Index of Suspicion in the Nursery

Abstract

A 3-day-old male infant in the nursery presents with repetitive jerking of his arms and twitching of the chin. The baby was born at term after an uneventful pregnancy. Delivery had been complicated by shoulder dystocia, with a low first Apgar score (4 at 1 min), but the score was 8 at 5 minutes.On physical examination just after birth, no abnormalities were detected except for some jitteriness, and the baby was kept for further observation. A complete blood count and measurement of serum glucose and ionized calcium showed normal values. Ultrasonography of the brain revealed no abnormalities.Now the baby lies in his mother’s arms, appearing asleep, while the continuous jerking movements lead to a mild oxygen desaturation (85% on the oxygen saturation monitor). The mother states that over the past 2 days she has seen similar shorter episodes (lasting 10 to 20 sec) of symmetric jerks of the arms and twitching of the mouth, especially just after feeding, when the baby started dozing off. She denies any (ab)use of drugs during pregnancy, and the family history is negative for epilepsy, although an older sibling also experienced exaggerated jitteriness during the first few months after birth.A bedside maneuver reveals the cause of the condition and, at the same time, extinguishes the movements.A gentle squeeze of the arms of the baby woke him and immediately stopped the seizures, leading to the diagnosis of benign neonatal sleep myoclonus (BNSM).BNSM, first described by Coulter and Allen in 1982, is a distinctive disorder of quiet sleep that frequently is mistaken for true neonatal seizures. (1)(2) The condition usually starts within 3 days after birth and, according to some authors, could be as frequent as neonatal epilepsy. The rhythmic myoclonic movements typically appear when the child is asleep or drowsy and tend to last a few minutes to occasionally 30 minutes. The myoclonic jerks may be partial, multifocal, or generalized, with a frequency of 1 to 15 per second, and immediately stop if the child is awakened. The general condition of the child is unaffected, even during prolonged episodes of myoclonic jerks, and there are no associated abnormalities on neurologic or developmental examination. Neonatal sleep myoclonus by definition is a benign disorder; spontaneous resolution occurs between 2 and 6 months of age, as the sleep pattern matures.A detailed history often is all that is needed to make the diagnosis, especially if findings on the physical examination are unremarkable. In selected cases, electroencephalography (EEG) may be helpful to differentiate BNSM from “true” neonatal seizures. BNSM abnormalities on EEG are conspicuous by their absence. (3)There is no indication for antiepileptic drugs in BNSM because they are not effective and may worsen the condition by inducing drowsiness. (4) Neurologic and developmental deficits do not occur on follow-up.BNSM must be differentiated from neonatal seizures and jitteriness. True neonatal seizures often occur in the setting of a perinatal, metabolic, or infectious insult. Neurologic and developmental assessments frequently reveal abnormalities. True neonatal seizures also may occur during sleep, but a quick arousal of the patient accompanied by abrupt and consistent cessation of the movements strongly speaks against an epileptic origin. Jitteriness consists of symmetric fine rapid movements of the hands and feet (not affecting the eyes) that frequently are stimulus-sensitive and stop if the involved hands or feet are grasped.Myoclonic jerks in a neonate should raise the question of whether the origin is epileptic or nonepileptic. Although this question initially may be difficult to answer, the clinician should evaluate whether the movements occur exclusively during sleep. In this situation, an attempt should be made to awaken the baby. Consideration of BNSM at the initial evaluation of a suspected neonatal seizure disorder, rather than making it a diagnosis of exclusion, can prevent unnecessary investigations, treatment, and parental anxiety.See also Hahn J, Sanger T. Neonatal movement disorders. NeoReviews. 2004;5:e321–e326.