Myasthenia Gravis in Dogs

Myasthenia gravis is a condition that negatively impacts the way a dog’s nerves relay messages to their muscles. This function is referred to as a neuromuscular transmission and when things start to go wrong, dogs show signs of fatigue and weakness. Myasthenia gravis is a disorder that puppies are born with, in short it is congenital. It is also a familial disorder which means lines with condition will pass it on to their offspring with some breeds being more predisposed to inheriting myasthenia gravis than others.

Breeds Most at Risk

As previously mentioned, certain breeds appear to be more at risk of inheriting the condition that others which includes the following:

• Jack Russell
• English Springer Spaniel
• Smooth Fox Terrier
• Smooth-haired Miniature Dachshund
• Newfoundland – the breed suffers from the familial form of the disorder
• Great Dane – the breed suffers from the familial form of the disorder

All the above breeds are known to have the autosomal recessive gene responsible for myasthenia gravis. However, the condition can also be acquired and like other autoimmune diseases, dogs usually develop the disorder because of a genetic link.

The Causes

It is thought that several factors can play a part in why myasthenia gravis affects certain breeds more than others and this includes for the following reasons:

• Environment
• Infection
• Hormonal issues
• Tumours and cancer and in particular, thymus tumours
• Immune-mediated diseases
• Congenital - present at birth

The breeds that appear to be the most affected by the acquired form of myasthenia gravis include the following:

• German Shepherd
• Labrador Retriever
• Dachshund
• Scottish Terrier
• Akita

Symptoms Associated with the Disorder

Dogs with the congenital form of the disorder start to show signs of there being something wrong with them when they are anything from 6 to 8 weeks old. However, dogs suffering from the acquired form can show signs of there being something wrong when they are anything from 1 to 4 years old or even later in life when they reach 9 to 13 years old. Younger females are at a slightly greater risk of developing the acquired form of the disease, but not when they are older.

The symptoms associated with the acquired form of the disorder are as follows:

• Muscles in the oesophagus are affected
• Muscles in the throat are affected
• Muscles around the eyes are affected
• Collapse

The symptoms associated with the acquired form are typically as follows:

• A swollen oesophagus
• Normal reflexes are negatively impacted
• A mass develops on a dog's chest typically at the front
• Regurgitation
• A change of voice
• Exercise intolerance
• Weakness which gets progressively worse
• Cramping
• Fatigue
• Acute collapse
• Dogs sleep with eyes open
• Drooling excessively
• Difficulty swallowing
• Aspiration pneumonia

Diagnosing the Problem

It can prove challenging for vets when it comes to diagnosing the condition partly because there are other neuromuscular transmission disorders with very similar symptoms. As such, a vet would need to rule these out before coming to a definitive diagnosis. The vet would ideally need to have a dog's full medical history and be told how the first signs of there being something wrong first presented themselves. A dog suspected of suffering from myasthenia gravis would be thoroughly examined with the vet carrying out certain tests which help confirm a diagnosis. The tests a vet would carry out would include the following:

• A complete blood count
• A full chemical blood profile
• A urinalysis
• Test thyroid function
• X-rays which would establish if a dog's oesophagus is enlarged and if they are suffering from aspiration pneumonia
• Ultrasound which would determine if there are any growths in a dog's chest cavity
• A biopsy to confirm if a growth is cancerous

Treatment Options

Dogs suffering from myasthenia gravis would need to be hospitalised so their condition can be closely monitored and they can be given all the supportive care needed to stabilise their condition. This often means being fed a high calorie diet via a tube. Dogs also need to be given oxygen therapy along with a course of antibiotics. Should a dog have developed aspiration pneumonia, their condition must be monitored and treated as a matter of urgency. If a dog has developed a tumour, the vet might suggest surgically removing the growth once they have the results of the biopsy.

Living with a Dog with Myasthenia Gravis

Once a dog's condition has been diagnosed and they have responded well to a treatment, their muscle strength usually returns over time. However, they would need to be taken back to the vet for regular check-ups when more chest X-rays might be necessary to ensure their oesophagus has not become enlarged again. The vet would also carry out more blood tests to ensure their antibodies are back to normal.