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Restless Legs Syndrome and Related Disorders - Introduction
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Late- and Early Onset Forms. Some experts now believe there are two forms of RLS, early- and late-onset, and that each has different characteristics:
- People with onset of RLS in adolescence or earlier tend to have a family history of the disorder and to have RLS without accompanying pain.
- Those with later onset tend not to have a family history of RLS. Their condition is more likely to have a neurologic basis and symptoms are more like to include pain in the lower extremities.
Periodic Limb Movement Disorder (PLMD)
Periodic limb movement disorder (PLMD) is also called nocturnal myoclonus. PLMD symptoms include:
- As with RLS, episodes usually occur during the night, peaking at around midnight.
- Leg muscles involuntarily and repetitively contract and jerk every 20 - 40 seconds during sleep. Such movements may last less than 1 second, or as long as 10 seconds.
- Unlike RLS, contractions in PLMD usually do not arouse patients.(PLMD is distinct from so-called hypnic jerks, which are brief and sudden movements that occur just as people are falling asleep and jolt them awake.)
Although 80% of RLS sufferers experience PLMD, only about 30% of people with PLMD also have RLS. Although the two conditions can be treated similarly, there are some differences. PLMD, then, is considered to be a separate syndrome. PLMD is also very common in narcolepsy, a sleep disorder that causes people to suddenly fall asleep.
Nocturnal Leg Cramps
Cramps that awaken people during sleep are very common. They can be very painful and may cause a person jump out of bed in the middle of the night. They typically affect a specific area of the calf or the sole of the foot.
Healthy Sleep
Circadian Rhythm
In sleep studies, subjects spend about one-third of their time asleep, suggesting that most people need about 8 hours of sleep each day. Individual adults differ in the amount of sleep they need to feel well rested, however. (Infants may sleep as many as 16 hours a day.)
The daily cycle of life, which includes sleeping and waking, is called a circadian (meaning "about a day") rhythm, and commonly referred to as the biologic clock. Hundreds of bodily functions follow biologic clocks, but sleeping and waking comprise the most prominent circadian rhythm. The sleeping and waking cycle is approximately 24 hours. (If confined to windowless apartments, with no clocks or other time cues, sleeping and waking as their bodies dictate, humans typically live on slightly longer than 24-hour cycles.) It usually takes the following daily patterns:
- Humans are designed for daytime activity and nighttime rest.
- There is a natural peak in sleepiness at mid-day, the traditional siesta time.
- Daily rhythms intermesh with other factors that may interfere or change individual patterns:
- The fraction-of-a-second-firing of nerve cells in the brain may be faster or slower in different individuals.
- The monthly menstrual cycle in women can shift the pattern.
- Light signals coming through the eyes reset the circadian cycles each day, so changes in season or various exposures to light and dark can unsettle the pattern. The importance of sunlight as a cue for circadian rhythms is dramatized by the problems experienced by people who are totally blind. They commonly have trouble sleeping and suffer other sleep rhythm disruptions.
The Response in the Brain to Light Signals
The response to light signals in the brain is an important key factor in sleep:
- Light signals travel to a tiny cluster of nerves in the hypothalamus in the center of the brain, the body's master clock, which is called the supra chiasmatic nucleus or SCN.
- This nerve cluster takes its name from its location, which is just above (supra) the optic chiasm, which is a major junction for nerves transmitting information about light from the eyes.
- The approach of dusk each day prompts the SCN to signal the nearby pineal gland (named so because it resembles a pine-cone) to produce the hormone melatonin.
- Melatonin is thought to act as the body's time-setting hormone. The longer a person is in darkness the longer the duration of melatonin secretion. Secretion can be diminished by staying in bright light. Melatonin also appears to trigger the need to sleep.
Sleep Cycles
Sleep consists of two distinct states that alternate in cycles and reflect differing levels of brain nerve cell activity:
Non-Rapid Eye Movement Sleep (NonREM). NonREM sleep is also termed quiet sleep. NonREM is further subdivided into three stages of progression:
- Stage 1 (light sleep)
- Stage 2 (so-called true sleep)
- Stage 3 to 4 (deep "slow-wave" or delta sleep)
With each descending stage, awakening becomes more difficult. It is not known what governs NonREM sleep in the brain. A balance between certain hormones, particularly growth and stress hormones, may be important for deep sleep.
Rapid Eye-Movement Sleep (REM). REM sleep is termed active sleep. Most vivid dreams occur in REM sleep. REM-sleep brain activity is comparable to that in waking, but the muscles are virtually paralyzed, possibly preventing people from acting out their dreams. In fact, except for vital organs like lungs and heart, the only muscles not paralyzed during REM are the eye muscles. REM sleep may be critical for learning and for day-to-day mood regulation. When people are sleep-deprived, their brains must work harder than when they are well rested.
The REM/NREM Cycle. The cycle between quiet (NREM) and active (REM) sleep generally follows this pattern:
- After about 90 minutes of NonREM sleep, eyes move rapidly behind closed lids, giving rise to REM sleep.
- As sleep progresses the NonREM/REM cycle repeats.
- With each cycle, NonREM sleep becomes progressively lighter, and REM sleep becomes progressively longer, lasting from a few minutes early in sleep to perhaps an hour at the end of the sleep episode.
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 The hypothalamus is a highly complex structure in the brain that regulates many important brain chemicals. Malfunction of this area of the brain may give rise to cluster headaches.
Review Date: 10/18/2006
Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of
Medicine, Harvard Medical School; Physician, Massachusetts General
Hospital
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