The fatigue felt by most multiple sclerosis (MS) patients could be caused by an undiagnosed sleep disorder rather than the MS itself. New research from the University of Michigan suggests that MS patients are at a high risk for a disorder called obstructive sleep apnea (OSA) — a treatable condition.

Patients with MS — a neurological disease that damages the brain, spinal cord, and optic nerves — can experience paralysis in their limbs, difficulty speaking, and a gradual loss of vision, among other symptoms. Chronic fatigue, or more simply described as an unending tiredness, makes up one of its most debilitating symptoms. According to the National Multiple Sclerosis Society, the cause of fatigue in MS currently remains unknown. Some patients struggle when their fatigue is misinterpreted as depression, apathy, or a lack of interest at their workplaces and in their social lives.

Researchers previously believed that patient’s fatigue was caused entirely by MS. But the new research suggests that because MS patients may be more likely to have sleeping disorders (even undiagnosed ones), their fatigue could be caused from — and often worsened by — their lack of sleep.

The study’s lead author, Tiffany Braley, said in a news release that "the findings should prompt doctors who treat MS patients to consider sleep apnea as a possible contributor to their patients' fatigue, and recommend appropriate testing and treatment." Nevertheless, Braley also warns that the study doesn’t set down any solid cause-and-effect theories between fatigue and OSA.

In their analysis of 195 patients at the University of Michigan Multiple Sclerosis Center, Braley’s team used questionnaires and medical records to assess sleep health. All test patients had been diagnosed with MS for an average of 10 years.

They found that though most of the patients had never been formally diagnosed with a sleeping disorder, 56 percent of the patients were at an increased risk for OSA. Furthermore, the patients with the highest risk also reported themselves to be the most tired. The research team made sure no external factors like age, gender, or mental illnesses were contributing to the fatigue.

According to Braley, the importance of the findings lies in the fact that “OSA may be a highly prevalent and yet under-recognized contributor to fatigue in persons with MS."

Doctors routinely treat OSA with continuous positive airway pressure (CPAP). During CPAP treatment, patients put on a mask attached to a machine in order to receive a steady stream of air into their nostrils and mouth. This helps keep the patient’s airways open, since during sleep apnea these airways are blocked. Blocked airways can contribute to difficult breathing during sleep.

Source: Braley TJ, Segal BM, Chervin RD. Obstructive sleep apnea and fatigue in patients with multiple sclerosis. Journal of Clinical Sleep Medicine. 2014.