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TECHNICAL CORNER: PERIODIC LIMB MOVEMENTS IN SLEEP
By Wayne Peacock, RPSGT
Question
What are periodic limb movements in sleep and how should
they be scored?
Answer
Excessive movement prior to or after sleep onset may severely affect the quality and quantity of an individual’s sleep and may lower
a patient’s sleep efficiency rating as measured by an overnight sleep
study. This article will take a closer look at the rules for scoring limb
movement that are outlined in the AASM scoring manual.1
Arousals caused by limb movements may lead to long periods of
wakefulness during polysomnography (PSG). The recording may
show delayed sleep onset latency, frequent arousal from sleep and
increased fragmentation of sleep architecture.2 Although this article
will focus on the scoring of periodic limb movements in sleep
(PLMS) that occur in the lower extremities, movements of the upper limbs may be recorded if clinically indicated.1
DEFINITIONS & SCORING
PLMS occur in 80 percent to 90 percent of patients with restless
legs syndrome (RLS), although RLS may be seen in only 30 percent of patients with PLMS. Both PLMS and RLS are classified
as sleep related movement disorders. RLS is estimated to affect
up to 10 percent of the population with an increasing prevalence
in older adults. It is a neurological condition that is characterized
by the irresistible urge to move the legs in the evening or at night.
Symptoms of RLS may impair the onset of sleep or the return to
sleep after an awakening.
About six percent of the general population and 45 percent of
adults aged 65 and older have PLMS, which are defined as repetitive limb movements during sleep that are stereotypically characterized by rhythmic movements of the big toe and a dorsiflexion of
the ankle.2 Episodes also may include movement in the knee and
hip. These movements may be seen in one or both lower extremities.
Movements of this nature are generally recorded with surface
electrodes placed longitudinally and symmetrically around the
middle of the anterior tibialis muscle so that they are 2 to 3 cm
apart or 1/3 of the length of the muscle, whichever is shorter.1 Both
legs should be monitored for the presence of limb movements,
and separate channels for each are strongly recommended by the
AASM. Combining the electrodes from the two legs to give one
recorded channel may suffice for some clinical settings, although
this strategy may reveal a reduced number of detected movements.
Leg movements (LMs) are scored per event, and a combination of
Wayne Peacock, RPSGT
Wayne Peacock, RPSGT, has been in the
sleep field for 10 years and is the manager of the Sleep Disorders Center and
Neurodiagnostic Department at Baptist
Hospital in Pensacola, Fla.
movements will define an episode of PLMS.
The AASM scoring manual defines a significant LM as a movement with a minimum duration of 0.5 seconds and a maximum
duration of 10 seconds. The movement also has an amplitude criterion of a minimum of 8uV increase in EMG activity from resting
EMG. LM onset is defined as the point at which there is an 8uV
increase in EMG voltage above resting EMG, and the ending of
the event is defined as the start of a period lasting 0.5 seconds during which the EMG does not exceed 2uV above resting EMG. To
score a PLMS sequence you should have at least 4 movements that
meet LM criteria and that occur at least 5 seconds but no more
than 90 seconds apart.1
According to the AASM scoring manual, the scoring technologist must use care to ensure that a LM is not scored if it occurs
during a period from 0.5 seconds preceding an apnea or hypopnea
to 0.5 seconds following a respiratory event.1 The scoring manual
also states, “An arousal and a PLM should be considered associated
with each other when there is <0.5 seconds between the end of one
event and the onset of the other event regardless of which is first.”1
HISTORY & REPORTING
During history taking the sleep technologist should document
any reported history of RLS or the symptoms associated with the
syndrome, as well as any abnormal movements during sleep that
are reported. The recording of limb movement activity during a
PSG should be evaluated in terms of the frequency and periodicity
of occurrence, along with the sleep stage in which this activity is
observed.3
The PLMS index is calculated by multiplying the number of
PLMS events by 60 and then dividing by the total sleep time
measured in minutes. The PLMS arousal index is calculated by
multiplying the number of PLMS events with arousal by 60 and
dividing by the total sleep time.1
A PLMS index below five events per hour is considered within
normal limits. An index of five to 25 is classified as mild, 25 to 50 is
moderate and an index greater than 50 is considered severe.2
CONCLUSION
PLMS, which is common in people with RLS, may be associated with a severe disruption to sleeping patterns by contributing to
problems in achieving and maintaining sleep. Precise scoring and
reporting of these events during PSG is necessary for the accurate
diagnosis of the patient’s sleep disorder.
References
1. American Academy of Sleep Medicine. The AASM
manual for the scoring of sleep and associated events: rules,
terminology and technical specifications. Westchester, Ill:
American Academy of Sleep Medicine; 2007. p. 18, 41.
2. Chokroverty S, Bhatt M. Motor events. In: Butkov N,
Lee-Chiong T, editors. Fundamentals of sleep technology.
Philadelphia: Lippincot Williams & Wilkins; 2007. p.371.
3. American Association of Sleep Technologists Technical
Guideline for Standard Polysomnography: Update 3-2008.
Available online to AAST members at www.aastweb.org.
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Figure 1. A 60-second excerpt in stage N2 sleep from a therapeutic study of a 31-year-old with confirmed obstructive
sleep apnea. The study demonstrated a successful continuous positive airway pressure (CPAP) titration and noted a
significant increase in Leg movements after therapeutic pressure was achieved resulting in a diagnosis of periodic limb
movement disorder with a PLM index of 24.8. This example also shows a limb movement-associated arousal.
Figure 2. A 240-second excerpt from the PSG of a 54-year-old male who is on bilevel PAP therapy. This example
demonstrates a PLM event as well as a LM with arousal.
A2Zzz 18.2 | June 2009