Spinal Care, Neurology, Spinal Medical Advice and Information.

Benign Neonatal Sleep Myoclonus


Sudden involuntary brief lightning- like movements of one or more extremities or part of an extremity occur as a normal phenomenon in healthy persons when falling asleep. This happens also in infancy: most parents have seen their babies having such jerks, single or 4 to 5 in series during sleep. In a study done in 1969 Wolf studied the distribution of various spontaneous behavior in sleep in the neonate (startles, sobbing, inspirations, gentle lip ,movements, erections, transient smiles, and twitches of the face and small muscle groups of the limbs) and found myoclonic twitches to be the least frequent. Myoclonic jerks are generally rapid, brief, involuntary, repetitive, irregular and arrhythmic, stereotyped movements that are either focal or generalized and last 0.5 to 5 seconds.

They are different from jitteriness or shuddering which have the characteristics of a tremor. Sleep myoclonus only occurs during the early stages of sleep. In infants with benign neonatal sleep myoclonus, myoclonus was bilateral, synchronous and repetitive, located primarily in the distal parts of the upper extremities and directed toward flexion of fingers, wrist, and elbow. Ankle dorsiflexion myoclonus was also present in two infants. In infants with myoclonic jerks can be repeated for a prolonged period and have been noted to occur for up to 30 minutes continuously in some patients. Infant myoclonus has also occurred synchronously with repetitive sound stimulus.

Myoclonic jerks are associated with discharges in the brainstem reticular activating system, which is also involved with initiation and synchronization of normal sleep. Neonatal sleep myoclonus probably represents a benign disturbance of this brainstem control of sleep. It is not associated with paroxysmal epileptiform EEG discharges and is presumably not a form of epilepsy.

The differential diagnosis of neonatal sleep myoclonus includes myoclonic seizures, benign myoclonus of early infancy, benign familial neonatal seizures, essential myoclonus, and myoclonic jerks in opsoclonus- myoclonus. The essential features of the diagnosis which help differentiate this disorder from other more pathologic disorders include:

1. The seizure type is myoclonic jerks that are partial, generalized or "marching".

2. It appears only during sleep.

3. It lasts from a few minutes to half an hour and can be repeated several times during each sleep period.

4. The general condition of the infant is completely unaffected when the myoclonic jerks continue for a long time.

5. The EEG is normal even during seizures.

6. It starts within two weeks of age often a few days postpartum and generally diminish gradually during the first six months of life.

Infants with this disorder have normal neurologic exams and normal development both at presentation and on extended follow- up. The prognosis for these patients is excellent and treatment unnecessary.