Results from a study conducted in Australia show that a nighttime respiratory problem called obstructive sleep apnea occurs more frequently in people with Friedreich's ataxia (FA) than in the general population.
Obstructive sleep apnea is a disorder in which the muscles of the throat intermittently relax and block the upper airway during sleep, causing pauses in breathing. This can lead to a reduction in the amount of oxygen that makes it to vital organs and to irregular heart rhythms.
In people with FA who participated in the study, the presence of obstructive sleep apnea was significantly correlated with having had the disease for a longer period of time and with more severe symptoms.
In a paper published online May 22, 2013, in Neurology, Louise Corben at Murdoch Children's Research Institute in Parkville, Australia, and colleagues, recommend that people with FA undergo regular screening for obstructive sleep apnea to identify the need for further study and possible subsequent treatment.
The investigators administered the Epworth Sleepiness Scale (used to evaluate how sleepy someone is during the day) once a year, for up to three years, to 82 people, ages 10 to 71 years, with a genetically confirmed diagnosis of FA. They referred those who scored greater than 8 on the scale, or who showed clinical symptoms suggestive of a nighttime respiratory disorder, to have a polysomnogram, an assessment designed to pinpoint the causes of fragmented or disrupted sleep via a combination of measurements, including encephalographic (brain) activity, eye movement, muscle activity, heart rhythm, respiratory effort, nasal and oral airflow, oxygen saturation, carbon dioxide levels, limb movements and snoring.
Out of 82 people with FA in the study, 17 (21 percent) received a diagnosis of obstructive sleep apnea. In nine participants, it was classified as mild; in three, moderate; and in five, severe. By contrast, the investigators estimate the prevalence of obstructive sleep apnea in the general population to be between 3 and 7 percent.
The risk of developing obstructive sleep apnea for those in the study was 5.1 times higher than for those in the general population.
Importantly, although body mass index is significantly correlated with obstructive sleep apnea in the general population, there was no correlation detected between the two in people with FA.
In addition, the presence of obstructive sleep apnea was significantly correlated with the duration of disease and clinical severity: Participants who received a diagnosis of obstructive sleep apnea had longer disease duration and more severe disease than those who did not.
FA can cause a reduction in the ability to control the bulbar muscles, which may explain the correlation between longer disease duration and the presence of obstructive sleep apnea. However, because there was no objective measure of bulbar function, it can't be determined whether this was the cause of the disorder in people who participated in the Australian study.
Other characteristics of FA that may contribute to development of obstructive sleep apnea include reduced respiratory muscle strength, scoliosis and poor posture.
The researchers note that an association exists between obstructive sleep apnea and fatigue — a symptom that frequently is reported by people with FA in quality of life studies. The mechanism that underlies FA-related fatigue is not known, but obstructive sleep apnea may play a role.
In addition, it's possible that obstructive sleep apnea in people with FA may:
The investigators note that the study data support routine screening for evidence of nighttime respiratory problems in people with FA, and subsequent treatment if obstructive sleep apnea or other breathing disorders are detected.
Note: Standard treatment of obstructive sleep apnea (continuous positive airway pressure, or CPAP) may not always be appropriate for people with neuromuscular disease. For more information, see Not Enough ZZZzzzs?