Because dogs are living creatures who lick us, love us, and go for walks with us, we can easily overlook that their bodies — like our own — are extremely complex organisms. When we look beneath the fur, the wagging tail, or the lolling tongue, it is consistently astonishing just how many interdependent systems must function properly just for a dog to go for a walk. Every movement and every step requires not only energy and muscles, but also a series of electrochemical signals that deploy that energy and tell muscles to expand or contract.
On a micro level, moving this involves a series of messages that must travel from the central nervous system to the skeletal muscles, which control voluntary movement. Issued by the spinal cord via the brain, these messages move through the nervous system until they reach the muscle that is being instructed to move. The last part of that journey is a neuromuscular junction, a gap between the final neuron and the muscle itself.
The message itself is conveyed by a chemical called acetylcholine, which must ford the gap between the neuron and the muscle. Sometimes that message is prevented from arriving by a condition called Myasthenia Gravis.
Acquired Myasthenia Gravis in dogs is an autoimmune disorder in which those signals do not arrive at their destination. The muscle’s acetylcholine receptors are attacked and blunted by antibodies, after which they are unable to receive the message to move. The longer the condition persists, the weaker the affected muscles become. A dog with Acquired Myasthenia Gravis begins to display what is referred to as generalized weakness; such a dog may seem to get tired after very little exertion.
In reality, it is not that the dog is getting tired faster, it is that its muscles are simply not receiving the chemical messages telling them to move. This leaves us with a number of questions:
What we do know is that antibodies attack and destroy acetylcholine receptors on the surface of muscles. We also know that there are a range of other health issues, conditions, or problems that have been observed in dogs with Acquired Myasthenia Gravis. The condition has been seen in dogs with neoplasms — growths or tumors, whether they are malignant or not — of the bile duct, anal gland, esophagus, uterus, and the thymus.
It is also linked with a number of other deficiencies, many of which primarily affect female dogs. Unsurprisingly, there is a much higher incidence of Acquired Myasthenia Gravis in the female dog population. Slow blood clotting, early destruction of red blood cells, insufficient production of hormones by the adrenal glands, and underactive thyroid are some of the disorders that are seen in cases where Acquired Myasthenia Gravis is diagnosed.
While we know that these other diseases, disorders, and deficiencies appear in dogs who have Acquired Myasthenia Gravis, they are generally coincidental. What we do not know is exactly what it is that spurs a dog’s own immune system to attack neuromuscular junctions, preventing muscles from receiving messages from the central nervous system.
Diagnosing the condition can be difficult, since it appears suddenly in its acquired form — there is also a congenital one that appears in very young puppies — and because there are four different forms that canine Myasthenia Gravis can take.
For a dog who is typically healthy and energetic, the most telling sign of Acquired Myasthenia Gravis is when the dog gets tired quickly after very little exercise. Energy and movement come in spurts for afflicted dogs. After a burst of energy, they may get tired and rest, and repeat this cycle of activity and weakness. It can affect the entire body, or be more pronounced in the hind legs.
The other major symptom of the condition is megaesophagus. When the esophagus functions normally, its muscles expand and contract as the dog eats, pushing food down into the stomach. A dog suffering from Acquired Myasthenia Gravis will frequently regurgitate his food. It’s important not to confuse regurgitation with vomiting. In this instance, vomiting means foods or liquids that come back up after being in the stomach and partially broken down. Regurgitated food, on the other hand, has yet to reach the stomach at all.
Symptoms of Myasthenia Gravis tend to surface in very young or very old dogs. Most reported cases of the autoimmune disorder appear in dogs between 1 to 4 years of age, or in those from ages 9 to 13. The average ages for a diagnosis are 3 and 10 years old. Size and relative hardiness of dogs is irrelevant, since the list of breeds at higher risk for developing the neuromuscular condition are seemingly random. These include:
Treating this disorder is tricky as well, since it is frequently a secondary problem that appears due to other health issues. If there is an underlying deficiency in clotting, hormone production, or underperforming thyroid, that problem will have to be addressed as well. The other factor that can hinder treatment is that symptoms of Acquired Myasthenia Gravis can disappear as suddenly as they surfaced. According the the Veterinary School at UC Davis:
Up to 87.7% of affected dogs will go into spontaneous remission at an average of 4 months after diagnosis.
Depending on the severity of the condition, an afflicted dog may require short-term hospitalization and regular daily palliative care, including help eating, breathing, and drugs to suppress the immune system to prevent further degeneration of acetylcholine receptors. This, of course, means weakening the dog in order to help it get stronger in the long term.
For many dogs, the symptoms of this debilitating neuromuscular condition resolve themselves, so the key is getting an accurate diagnosis quickly and providing the correct medications until remission occurs. Acquired Myasthenia Gravis is a complicated disorder, and there are no simple answers or approaches. If you have, or have had, a dog who suffered from this condition, feel free to share your experiences in the comments, along with support groups, forums, or communities that you have turned to.
About the author: Melvin Peña trained as a scholar and teacher of 18th-century British literature before turning his research and writing skills to puppies and kittens. He enjoys making art, hiking, and concert-going, as well as dazzling crowds with operatic karaoke performances. He has a two-year-old female Bluetick Coonhound mix named Baby, and his online life is conveniently encapsulated here.