Morvan syndrome and related disorders associated with CASPR2 antibodies
Jan. 23, 2023
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In this article, the author highlights the clinical characteristics of benign sleep myoclonus of infancy (BSMI), which was recently relabelled "benign polymorphous movement disorder of infancy" (BPMDI) (Álvarez et al 2021). Benign sleep myoclonus of infancy is a movement disorder that typically starts within the first 15 days of life, occurs during sleep, and consists of intermittent repetitive jerks of the limbs at two to three per second. It is often evoked by gently restraining the child. Benign sleep myoclonus of infancy is usually not associated with any other neurologic impairment and spontaneously subsides within the first year of life. Its importance lies in the differential diagnosis with the epileptic, especially myoclonic, seizures of infancy. Benign sleep myoclonus of infancy can be mistaken for neonatal seizures or even neonatal status epilepticus; the recognition of benign sleep myoclonus of infancy is imperative to avoid unnecessary diagnostic studies and treatments.
• Benign sleep myoclonus of infancy consists of myoclonic jerks that involve limbs, trunk, or the whole body, occurring in clusters during quiet NREM sleep and disappearing during wakefulness.
• Benign sleep myoclonus of infancy occurs in early life, typically from birth to six months of age.
• Benign sleep myoclonus of infancy is not associated with EEG abnormalities and occurs in otherwise neurologically normal children.
• Benign sleep myoclonus of infancy may be induced by repetitive sound stimuli and by gently restraining or by rocking the child, especially in a head-to-toe direction.
• Benign sleep myoclonus of infancy should be especially differentiated from the epileptic myoclonus that occurs during infancy, and requires no treatment.
Benign sleep myoclonus of infancy was first reported in 1982 as benign neonatal sleep myoclonus (10). Lombroso and Fejerman, in 1977, described nonepileptic movements in normal infants and named them "benign myoclonus of early infancy," which were recently relabelled by Fernández-Álvarez as "benign polymorphous movement disorder of infancy" (BPMDI). A new proposed definition that is simple to remember is "transient infant movements" (TIM) (29).
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