Introduction:

Restless legs syndrome (RLS) is an unsettling and poorly understood movement disorder affecting 3 - 15% of the general population. RLS can affect both children and adults. Although effective treatments are available, the condition often remains undiagnosed.

Symptoms of RLS. The core symptom of RLS is an irresistible urge to move the legs (medically known as akathisia). Some people describe this symptom as a sense of unease and weariness in the lower leg, which is aggravated by rest and relieved by movement. Specific characteristics of RLS include:

• "Pulling, searing, drawing, tingling, bubbling, or crawling" beneath the skin, usually in the calf area, causing an irresistible urge to move the legs. These sensations can occur not only in the lower legs, but they can also affect the thighs, feet, and even the upper body. RLS-type symptoms may also occur in the arms. This may be the first symptom of RLS in some people.
• About 80% of patients with RLS also experience semi-rhythmic movements called periodic limb movement disorder (PLMD).
• Itching and pain, particularly aching pain, may be present.
• Patients experience symptoms when they feel most relaxed and their legs are at rest. (Movement, however, brings relief.) Symptoms usually occur at night when lying down, or sometimes during the day while sitting.
• Episodes of RLS usually develop between 10 p.m. and 4 a.m. Symptoms are often most severe shortly after midnight. They typically occur for 30 - 60 seconds, and they usually resolve by morning. If the condition becomes more severe, people may begin to have symptoms during the day. These symptoms are always worse at night, however.
• At night, the unpleasant sensations and the resulting uncontrollable urge to move the legs can often disturb sleep. Ignoring the need to move the legs usually only builds up tension until they jerk uncontrollably. If patients experience symptoms during the day, they usually feel compelled to move their legs in order to relieve the symptoms, making it difficult to sit during air or car travel or through classes or meetings.

Late-onset and Early-onset Forms. There appear to be two forms of RLS, early-onset and late-onset. Each form may have different characteristics:

• People with early-onset RLS (occurring in the teenage years or earlier) tend to have a family history of the disorder. They also usually have RLS without accompanying pain.
• Those with late-onset RLS usually do not have a family history of RLS. Their condition is more likely the result of a problem with the nervous system, and symptoms may include pain in the lower legs.

Periodic Limb Movement Disorder

The medical term for periodic limb movement disorder (PLMD) is nocturnal myoclonus. PLMD symptoms include:

• Episodes that usually occur during the night, peaking near midnight, as they do in restless legs syndrome (RLS).
• Leg muscles 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 wake patients. PLMD is distinct from the brief and sudden movements that occur just as people are falling asleep, jolting them awake.

Although 80% of RLS sufferers have PLMD, only about 30% of people with PLMD also have RLS. While treatments for the two conditions are similar, PLMD is a separate syndrome. PLMD is also very common in narcolepsy, a sleep disorder that causes people to fall asleep suddenly and uncontrollably.

Nocturnal Leg Cramps

Cramps that awaken people during sleep are very common, and they are not part of restless legs syndrome or periodic limb movement disorder. 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. However, individual adults differ in the amount of sleep they need to feel well rested. Infants may sleep as many as 16 hours a day.

The daily cycle of life, which includes sleeping and waking, is called a circadian rhythm (circadian means "about a day"), or the biological clock. Hundreds of bodily functions follow biologic clocks, but sleeping and waking comprise the most prominent circadian rhythm. The sleeping and waking cycle is about 24 hours long. If confined to windowless apartments, with no clocks or other time cues, sleeping and waking only as their bodies dictate, humans typically live on slightly longer than 24-hour cycles.

The circadian rhythm usually takes the following daily patterns:

• Humans prefer daytime activity and nighttime rest.
• A natural peak in sleepiness occurs at mid-day, the traditional siesta time.
• Daily rhythms interact 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 changes in exposures to light and dark, can unsettle the pattern.

The Response in the Brain to Light Signals. The brain's response to light signals 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). This cluster is the body's master clock, which is called the supra chiasmatic nucleus (SCN). The SCN is named for its location, which is just above (supra) the optic chiasm, a major junction where nerves transmit 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 pinecone) to produce the hormone melatonin.
• Researchers think that melatonin acts as the body's time-setting hormone. It also appears to trigger the need to sleep. The longer a person is in darkness, the longer the duration of melatonin secretion. Staying in bright light can decrease the secretion of melatonin.

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. Non-rapid eye movement (NREM) sleep is also called quiet sleep. NREM is further subdivided into three stages of progression:

• Stage 1: Light sleep
• Stage 2: "True" sleep
• Stage 3 to 4: Deep "slow-wave" or delta sleep

With each ascending stage, awakening becomes more difficult. It is not clear what governs NREM sleep in the brain. A balance between certain hormones, particularly growth and stress hormones, may be important for deep sleep.

Rapid Eye-Movement Sleep. Rapid eye-movement (REM) sleep is also called active sleep. Most vivid dreams occur in REM sleep. Brain activity in REM sleep is comparable to that in waking, but the muscles are virtually paralyzed, possibly preventing people from acting out their dreams. Except for vital organs like the lungs and heart, the only muscles not paralyzed during REM sleep 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 and active sleep generally follows this pattern:

• After about 90 minutes of NREM sleep, eyes move rapidly behind closed lids, giving rise to REM sleep.
• As sleep progresses the NREM/REM cycle repeats.
• With each cycle, NREM 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 cycle.

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.