcholine in your dog's brain diminishes, leaving your dog susceptible to muscle weakness.

There are two common types of myasthenia gravis. Congenital myasthenia gravis is hereditary, and occurs when a dog is born without the appropriate number of acetylcholine receptors in his brain. Acquired canine myasthenia gravis is a type of autoimmune disorder that attacks and damages aceltycholine receptors. 

Myasthenia Gravis Symptoms

Most dogs experience the muscle weakness of myasthenia gravis in the legs, especially the hind legs. Dogs may have trouble rising from a reclining position, or jumping. They may wobble and sway when they walk.

Dogs with myasthenia gravis seem to tire easily from only gentle exercise. They may experience muscle weakness in the throat, eyes and face as well as in the legs. They may experience megaesophagus, an enlarging of the esophagus that causes voice changes, frequent regurgitation, weight loss and trouble swallowing. Megaesophagus increases your dog's chance of inhaling a foreign object into the lungs; if this happens, your dog could experience the lung infection known as aspirant pneumonia, a life threatening condition. 

Diagnosing Myasthenia Gravis

Your vet will need a complete medical history and a thorough physical exam in order to diagnose myasthenia gravis. Your vet may perform a number of neurological tests to determine the extent of your dog's motor function. Your vet will test your dog for the muscle weakness associated with myasthenia gravis. 

Your vet may choose to test for myasthenia gravis by injecting your dog with edrophonium chloride. This drug raises the levels of acetylcholine in your dog's brain, and can help to increase muscle strength and motor function. If your dog responds positively to the injection and regains some muscle strength and motor function, he'll most likely be diagnosed with myasthenia gravis.

Treating Myasthenia Gravis

Your vet can treat the symptoms of myasthenia gravis by injecting your dog with edrophonium chloride and other drugs that increase levels of acetylcholine in the brain. These drugs can help your dog regain muscle strength and function. Other drugs used to treat myasthenia gravis include corticosteroids like prednisone, pyridostigmine and azathioprine.

Some dogs may experience remission from myasthenia gravis. Even without treatment, most dogs experience a remission of symptoms within about 18 months of onset. However, even if your dog goes into remission, he could suffer recurrent bouts of the disease throughout his life and continue to require treatment.