Sleep. 8(3):239-243
© 1985 Raven Press. New York
Relationship of Periodic Movements in Sleep
(Nocturnal Myoclonus) and the Babinski Sign
Robert C. Smith
Sleep Disorders Center. St. Louis University. St. Louis, Missouri, USA
Summary: To obtain a comprehensive clinical description of periodic movements
in sleep, the first 11 videotaped movements of nine patients were studied. These
leg movements were characterized by active dorsiflexion of the ankle (91%),
dorsiflexion and fanning of the small toes (82%), and dorsiflexion of the great toe
(72%). Partial flexion of the knee and hip occurred in 28%. Simultaneous dorsiflexion of the ankle and small toe was almost always the initial change, either
preceding or occurring simultaneously with extension of the great toe. Knee and
hip flexion almost always followed foot movements. Tonic and/or clonic movements, usually about the ankle, occurred in 75%; plantar flexion of the ankle
occurred in 21% at the end of a leg movement. Periodic movements in sleep were
thus characterized on detailed videographic analysis by movements similar to the
Babinski response. Since both the normally occurring nocturnal Babinski response
and periodic movements in sleep are also almost entirely NREM related, the
author proposes that periodic movements in sleep are due to the NREM loss of
supraspinal inhibitory influences on the pyramidal tract and that the characteristic
foot and leg movements are Babinski-type responses secondary to this. Key
Words: Periodic movements in sleep-Nocturnal myoclonus-Babinski signPyramidal tract disease.
Current definitions of periodic movements in sleep (PMS) specify that the leg movements are characterized by rapid partial dorsiflexion of the ankle, extension of the great
toe, and partial flexion of the knee and hip (1,2). Although common, PMS is of uncertain
origin and significance (3) and has been reported in association with many different sleep
disorders and asymptomatic states (2,4). Although careful clinical observations of PMS
have been reported, including cinematographic analyses 0), the major emphasis has been
on the polysomnographic characteristics of these foot and leg movements (5). The present
study used videographic techniques in nine patients with PMS to make detailed observations
of their foot and leg movements. The findings corroborated, and slightly expanded, earlier
clinical descriptions and led to the hypothesis that periodic movements in sleep are Babinskitype responses due to changes in the pyramidal tracts during NREM sleep.
Accepted for publication May 1985.
Address correspondence and reprint requests to R. C. Smith at Division of General Internal Medicine, Department of Medicine, Michigan State University College of Human Medicine, East Lansing, MI 48824, U.S.A.
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R. C. SMITH
METHODS
Eight of the subjects were referred to the St. Louis University Sleep Disorders Center
with the following primary sleep complaints: insomnia (n = 3), snoring (n = 2), and
possible obstructive apnea (n = 3). One subject was a volunteer student. The evaluation
of each patient consisted of a medical and sleep history and a physical examination. Each
had a nocturnal polysomnogram which included the central (C3) and occipital (01) electroepcephalograms, electro-oculogram, submental electromyograms (EMG), and bilateral
anterior tibial EMGs. Some also had nasal/oral airflow recorded with a thermistor. Sleep
stages were scored according to the guidelines of Rechtschaffen and Kales (6). Videographic
study, performed with a video camera in the patient's room, was controlled by a technician
in an adjoining room to avoid disturbing the patient. Evaluation of the videotapes, at slow
and normal speeds, was performed by the author to rate the nocturnal movements of the
single foot and leg that could be captured on the videotape.
RESULTS
Nine Caucasian patients, six men and three women, mean age 41 years (range 21-67
years), were studied. The 9 subjects represented all patients suspected of having PMS for
whom adequate videotaping of the nocturnal leg movements could be obtained during a 6month period. Eight of the patients met Association of Sleep Disorders Centers' criteria
for nocturnal myoclonus while one patient had only two trains of myoclonus. There was
suspicion of nocturnal myoclonus in three patients and restless legs in five. Nocturnal
myoclonus was the primary diagnosis for the sleep disorder in four, a contributing factor
in two, and non-contributory in three patients. Other primary sleep-related diagnoses were
sleep apnea, insufficient sleep, and underlying medical conditions, i.e., one patient had
undergone craniotomy and had, on neurologic examination, only a visual field defect;
another patient had incurred a brain stem stroke resulting in isolated right-sided Horner's
syndrome. The remaining seven patients had no neurologic disease nor abnormalities on
physical examination.
Only the first 11 movements, all from NREM, in each of the nine cases were rated (range
11-27 movements, mean 17.3). Although there was considerable variability within and
among patients some common features of the periodic leg movements were observed. The
great toe was actively dorsiflexed in only 72 of 99 periodic leg movements (range per case
3-11) evaluated, while the ankle actively dorsiflexed in 91 of 99 movements (range per
case 3-11). Active dorsiflexion (with fanning) of the four small toes occurred in 82 of 99
movements, almost always simultaneously with ankle movement. Flexion of the knee and
hip occurred in only 28 of 99 movements (range per case 0-11), with no motion at all in
five cases. The sequence of foot movements showed three common patterns: ankle and
small toe movement alone (32 of 99 movements); ankle and small toe movement followed
by great toe movement (27 of 99 movements); ankle, small toe, and great toe movement
simultaneously (27 of 99 movements). The great toe preceded the ankle and small toes in
only 2 of 99 movements. Movement of the ankle alone (2 of 99 movements), great toe and
ankle (1 of 99 movements), and knees and hips alone (8 of 99 movements) accounted for
the remainder. When movement of the knees and hips was associated with foot movement
(20 of 99 movements), it followed in 18 of 20 movements and preceded in 2 of 20 movements. Repetitive up-down (clonic) foot movements, usually represented on EMG as typical
single leg movements, were the rule; only 1 of 9 cases showed no clonus. There was a total
of 55 of 99 repetitive movements. The mean number of repetitions was 2.8, involving the
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ankle in 7 of 8 cases and the great toe in 1 of 8 cases. Tonic movements, defined as either
sustained dorsiflexion or delay in relaxation following dorsiflexion, occurred in 34 of 99
movements, involving the ankle and small toes in 6 of 7 cases and the great toe in 1 of 7
cases. Twenty of 34 tonic movements occurred where there had been no clonic movements,
so that a total of 75 of 99, including all patients, exhibited tonic and/or clonic foot movements. Plantar flexion occurred in 21 of 99 movements at the end of the foot movements.
Of the five cases exhibiting this, four occurred with the ankle and small toes and one
involved the great toe.
DISCUSSION
An active tonic/clonic dorsiflexion of the ankle and toes best describes the periodic
movements of sleep reported here, while flexion of the knees and hips was much less
prominent. Dorsiflexion of the ankle and small toes was almost always the initial movement,
at times accompanied by dorsiflexion of the great toe. There were important limitations to
the study, however. A larger population and independent rating would have enhanced the
findings. Direct electrophysiological confirmation of the many observed movements (from
the extensor halluc is longus, flexor halluc is brevis, tibialis anterior, and extensor digitorum
longus, for instance), although difficult to obtain because of their invasive nature, would
have been useful in verifying the number and sequence of these rapid foot movements.
Study of patients at different times of night, on different nights, and of both legs will be
important in future studies. Nevertheless, the study was consistent with descriptions by
both Guilleminault (1) and Coleman (2). Lugaresi (7) also emphasized clonic activity in
conjunction with what he defined as the closely related restless legs syndrome.
The author was intrigued by the similarity of these foot and leg movements to the abnormal
plantar response (Babinski sign) that is elicited by stroking the lateral aspect of the sole
during wakefulness. The present study shows that periodic movements in sleep are consistently described by the same features that characterize the Babinski response: dorsiflexion
of the ankle, small toes (with fanning), great toe, and, at times, flexion of the knee and
hip (8). The Babinski response elicited during wakefulness is a reliable index of pyramidal
tract disease. It is thought to be a spinal polysynaptic reflex that is inhibited in normal
people by descending impulses in the pyramidal tract (9,10). The Babinski response has
also been observed as a normal and temporary phenomenon in other situations, such as in
the newborn where its gradual disappearance parallels myelinization of the pyramidal tracts
(9,11). This response is also found normally during recovery from general anesthesia, which
is thought to inhibit supraspinal control of the reflex mechanism (12-15).
Of more importance to the present study is that the Babinski response to plantar stimulation has been reported as a normal occurrence during NREM sleep (9,16,17). Fujiki
et al. (9) studied 14 normal patients in whom a waking Babinski sign was not elicited.
Seven of 14 exhibited a Babinski sign during NREM sleep while there was only one equivocal
response during REM. Three patients with transverse spinal lesions and waking Babinski
signs exhibited a Babinski response to plantar stimulation in REM as well as NREM. It
was concluded that this common NREM phenomenon was due to depression of waking
inhibitory supraspinal influences during NREM that were, however, not depressed in normal
subjects during REM.
It can be concluded, therefore, that the leg movements in PMS not only resemble a
Babinski response, but occur under the same temporary circumstances of NREM sleep (3)
which characterize a normally occurring nocturnal Babinski response. There is further
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R. C. SMITH
clinical evidence that PMS and the Babinski response may be closely related. The high
incidence of clonus in the present study is indicative of pyramidal tract involvement in
PMS, further supporting the contention that the leg movements are related to NREM changes
in pyramidal tract function. Moreover, if the response to general anesthesia is considered
as a model for understanding varying degrees of pyramidal tract suppression, clonus is
found to be the step following the appearance of the Babinski response during recovery
from general anesthesia (14,15). This indicates the close association between the two during
another type of temporary pyramidal tract suppression.
The hypothesis that the leg movements of PMS are Babinski-type responses occurring
without plantar stimulation suggests a central origin of PMS (3). This hypothesis is also
consistent with other neurologic changes in PMS of probable central origin, i.e., periodicity
of the leg movements (18), their association with K-complexes (7), and varying occurrence
of the movements from one leg to the other or in both. In addition, reflex activity has been
reported to be selectively altered during sleep. Not only is the Babinski response depressed
in REM (17), but there is also selective depression of the monosynaptic spinal H-reflex in
humans during REM (19), thought also to be due to descending supraspinal influences
(20). Both monosynaptic and polysynaptic reflexes in the cat are depressed in REM (9).
This hypothesis suggests that a commonly occurring biologic phenomenon, NREM
suppression of inhibitory suprasegmental influences, may be an important predisposing
factor for the development of PMS, and that individual vulnerability to PMS most likely
varies. Thus, the 50% of Fujiki's patients who had nocturnal Babinski responses (9) would
be predicted to be more susceptible. This common loss of NREM supraspinal control could
predispose many individuals to develop either a spontaneously occurring Babinski-like
response or one that occurs from minimal stimulation of the foot or other body part (10,13).
More important than these implications, however, is that the hypothesis itself is in need of
further exploration and testing.
Acknowledgement: The author wishes to thank Janice Weiss, Jeff Sevier, and Janice Herrmann
for their invaluable advice and tireless assistance.
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