Sleep Disorders in Multiple Sclerosis
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.
Sleep Scheduling Disorders can be seen in shift workers, as a result of jet lag or frequent time zone change, in the old or in teenagers. Obviously, MS patients are as vulnerable as any other group to these kinds of problems. However, since an MS lesion could involve the hypothalamic region of the brain, which is involved in the sleep-wake cycle, a heightened concern for an MS plaque in a strategic site broadens the MS differential diagnosis for a Sleep Schedule Disorder.
These days there's a lot of TV time for Restless Leg Syndrome. This can be associated with the Parasomnia of Nocturnal Myoclonus or leg jerking during sleep. Periodic Leg Movements (PLM) can interrupt sleep and cause EDS. A sleep study can detect their presence. Gomez-Choco et. al from Spain in 2007 found that RLS in MS is not more frequent than in the general population. Again, any MS patient with leg jerking deserves a Brain MRI to hunt for an MS lesion in the brain stem that might be the initiating factor.
Other Parasomnias such as Night Terrors are typically seen in children and are outgrown. Sleep Walking and Sleep Talking are rarely serious medical conditions. REM Sleep Behavior Disorder (RBD) has been described for a few decades, particularly in men over 70. It is characterized by the acting out of violent dreams, sometimes placing the bed partner in some danger. It is due to shrinkage of the brain stem, which is involved in REM sleep. In MS, although there is no widespread reporting of RBD, a few cases have been cited where RBD occurs in younger patients with corresponding MS lesions in the brain stem. In 2002, Plazzi from Italy described RBD as the initial sign of MS in a 25-year-old woman.