How is extraocular muscle weakness characterized in patients with myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Typically, extraocular muscle weakness is asymmetric. The weakness usually affects more than 1 extraocular muscle and is not limited to muscles innervated by a single cranial nerve; this is an important diagnostic clue. The weakness of lateral and medial recti (more commonly involved) may produce a pseudointernuclear ophthalmoplegia, described as limited adduction of 1 eye, with nystagmus of the abducting contralateral eye on attempted lateral gaze. Pupillary responses are normal. Cogan’s lid twitch describes a brief momentary twitch seen in an eyelid that is elevated on rest. Following sustained downgaze the patient is asked to bring the eyes back up to the primary gaze position. The upper eyelid briefly overshoots resulting in exposure of the sclera between the upper limbus and upper eyelid, followed by a rapid drop to a lower position and return of ptosis of the eyelid. The “twitch” is the momentary elevation of the eyelid before it drops due to fatigue of the levator palpebrae superioris muscle. This sign is not unique to MG and may be seen in dorsal brain stem glioma and menigioma.


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