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Myasthenia gravis and the role of the veterinary nurse
Abstract
Myasthenia is a syndrome of impaired neuromuscular transmission which can affect dogs and cats. There are two common forms, an autoimmune form where antibodies work against the neuromuscular junction – myasthenia gravis – and a rare, congenital form where the patient is born with an impairment at the neuromuscular junction, for example, they are born with too few acetylcholine receptors. This article focuses on myasthenia gravis. Patients with myasthenia gravis often also develop secondary pathologies such as megaoesophagus and aspiration pneumonia, requiring intensive supportive care from the veterinary team while hospitalised, owner counselling and support being paramount. This article describes the causes, diagnosis and treatment alongside nursing considerations for the myasthenia gravis patient and a brief discussion about future developments around the disease to help the veterinary nurse to be able to assist in better patient outcomes following a diagnosis of myasthenia gravis.
Immune-mediated myasthenia, also known as myasthenia gravis, is a fairly common neuromuscular disease affecting dogs and occasionally cats. The dog breeds most often affected are German Shepherds, Labradors, Golden Retrievers, Akitas, Great Danes and Newfoundlands. The Abyssinian and Somali cat breeds are more predisposed than other feline breeds, but the disease can affect any canine or feline breed (Vercesi, 2021). While there is some literature to support the concept of genetic predisposition for the disease, this is an area that requires further research to confirm (Wolf et al, 2017). Myasthenia gravis can be seen at any age over 3 months, but more commonly occurs between 5 and 7 years of age, and neutered female dogs are at a higher risk than males (Platt and Shelton, 2017).
The aetiology of myasthenia gravis is a disruption to neuromuscular transmission. In a neurologically normal patient, acetylcholine is released from the presynaptic vesicles, which are located in the axon terminal of the motor neuron, where it then binds with receptors on the endplate of the muscle fibre membrane. However, in patients with myasthenia gravis, the receptors are targeted by autoantibodies, so the acetylcholine is unable to bind and therefore the muscles do not get the signal to contract. This causes progressive weakness and fatigue which can occur focally or generalised to the point that the patient becomes non-ambulatory.
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