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Canine myasthenia gravis is a rare disease that attacks the motor nerves of dogs. It causes weakness in the muscles, but it leaves the sensory nerves undamaged. Canine myasthenia gravis is specifically caused by a deficiency of certain receptors, acetylcholine receptors, that are usually found where the nerve endings join with the cells of the muscles.
In order to understand canine myasthenia gravis, it is important to know how a dog’s nervous system and muscular system work and how they are connected. The process begins when the dog decides that he wants to move. In a healthy dog, the nerve endings release a neurotransmitter, acetylcholine. The neurotransmitter – acetylcholine – then carries the nerve impulse to the acetylcholine receptors which respond appropriately and send the nerve impulse on to the brain and muscles. Therefore, the dog moves.
With canine myasthenia gravis, there is a decrease in the number or sometimes the function of the acetylcholine receptors. This makes the muscles of the dog weak, particularly in the hindquarters. For example, he may have problems standing up when he has been laying down. He can also sway or stagger when he walks. Canine myasthenia gravis is worse when the dog has been engaging in light exercise.
Although canine myasthenia gravis most commonly affects the legs, there are also several other kinds. For example, the focal kind of canine myasthenia gravis affects only the muscles that allow the dog to swallow. Consequently, if he is affected by the focal form, the dog will not be able to swallow solid food. This can lead to a swollen esophagus and eventually a form of pneumonia. Other kinds include a congenital form that only affects Jack Russell Terriers, Springer Spaniels, and Smooth Fox Terriers and an acquired form that is most common in Golden Retrievers, German Shepherd Dogs, Dachshunds, Labrador Retrievers, and Scottish Terriers.
Canine myasthenia gravis is diagnosed after the dog has a neurological examination at his veterinarian’s office. There are several different tests that can be completed to check for the disease. In one test, the dog is injected with edrophonium chloride. The drug prevents the enzyme that breaks down the acetylcholine. As a result, there are higher concentrations of acetylcholine at the acetylcholine receptors. If the dog shows that he has increased his muscle strength after receiving the drug, then he has tested positive for canine myasthenia gravis.
Luckily, there are treatment plans for canine myasthenia gravis. The disease itself is treated by giving the dog drugs that raise the concentration of the acetylcholine at the receptors, much like the diagnostic test mentioned above. The drugs will reverse the muscle weakness and are usually injected into the dog. However, a veterinarian will likely want to monitor the dog and his progress until improvement is seen.