Interesting Cases

Myasthenia Gravis

Emma Behan is usually a very energetic, happy, two year old, lab and basset hound mix. Emma is always bouncy and affectionate. She loves to chase birds, fetch toys, play with other dogs and steal tissues. Her owners, Eileen and Mike were very distressed when overnight she started coughing and drooling and became extremely lethargic. She could hardly stand or walk and would not even eat. Luckily, Eileen, who is one of our wonderfully observant and knowledgeable veterinary assistants, realized just how seriously ill Emma was brought her in for an exam immediately the next morning.

At the hospital, Emma looked like a very sick little girl. Her mucous membranes were pale and and she was coughing. She drooled continuously and all her legs were shaking when she stood. She was so weak that her head hung low from her long neck. Her face had a very blank expression and later we realized that the muscles that control Emma’s face and head were not working.

We were concerned that Emma had a serious respiratory infection, like the dog flu or a bacterial infection like leptospirosis, however, she had very little contact with other dogs or animals, was not boarded recently and she also had no fever. A toxin, like rat poison, may have caused the symptoms she exhibited, but Mike and Eileen could not think of any toxin that Emma could encounter in her environment.

We gave Emma intravenous fluids, antibiotics and ran screening blood tests which were normal. A chest radiograph showed that Emma had aspiration pneumonia and it became obvious that she was regurgitating food and fluid from her stomach into her esophagus and mouth.

There are very few diseases in young, healthy dogs that cause very sudden muscle weakness and regurgitation and pneumonia. Myasthenia Gravis (MG) is an immune disease in which the body attacks the neurotransmitter sites between the nerves and the skeletal muscles. Because the chemical signals cannot travel from the nerves to the muscles, the muscles are weak and tire very easily. A dog’s esophagus has skeletal muscle and becomes dilated with MG. Regurgitated fluid then is accidentally inhaled into the lungs, causing pneumonia.

Emma improved immediately on pyridostigmine, a medication that prolongs the action of the chemicals or neurotransmitters that allow nerves to communicate with muscles.

Emma’s case is more rare because the test used to diagnose MG was negative and this only occurs in 2% of all cases.

Emma continues to do very well and we hope that in six months, her disease will go into permanent remission.

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