Myasthenia Gravis

Description

Myasthenia gravis is a disease of the neuromuscular junction that occurs due to a defect or absence of nicotinic acetylcholine receptors on the post-synaptic membrane (in the congenital form) or due to the presence of antibodies that bind to the receptors and prevent them from functioning normally (in the acquired form). Acquired myasthenia Gravis is the most common form of the disease. The classical focal form of myasthenia gravis affects only the extraocular muscles, the cranial oesophagus and the muscles innervated by cranial nerves V, VII and IX. 80% of animals diagnosed with myasthenia gravis have megaoesophagus at presentation.

Signalment

Akitas, German shorthaired pointers, Chihuahuas and some terrier breeds are predisposed to the disease, however Labradors and Golden retrievers are frequently diagnosed with the disease. Dogs 2-3 years old and also older than 9 years old are more commonly affected by the disease.

Abyssinian and Somali are the most commonly affected cat breed and can be affected at any age.

Clinical Signs

Three types of disease have been reported in the dog.

• Focal
• Chronic generalized
• Acute fulminant generalized

References

Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company

• Animals develop antibodies to nicotinic acetylcholine receptors.
• Results in generalised muscle weakness and or megaoesophagus.

Pathogenesis: Type II hypersensitivity