Benign sleep myoclonus of infancy is a transient movement disorder that occurs in drowsy or sleeping infants. Its main importance is the possible misdiagnosis as epilepsy and alarm in parents.


Features of benign sleep myoclonus:

(1) Occurrence of unilateral and/or generalized rhythmic myoclonic movements when the infant is drowsy or asleep.

(2) The movements stop when the child is wakened.

(3) The EEG is normal during and after episodes

(4) The onset is usually within a few days of birth.

(5) The condition usually resolves by 3 months of age but may last into early childhood.

(6) Development, movements, reflexes and feeding are all normal.

(7) There may be a family history of sleep myoclonus in siblings or when parents were infants.


An affected infant should not be wakened by shaking.


Reasons for misdiagnosis:

(1) serious concurrent underlying disease present

(2) unilateral movements only

(3) unfamiliarity with sleep myoclonus

(4) association with sleep not recognized


If a patient is misdiagnosed as having epilepsy and given anticonvulsants, then the movements will persist (apparent therapeutic failure). Increasing the dose or adding more medications may make the movements worse by increasing drowsiness.


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