Walsh & Hoyt: Disturbances in Disorders of the Neuromuscular Junction

Myasthenia gravis (MG) is an autoimmune disorder characterized by pathogenic antibodies against acetylcholine receptors at motor terminals. Clinically apparent weakness of the intraocular muscles is rare. Nonetheless, abnormalities of pupillary function and accommodation are occasionally reported in patients with MG. Two patients with anisocoria and sluggish pupil light reflexes that resolved following treatment with cholinesterase inhibitor have been described. Pupillary fatigue during prolonged light stimulation has also been noted in other patients. Yamazaki and Ishikawa used an open-loop stimulus and infrared video pupillography to record direct pupillary responses to light as well as their velocities and acceleration in seven patients with MG and in three healthy persons. Their results suggest that involvement of the iris sphincter is common in patients with MG. Lepore et al. reported abnormalities of pupil cycle time, but most of these patients were taking anticholinesterase agents, systemic corticosteroids, or both, which may have affected their pupillary movements. In addition, it is not clear whether the pupillary abnormalities observed were caused by direct involvement of the iris musculature, the neuromuscular junction, or central pathways of the pupillary light reflex. Bryant concluded that patients with severe MG tend to show significant interocular differences in pupil cycle times, with the degree of difference correlating with the severity of the illness. Botulism. Lambert-Eaton myasthenic syndrome.