Ocular Myasthenia - Signs and Symptoms

Signs and Symptoms

Although these blocking antibodies may be confined to one of the larger muscles responsible for moving the face or appendages or for breathing, about 90% of MG patients eventually have eye involvement. The most common symptoms are double vision (diplopia) and eyelid drooping (ptosis), whereas the pupil is always spared. Diplopia occurs when MG affects a single extraocular muscle in one eye, limiting eye movement and leading to double vision when the eye is turned toward the affected muscle. Ptosis occurs when the levator palpebrae superioris (the muscle responsible for eyelid elevation) is affected on one or both sides, leading to eyelid drooping. Although these symptoms may not be readily apparent in well-rested patients, weakness can usually be induced with exercise of the commonly affected muscles (e.g. by having the patient look upward for about 60 seconds).

In 75% of MG cases, the initial manifestation is in the eye. Within 2 years, 80% of patients with ocular onset of MG will progress to involve other muscle groups, thereby developing generalized MG. If MG is confined to the ocular muscles for more than 3 years, there is a 94% likelihood that the symptoms will not worsen or generalize.

Aside from asymmetric ptosis (which becomes worse with fatigue, sustained upgaze, and at the end of the day) and variable limitation of extraocular muscles/diplopia, other clinical signs of ocular MG include gaze-evoked nystagmus (rapid, involuntary, oscillatory motion of the eyeball) and Cogan’s lid twitch (upper lid twitch present when patient looks straight ahead after looking down for 10–15 seconds).