Diagnosis and Clinical Characteristics of Periodic Limb Movement Disorder

Diagnostic Criteria

The American Academy of Sleep Medicine recommends polysomnographic confirmation of Periodic Limb Movement Disorder (PLMD) with a PLMS Index exceeding 15 per hour in adults, along with clinical sleep disturbance or daytime fatigue that is not better explained by another disorder 1
PLMD is a diagnosis of exclusion, requiring ruling out other sleep disorders, medical/neurological disorders, mental disorders, medication use, or substance use disorders 1

Up to 90% of individuals with Restless Legs Syndrome (RLS) have periodic limb movements, but PLMs are neither necessary nor sufficient to diagnose RLS 1
The American Geriatrics Society notes that RLS is diagnosed clinically by history alone without requiring polysomnography in most cases, and features an uncomfortable urge to move the legs with dysesthesias, worsening at rest and in the evening, relieved by movement 2
Nocturnal leg cramps are painful, involuntary muscle contractions with no urge to move the legs, and relief comes from stretching the affected muscle, not general movement 1

The movements in PLMD are rhythmic, stereotyped extensions of the big toe and dorsiflexions of the ankle, occasionally with knee and hip flexions, each lasting approximately 2 to 4 seconds with a frequency of about 1 every 20-40 seconds 1
These movements may cause brief awakenings or arousals that the patient may not be aware of 1