Myasthenia Gravis

Signs and Symptoms

Transient or permanent weakness in some or all of the skeletal muscles and abnormal fatigue are the cardinal signs. In more than half of the patients, initial symptoms are related to the involvement of the eye muscles. The most frequent of these is [Page 1156]the ptosis, which is drooping of the eyelids. Gaze parezies and diplopia may also be observed. Ptosis or weakness in other muscles may be symmetrical or asymmetrical and characteristically shows fluctuation during the day or from day to day. Symptoms are typically heavier toward evening and after physical activity and tend to improve in morning hours and after rest.

If the disease is restricted only to the eyes, it is called ocular myasthenia; this is a more benign form of the disease, but unfortunately, only 14 percent of all the myasthenic patients are in this group. In most of the patients, the disease becomes “generalized.” This means that extremity muscles and/or “bulber muscles,” in other words, muscles related to the respiration and swallowing functions, are also involved. Extremity muscles are affected later typically, muscles in the face, chin, tongue, and muscles related to swallowing may be heavily affected when there is no or very slight involvement of the extremity muscles.

A patient with generalized myasthenia typically has ptosis, and facial weakness causes a special “myasthenic” facial appearance. Difficulty in swallowing and in talking is seen, which is called “nasal talking.” When the disease becomes worse, trunk, abdominal, and respiration muscles are involved. As a result, difficulty in respiration and coughing occurs, and this results in the accumulation of the secretions and development of pulmonary complications such as bronchitis, atelectasia, and pneumonia.

Most of the myasthenic patients show intermittent worsening periods; these are mostly related to the upper respiratory tract infections. If the exacerbation is severe and there is a requirement for endotracheal entubation and respiratory support, this situation may be called a “myasthenic crisis.” Neonatal myasthenia may be present in 12 percent of infants born to myasthenic mothers due to antibodies passively crossing the placenta. Symptoms resolve after a few weeks.

Diagnosis

Natural history and the presence of the above signs and symptoms suggest the diagnosis. For confirmation, some tests are used. One of them is edrophonium test, an anticholinesterase drug with short duration is applied intravenously; improvement of the muscle function suddenly and briefly confirms the diagnosis. Electrophysiological tests and serological abnormalities in the blood support the diagnosis. Repetitive stimulation test has a sensitivity of 60 percent and a technique called single fiber electromyography yields up to 95 percent. Acetylcholine receptor antibodies are found in the serum of 90 percent of patients with generalized disease, but only in 50 percet with the ocular form. Computed tomography (CT) of the mediastinum is also employed for a possible abnormality in the thymus gland.

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