Sleep-Related Movement Disorders
Restless legs syndrome (RLS)
RLS is a clinical diagnosis requiring all five criteria: (1) urge to move the legs, usually with uncomfortable sensation; (2) onset or worsening with rest/inactivity; (3) relief with movement; (4) worsening in the evening or night; and (5) not better explained by another condition. It is associated with iron deficiency; ferritin and iron studies are appropriate. Dopamine agonists, alpha-2-delta ligands (gabapentin, pregabalin), and iron repletion are treatment options; augmentation is a key complication of dopaminergic therapy.
Periodic limb movements and bruxism
Periodic limb movements of sleep (PLMS) are scored on PSG as movements lasting 0.5–10 seconds in series of ≥4, with an index (PLMI) >15/hour in adults considered elevated (age-dependent in children). PLMS are supportive but not diagnostic of RLS-many people with PLMS have no RLS, and vice versa. Sleep-related bruxism involves rhythmic masticatory muscle activity, often with arousals; it can cause dental damage and jaw pain.
Traps: diagnosing RLS from PLMS on PSG alone; overlooking iron deficiency; missing augmentation (earlier onset, more intense symptoms, spread to other body parts) in patients on dopamine agonists; and confusing RLS with nocturnal leg cramps (which are not relieved by movement in the same way and are not circadian).
Rule of thumb: RLS is diagnosed by history; PSG is for excluding mimics or quantifying PLMS, not for making the RLS diagnosis.
Worked example: A patient with evening urges to move, relief with walking, and ferritin 20 ng/mL should receive iron repletion evaluation before dopamine agonists.