Which clinical history findings are characteristic of myasthenia gravis?

Updated: Sep 20, 2018
  • Author: William D Goldenberg, MD; Chief Editor: Andrew K Chang, MD, MS  more...
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Thyroid disorders may be seen in as many as 10% of patients with myasthenia gravis, and symptoms of hyperthyroidism or hypothyroidism may be present.

Rarely does a patient present with undiagnosed myasthenia gravis. However, if this situation does occur, typical complaints are of generalized weakness and reduced exercise tolerance that improves with rest. [5] Patients with myasthenia gravis do not present with primary complaints of sleepiness or muscle pain. The patient may also complain of a specific weakness of certain muscle groups (eg, those used when climbing stairs).

The distribution of muscle weakness follows a characteristic pattern; initially 85% of patients have involvement of the eyelids and extraocular muscles, resulting in ptosis and/or diplopia. [1] The involvement of the facial muscles results in changes in expression and speech, whereas involvement of the pharyngeal muscles results in progressive difficulty with mastication and deglutition.

In 15-20% of patients, myasthenia gravis affects the bulbar muscles alone. The other patients progress to generalized myasthenia gravis. [1]

Neck and proximal limb weakness may occur. Eighty percent of patients with bulbar weakness go on to develop generalized weakness involving the limbs. [3] Respiratory weakness may be present. Respiratory failure occurs in 1% of patients.

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