Sleep-Related Movement Disorders

Some movement disorders and behavioral disorders appear specifically during sleep or in relation to sleep. These are rapid eye movement (REM) sleep behavior disorders (RBD); restless legs syndrome; periodic limb movement in sleep (PLMS); cataplexy, which manifests itself as sudden falling, head dropping, or jaw dropping due to sudden loss of muscle tone triggered by emotions (laughing in particular); hypnic jerks or hypnagogic myoclonus; fragmentary myoclonus in children; autosomal dominant nocturnal frontal lobe epilepsy; sleep walking and sleep terrors; head banging, and bruxism (grinding of the teeth). Careful history taking or reviewing a home video provides valuable clues, but the gold standard remains video polysomnography (PSG). Some sleep-related movements do not represent “disorders” as such but are harmless, physiological motor phenomena, and are discussed because of their frequency and relevance in differential diagnostic considerations.