Indian Pediatrics 2001; 38: 81-83
Benign Neonatal Sleep Myoclonus
Neonatal sleep myoclonus is a benign disorder characterized by myoclonic jerks occurring only during sleep and presenting in the first month of life. The condition is self-limited, requires no treatment and is unassociated with any developmental and neurological deficits(1,2). The fact that benign neonatal sleep myoclonus (BNSM) is an innocuous and non-epileptic phenomenon is not well recognized(2,3). Not uncommonly, BNSM is confused with neonatal seizure disorder, resulting in unnecessary investiga-tions, treatment and parental anxiety(1,2). Here we describe 2 cases of BNSM with an aim to create awareness about this condition.
Case 1: A 9-day-male infant, weighing 3.15 kg, and on exclusive breast feeds presented with multiple episodes of abnormal jerks affecting all the four limbs, not associated with any change in color. In between the episodes he was active, and feeding well. This baby was born at home following an uneventful term gestation, to a second gravida mother. Baby had cried immediately at birth and the postnatal period was unremarkable. At admission baby was awake, alert, had no neurodeficits or abnormal movements. Blood glucose, calcium, CSF examination and septic work-up were all normal. Treatment with intravenous dextrose, calcium, phenobarbital, phenytoin and pyridoxine did not prevent recurrences of myoclonic jerks. CT scan head and sleep EEG record did not reveal any abnormality. Possibility of BNSM was considered. Review of history with mother revealed that jerks occurred during sleep only, an observation confirmed during the hospital stay of the baby. Anticonvulsants were tapered gradually. Myoclonus disappeared by 5 months of age. At 1½ years of follow-up child had normal neuro-logical and developmental examination.
Case 2: A 2.6 kg male baby was born following an uneventful term gestation. Baby had normal Apgar scores and was on exclusive breast feeds. On the 4th day of life, myoclonic jerks of all the 4 limbs were observed. The episode lasted for about 15 minutes and was not associated with any change in color or activity. Two such episodes were noticed on 5th and 6th day of life. Physical examination of the baby was unremarkable. Initial investigations revealed hypocalcemia (serium calcium 6.9 g/dl). Treatment with intravenous calcium resulted in normalization of serum calcium but myoclonic jerks persisted. Treat-ment with magnesium, phenobarbital and pyridoxine was also a failure. A sleep electro-encephalogram (ECG) did not show any abnormal discharges. A diagnosis of BNSM was considered. Later jerks were observed to be occurring during sleep only and dis-appeared when the baby was awakened. These finding were corroborated by mother also. Parents were reassured and baby discharged home without any antiepileptic medication. Myoclonic jerks disappeared by 3 months of age and at 11 months of age baby had normal neurodevelopment examination.
Benign neonatal sleep myoclonus (BNSM) has been described only recently(4). Coulter and Allen in 1982 described 3 infants, who had sleep myoclonus that began in the neonatal period. The myoclonic jerks were bilateral, repetitive and located mainly forearms and hands. Neurological examination and EEG were normal and remained normal during follow-up. They coined the term BNSM for this phenomenon(4). Subsequently till 1992 about 34 cases of BNSM had been described in the literature(2). It is possible that cases of BNSM are treated as neonatal seizures resulting in under diagnosis of the entity(2,3).
Several features of BNSM help in its recognition as well as its differentiation from neonatal seizures. Though the myoclonic jerks in BNSM can be focal, multifocal, generalized or marching(1,2,5) and mimic neonatal seizures, they characteristically appear only during sleep(1,8). More important they stop abruptly and consistently when the child is aroused(1,2,5). This latter finding needs to be elicited in all cases where a diagnosis of BNSM is considered, as it differentiates BNSM from a neonatal seizure more emphatically than its occurrence during sleep (neonatal seizures can occur during sleep). The general condition of the child is completely unaffected, even during prolonged episodes of myoclonic jerks(1), and there are no associated abnormalities on neurological or develop-mental examination(1,7). There is evidence that jerks of BNSM may be enhanced or precipitated by sound, touch, rocking or even benzodiazepines (2,4). True neonatal seizures, on the other hand, in most circumstances occur in the setting of perinatal, metabolic or infectious insult(9,10). Seizures do not necessarily occur during sleep, are frequently associated with change in color (cyanosis) and abnormalities on neurological and develop-mental assessment are frequently present.
Concommitant EEG abnormalities are conspicuous by their absence in BNSM(1,2). This has been confirmed by long-term video-electroencephalographic monitoring(8). How-ever, an EEG is not essential for diagnosis if attention is paid to the clinical information, but may be required to distinguish BNSM from benign neonatal convulsion(2). Neonatal sleep myclonus is benign and self limited disorder and spontaneous resolution occurs between 2 to 6 months of age. Neurological and developmental deficitis do not occur on follow-up(1,2,5). Both the cases described by us fit well into the above description of BNSM. Follow-up showed spontaneous resolution of the condition and normal neurodevelopment.
BNSM is frequently misdiagnosed, there-fore, investigated and treated as a neonatal seizure, as happened initially in our cases, especially the Case 1. This reflected a lack of awareness, about the disorder. Since sponta-neous resolution occurs by 6 months in almost all the patients, it may be incorrectly attributed to anticonvulsant medication and true diagnosis of BNSM never made.
BNSM should be considered as a differential diagnosis of neonatal seizures especially when seizure like activity occurs in a neurologically normal newborn. Occurrence of jerks during sleep and their disappearance on arousal should suggest a diagnosis of BNSM. Consideration of BNSM at the initial evaluation of a suspected neonatal seizure disorder, rather than making it a diagnosis of exclusion would prevent the unnecessary investigations and treatment.
JSG conceived the idea and drafted the paper. BP and VRP helped in
drafting the paper.