[Respiratory disorders during sleep and myasthenia]

A sleep apnea syndrome is described by several studies in patients with myasthenia gravis. Apnea and hypopnea are mainly not obstructive and occur predominantly in rapid eye movement (REM) sleep. They are associated with oxygen desaturation. Although the sleep apnea index is not correlated with myasthenia gravis severity, it becomes less important as myasthenia gravis improves. Risk factors for the development of sleep apnea in myasthenia gravis patients are age, restrictive pulmonary syndrome, diaphragmatic weakness and daytime alveolar hypoventilation. Sleep apnea are not related to a central cholinergic effect in myasthenia gravis caused either by anticholinesterase used to treat myasthenia gravis or by antibodies to muscle acetylcholine receptors. Indeed acetylcholine receptors in brain are antigenically distinct from acetylcholine receptors in skeletal muscle. Sleep apneas are more likely caused by peripheral mechanisms. Correlation between sleep apnea and total lung capacity as well as the importance of diaphragmatic weakness in myasthenic patients may explain their predominance in REM sleep and their reduction with clinical improvement in the myasthenia gravis.