Periodic limb movement disorder (PLMD) and restless
leg syndrome (RLS) are distinct disorders, but often
occur simultaneously. Both PLMD and RLS are also called
(nocturnal) myoclonus, which describes frequent or
involuntary muscle spasms. Periodic limb movement was
formally described first in the 1950s, and, by the
1970s, it was listed as a potential cause of insomnia.
In addition to producing similar symptoms, PLMD and RLS
are treated similarly.
PERIODIC LIMB MOVEMENT DISORDER
Periodic limb movement disorder affects people only
during sleep. The condition is characterized by behavior
ranging from shallow, continual movement of the ankle or
toes, to wild and strenuous kicking and flailing of the
legs and arms. Furthermore, abdominal, oral, and nasal
movement sometimes accompanies PLMD. Movement of the
legs is more typical than movement of the arms in cases
of PLMD. Movements typically occur for 0.5 to 10
seconds, in intervals separated by five to 90 seconds.
In 1979, the Association of Sleep Disorder Centers (ASDC)
set the parameters for determining the presence of PLMD:
- A formal diagnosis of nocturnal myoclonus
requires three periods during the night, lasting
from a few minutes to an hour or more, each
containing at least 30 movements followed by partial
arousal or awakening. (ASDC 1979)
Today, these parameters are a bit more relaxed, and
PLMD usually includes any repetitive, involuntary
movement during the night. These limb movements usually
occur in deep stage two sleep, but often cause arousal.
Thus, PLMD can cause poor sleep, which may lead to sleep
maintenance insomnia and/or excessive daytime
sleepiness.
The incidence of PLMD increases with age. It is
estimated to occur in 5% of people age 30 to 50 and in
44% of people over the age of 65. As many as 12.2% of
patients suffering from insomnia and 3.5% of patients
suffering from excessive daytime sleepiness may
experience PLMD.
RESTLESS LEG SYNDROME
Restless leg syndrome was described as early as the
16th century but was not studied until the 1940s. People
with RLS complain of an irresistible urge to move their
legs while at rest. A person with RLS will experience a
vague, uncomfortable feeling while at rest that is only
relieved by moving the legs. The symptoms of RLS may be
present all day long, making it difficult for an
individual to sit motionless. On the other hand, they
may be present only in the late evening. Late evening
symptoms can lead to sleep onset insomnia, which tends
to compound the effects of RLS. Pregnancy, uremia, and
post-surgery conditions have also been known to increase
the incidence of RLS. In addition, surprisingly, fever
seems to decrease it.
Although one study found RLS to be most prevalent in
middle-aged females, its incidence increases with age.
Restless leg syndrome is estimated to affect 5% of
the population. Approximately 80% of people with RLS
have PLMD, though most people with PLMD do not
experience RLS.
SYMPTOMS OF PERIODIC LIMB MOVEMENT DISORDER
People with PLMD may be completely asymptomatic, or
they may complain of either excessive daytime sleepiness
or insomnia, or both. Limb movements can be severe
enough to wake an individual from sleep, making it
difficult to stay asleep for a significant duration and
leading to excessive daytime sleepiness. Many patients
who suffer from excessive daytime sleepiness do not know
they are being aroused from sleep by periodic limb
movements because they do not actually wake up. Rather,
they will feel as though they have not slept well. These
arousals can occur anywhere from five times an hour up
to more than 50 times an hour, depending on the severity
of movement.
As mentioned earlier, leg movements in PLMD are
typically an upwardly flexed big toe and ankle.
Sometimes the hip and knee are flexed and tightened as
well.
Because periodic limb movements have been observed in
patients with healthy sleep patterns, the claim that
they predicate a higher incidence of sleep disorder is
controversial. Some studies have shown no greater
occurrence of PLMD in patients with insomnia than in
those with sleep-wake conditions like excessive daytime
sleepiness.
SYMPTOMS OF RESTLESS LEG SYNDROME
People with RLS find it difficult to keep their legs
still and must move them to alleviate the discomfort.
The feeling is usually difficult for them to articulate
because it is less of a throbbing or stabbing pain and
more of a nonspecific discomfort. Many who experience
RLS also experience generalized anxiety that results
from the incessant need to change the positioning of
their legs. Moving the legs temporarily relieves the
discomfort.
The intensity of RLS can vary significantly
throughout the day. Many people have no symptoms at all
until nighttime, when they attempt to sleep. The
discomfort in the legs and the need to move them
prevents them from sleeping. Other patients have severe
symptoms all day long, which may affect work, travel, or
the ability to concentrate.
CAUSES
The causes of PLMD and RLS are unknown. The vast
majority of PLMD and RLS cases occur independently of
other disease processes. It is certain that these
conditions often cause insomnia, and some research shows
that they might also be caused by other sleep
disturbances. This is not likely, however, as PLMD and
RLS have not been found to a significant degree in most
cases of sleep apnea, which seems to precipitate many
secondary consequences of sleep disturbance.
There are many conditions that have been associated
with PLMD and RLS, including:
- Chronic renal failure
- Myelopathies (conditions of the spinal cord)
- Peripheral neuropathies
- Amyloidosis (metabolic disorder of organs and
tissues)
- Diabetes mellitus
- Anemia and related hemoglobin deficiencies
- Iron deficiency
- Vitamin B12 deficiency
- Uremia (kidney-related toxicity)
- Chronic lung disease
- Leukemia
- Rheumatoid arthritis
- Fibromyalgia
- Stiff-man syndrome
- Isaac’s syndrome
- Huntington’s chorea
- Amyotrophic lateral sclerosis (ALS)
Certain medications may also induce RLS and PLMD,
including lithium and tricyclic antidepressants.
Withdrawal from other medications, including
anticonvulsants, benzodiazepines, and barbiturates may
also induce RLS and PLMD.
PLMD
A sleep partner may observe the occurrence of
periodic limb movements, which often affect the partner
before the patient knows of his or her behavior. In
other cases, however, the diagnosis is made by a sleep
technician during an overnight polysomnogram, which
records sleep and the bioelectrical processes that
govern it. This test is often used to assess the cause
of excessive daytime sleepiness, such as PLMD and
obstructive sleep apnea.
RLS
The diagnosis of RLS is based on the patient’s
description and personal history of his or her
affliction. Because it presents no external secondary
symptoms, RLS can be difficult to identify. There are
studies designed to quantify the effects of RLS, though
these are used mostly for research purposes. For
example, a Suggested Immobilization Test, or Forced
Immobilization Test, is performed while the patient
either voluntarily keeps his or her legs motionless or
while the legs are immobilized with a stretcher. The
limb movements are then monitored with an EMG. In both
PLMD and RLS, a complete examination to exclude
secondary causes is warranted.
Furthermore, it is necessary to distinguish PLMD from
other more serious types of nocturnal movement, such as
seizure. Nocturnal seizures present problems for
patients because they can cause injury and are
indicative of disorders that require specialized
treatment. In addition, iron and calcium deficiencies
often produce symptoms that mirror RLS, such as leg
cramping and tenderness.
TREATMENT
Generally, there are three classes of drugs that are
used to treat PLMD and RLS. These are benzodiazepines,
Parkinson drugs, and narcotics. Medical treatment of
PLMD and RLS often significantly reduces or eliminates
the symptoms of these disorders, though not always.
There is no cure for PLMD or RLS, and medical treatment
must be continued to provide potential relief.
Clonazepam is the most commonly employed
benzodiazepine treatment. It is effective in many cases,
but not all, and it usually causes drowsiness or
sedation. Sometimes, clonazepam allows the patient a
better, more restful night’s sleep without affecting the
occurrence of limb movement. Patients with PLMD may have
other sleep disorders, such as obstructive sleep apnea,
which the use of clonazepam could worsen.
The drugs used to treat Parkinson’s disease are also
very effective against PLMD and RLS. These include,
L-dopa/carbidopa, bromocriptine (which suppresses the
excretion of prolactin), pergolide, and selegiline. If
either benzodiazepines or Parkinson’s medications do not
relieve symptoms, then narcotics, such as codeine,
oxycodone, methadone, and propoxyphene are sometimes
employed.
