Periodic or rhythmic movements during sleep: Distinguishing clinical features

	Periodic limb movements	Hypnagogic foot tremor and ALMA	Sleep-related rhythmic movement disorder	Restless sleep disorder
Behavior	Repetitive movement of limbs, typically legs, most commonly with triple flexion	Rapid rhythmical movement of one foot or alternating movement of legs	Rhythmical movement (rocking or rolling) of body or head	Frequent nonstereotypic, nonperiodic large body movements involving whole body, arms, legs, and/or head and repositioning
Age of onset	Any	Any	Early childhood	6 to 18 years
Family history	Variable	Unknown	Variable	Unknown
Time of occurrence	First half of the night; most commonly during NREM sleep	Near sleep onset	Before sleep onset	Throughout the night
Frequency	Multiple per night	Nightly	Nightly	Multiple per night
Duration	0.5 to 5 seconds	Usually 4 to 15 seconds, may recur	Seconds to hours	3 to 30 seconds
Memory of event	Variable	Variable	Yes	Child may note sleep disruption
Stereotypical movements	Yes	Yes	Yes	No
PSG findings	Periodic limb movements of sleep	Limb movements	Rhythmical movement artifact near sleep onset	Frequent large muscle movements in all stages of sleep, >5 movements/hour
Associated clinical findings	Commonly seen in association with restless legs syndrome	None (benign)	May be seen in normal children	Iron deficiency

ALMA: alternating leg muscle activation; PSG: polysomnogram.

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