In general, Sleep Disorders are divided into conditions associated with Hypersomnia or Excessive Daytime Sleepiness (EDS), Disorders involving Difficulty in Initiating or Maintaining Sleep, Sleep Scheduling Disorders and Parasomnias or odd problems that co-exist with the sleep state.

Multiple Sclerosis (MS) is well represented in the Sleep Disorders department. To reiterate a point from the last article, one must distinguish between sleepiness and fatigue. There are questionnaire derived rating scales for both sleepiness and fatigue. In addition, EDS can be determined via a Multiple Sleep Latency Test (MSLT) wherein the patient is monitored for the time required to fall asleep during serial nap opportunities. But as I imply above, a Sleep Disorder need not involve either sleepiness or fatigue.

Major causes of the Hypersomnias are Obstructive Sleep Apnea (OSA), Central Sleep Apnea (CSA) (apnea meaning breathing pause) and Narcolepsy. All of these can be operative in Multiple Sclerosis, the most common being OSA which is the leading cause of Excessive Daytime Sleepiness in the vast majority of people with or without a concurrent disease. Sometimes, incoordination in breathing, which is more common in MS than in those without it, can worsen the upper airway obstruction. The latter is the major cause of OSA. Features include large tonsils, a narrow air space in the back of the mouth (often a normal variation) and/or neck obesity. Snoring is often present; men are more often affected. In MS, the central control of breathing can be impaired due to plaques in the brain stem. This can cause Central Sleep Apnea. MS patients, like many others can have combinations of OSA and CSA when tested in an overnight Polysomnogram (PSG) at a sleep center. The Hypersomnia is caused as a result of the night’s sleep being of poor quality due to frequent apneas, i.e. breathing stoppages. 

Narcolepsy on the other hand is not a sleep-breathing disturbance. It is related to a deficiency in the neurohormone hypocretin, usually on a genetic basis. This fragments dream or Rapid Eye Movement (REM) sleep leading to EDS, as the patient will have attacks of sleep, often with unplanned REM naps during the day. The Narcolepsy patient may also have dream hallucinations on falling off to sleep or upon awakening. He or she can also have Cataplexy, which is a sudden loss of muscle tone usually in response to emotional stimulation. Some case reports have described Narcolepsy or Narcolepsy-like illness in patients with MS. However Frauscher et. al. in 2005 in a report from Austria found no evidence for overall increased daytime sleepiness in MS patients compared to healthy controls.

MS patients have pain, depression and anxiety all of which can cause Insomnia, i.e. Disorders Initiating or Maintaining Sleep. However, most Insomnia is Psychophysiological- that is related to a pattern of sleep difficulties that is not specifically due to a physical trigger or a recurrent identifiable rumination. This is true in MS as well. It should be noted however that the Apneas can also cause Insomnia. Many would argue that an MS patient, because of that concern about a Central Apnea component inducing Insomnia, should have a PSG even if there is no classic loud snoring history or Excessive Daytime Sleepiness.