Undiagnosed Sleep Apnea in MG Could Lead To Overmedication

A Canadian research group has found that a type of disturbed breathing during sleep resulting from obstruction of the airway is probably much more common in people with myasthenia gravis (MG) than it is in the general population. They say the problem, known as “obstructive sleep apnea” (OSA), may not always be correctly identified.

Michael Nicolle of the London Health Sciences Centre in Ontario and colleagues, who published their findings in the July 11 issue of Neurology, randomly selected 100 people with MG from 400 clinic patients and assessed their risk of obstructive sleep apnea.

Fifty were identified as high-risk, and 37 agreed to undergo sleep studies. Of those, 34 were found to have OSA, mostly due to weakness of the mouth and throat muscles rather than the respiratory diaphragm. Most experienced episodes of abnormally slow, shallow breathing. Two people in the low-risk group were also found to have sleep apnea, yielding a total of 36 out of 100 (36 percent) MG patients in this study with this condition.

The prevalence of OSA in the general population is estimated at 15 percent to 20 percent, so the MG patients showed a much higher than average rate of this condition. In fact, the researchers say, they believe 36 percent is an underestimate, since 13 of the high-risk patients didn’t have sleep studies.

Sleep apnea can lead to sleep deprivation and significant daytime fatigue, which could be misinterpreted as resulting from overall worsening of the patient’s MG, the authors say. They caution, “Without considering a role for OSA, a history of fatigue could lead to deleterious increases in corticosteroids.” The correct treatment for obstructive sleep apnea is usually delivery of pressurized air by mask.