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VetInfo - Veterinary Medical Information for Dogs and Cats - M- Myasthenia Gravis

Myasthenia gravis is a neuromuscular disease in which weakness is the primary sign. This disease is caused by an inability of the certain nerve receptors (nicotinic acetylcholine receptors (AChRs) to function properly. This prevents the stimulus for muscles to contract which leads to the weak appearance. This disease occurs congenitally in some dog breeds. Jack Russell terriers, springer spaniels and smooth fox terriers are affected. It can also occur as an acquired problem in older dogs. In this case, it is thought to be an immune mediated disease. In older dogs, the first sign of problems may be megaesophagus -- enlargement of the esophagus due to the muscular weakness, leading to problems swallowing. This can cause regurgitation and lead to inhalation pneumonia.

Myasthenia gravis can be very variable in the way it looks. Only a few muscle groups may be affected or the dog may be nearly immobile. A dog can be almost normal after a rest and then lose strength very rapidly when it exercises at all.