Myasthenia Gravis Support Group

Myasthenia gravis (MG) is a neuromuscular disease leading to fluctuating muscle weakness and fatiguability. At about 14 cases per 100,000 (in the U.S.), it is one of the lesser known autoimmune disorders. The antigens and basic disease mechanisms are known. Weakness is typically caused by circulating antibodies that block acetylcholine receptors at the post-synaptic neuromuscular junction, inhibiting the stimulative effect of the neurotransmitter acetylcholine. Myasthenia is treated with immunosuppressants, cholinesterase inhibitors and, in selected cases, thymectomy.

The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest. Muscles that control eye and eyelid movement, facial expression, chewing, talking, and swallowing are especially susceptible. The muscles that control breathing and neck and limb movements can also be affected. Often the physical examination is within normal limits.

Although myasthenia gravis may affect any voluntary muscle, muscles that control eye and eyelid movement, facial expression, and swallowing are most frequently affected. The onset of the disorder may be sudden or rapid. Symptoms often are not immediately recognized as myasthenia gravis; a proportion only receives a diagnosis after more than a year.

In most cases, the first noticeable symptom is weakness of the eye muscles. In others, difficulty in swallowing and slurred speech may be the first signs. The degree of muscle weakness involved in myasthenia gravis varies greatly among patients, ranging from a localized form, limited to eye muscles (ocular myasthenia), to a severe or generalized form in which many muscles - sometimes including those that control breathing - are affected. Symptoms, which vary in type and severity, may include asymmetrical ptosis (a drooping of one or both eyelids), diplopia (blurred or double vision) due to weakness of the muscles that control eye movements, unstable or waddling gait, weakness in arms, hands, fingers, legs, and neck, a change in facial expression, dysphagia (difficulty in swallowing) and shortness of breath, and dysarthria (impaired speech, often nasal due to weakness of the pharyngeal muscles).

Myasthenia gravis can usually be controlled with medication. Medication is used for two different endpoints: Direct improvement of the weakness, and reduction of the autoimmune process

Muscle function is improved by cholinesterase inhibitors, such as neostigmine and pyridostigmine. These slow the natural enzyme cholinesterase that degrades acetylcholine in the motor end plate; the neurotransmitter is therefore around longer to stimulate its receptor.

Immunosuppressive drugs such as prednisone, ciclosporin and azathioprine may be used. If the myasthenia is serious (myasthenic crisis), plasmapheresis is used to remove the putative antibody from the circulation. Similarly, intravenous immunoglobulins (IVIg) is used to bind the circulating antibodies.

Thymectomy, the surgical removal of the thymus gland (which is abnormal in myasthenia gravis patients), improves symptoms in more than 50 percent of patients, even in those without thymoma. Some patients are cured by thymectomy, suggesting that the thymus plays a significant role in the pathogenesis of myasthenia.