What history is characteristic of myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas A Jowkar, MBBS; Chief Editor: Nicholas Lorenzo, MD, CPE, MHCM, FAAPL  more...
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Patients with myasthenia gravis (MG) present with painless, specific muscle weakness, and not generalized fatigue. Myasthenic weakness typically affects the extraocular, bulbar, or proximal limb muscles. Droopy eyelids or double vision is the most common symptom at initial presentation of MG, with more than 75% of patients. These symptoms progress from mild to more severe disease over weeks to months. Difficulty in swallowing, slurred or nasal speech, difficulty chewing, and facial, neck, and extremity weakness occur. [32] On the other hand, symptoms may remain limited to the extraocular and eyelid muscles for years. Rarely, patients with severe, generalized weakness may not have associated ocular muscle weakness.

The hallmark of MG is that muscles get weaker with repeated use. The examiner needs to establish this on the history and exam. It is important to discriminate fatigable weakness from nonspecific fatigue or somnolence. The prevalence of obstructive sleep apnea or poor sleep hygiene is higher in patients with MG; therefore, somnolence secondary to a sleep disorder may coexist with MG. [30] Psychosocial factors become important in assessment if a mood disorder or depression is suspected. Patients with fluctuating fatigable muscle weakness due to MG will describe weakness of a specific group of muscles that is brought on by activity and which improves with rest. In contrast, patients with generalized fatigue or exhaustion due to any number of causes will typically report generalized weakness, tiredness, or lack of energy. In myasthenia, often the complaint of weakness may be noted following exertion or at the end of the day. This often results in little detectable objective weakness at the time of examination. Maneuvers that fatigue specific muscle groups can be very useful in provoking weakness in patients. In contrast, patients with generalized fatigue or malaise do not typically display true muscle weakness with provocative maneuvers.

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