Q: Would you give a description of myasthenia gravis, please? It is fairly rare and often thought to be Parkinson’s.
A: Myasthenia is not as rare as most people think. It often goes undiagnosed for some time or is mistaken for muscular dystrophy, multiple sclerosis, or Parkinson’s disease.
It is the most common primary disorder of the nerve endings that control muscle movement. It usually affects women aged 20-50, which is why it can be confused with MS. However, unlike multiple sclerosis and muscular dystrophy, it does not lead to muscle wasting or degeneration.
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Myasthenia gravis is characterized by a lack of the neurotransmitter substance, acetylcholine, at the nerve endings in a muscle. It is believed the disease is caused either by an acquired disorder of the immune system, an autoimmune disease or by some genetic abnormality. In rare instances it can be the result of an abnormality of the thymus gland.
Early symptoms of the disease are general muscle weakness, especially in the eyes, face and neck. People complain they have difficulty holding their eyes open, even when they are not sleepy, although fatigue is also a problem usually later in the day. Those with a more advanced case may have difficulty swallowing, chewing or speaking. They may also suffer double vision.
All these symptoms can be worsened by emotional stress, pregnancy or untreated thyroid disease. Patients who already suffer from other autoimmune diseases, such as thyroid disease, lupus or rheumatoid arthritis, may be more likely to get myasthenia.
To help make the diagnosis, a doctor can perform a blood test to see whether you have high levels of acetylcholine receptor antibodies. This test is usually a good indicator of the disease, but sometimes people with just the droopy eyelid symptom may not have a positive blood test. A neurologist can do a nerve conduction study. In this test the muscles are jolted with a small electric current to see which respond appropriately. It is not painful.
A more definitive test is to inject a drug called Tensilon. It temporarily increases the levels of acetylcholine with a dramatic sudden increase in muscle strength in those with the condition. In normal individuals, it will not make any difference. You cannot use this drug to become a champion weight lifter.
An MRI of the chest area may help to determine if there is an abnormality or tumour in the thymus gland.
There are some treatments available. Anticholinesterase drugs are used to block the breakdown of acetylcholine at the nerve endings. They work by inhibiting the enzyme cholinesterase. Based on the theory that this is an autoimmune disorder, immunosuppressants such as prednisone may also be used. However, steroids such as prednisone are not my favourite medications due to the large number of unpleasant or potentially dangerous side effects, but it can help the weak muscles regain their strength. The effect may be only temporary.
Clare Rowson is a medical doctor with a practice near Belleville, Ont. Her columns are intended for general information only. Individuals are encouraged to also seek the advice of their own doctor regarding medical questions and treatments.
