What is benign neonatal sleep myoclonus (BNSM)?

From the Guidelines

Benign neonatal sleep myoclonus is a self-limiting condition that does not require treatment, as it resolves on its own, typically within the first few months of life. This condition is characterized by rhythmic jerking movements that occur exclusively during sleep, often involving the limbs, particularly the arms, and can be bilateral and synchronous 1. The myoclonic jerks may increase when the infant is touched or stimulated during sleep, but the key distinguishing feature is that these movements stop immediately when the baby wakes up.

Key Characteristics

• The condition is benign and harmless, with no indication of a seizure disorder or neurological problem
• The myoclonic jerks occur exclusively during sleep, and stop when the baby wakes up
• The condition is self-limiting, resolving spontaneously within the first few months of life
• No treatment is necessary, and parents should be reassured about the condition's benign nature

Diagnosis and Management

• Diagnosis is primarily clinical, based on observation of the characteristic movements exclusively during sleep
• EEG monitoring during an episode would show no epileptiform activity, confirming the benign nature 1
• Parents should be educated about the condition's benign nature to reduce anxiety, and no medication or intervention is required
• The exact cause remains unknown, but it's believed to relate to immature brain development, similar to benign myoclonus of early infancy (BMEI), which is characterized by myoclonic jerks of the head and/or upper limbs, usually occurring in clusters and mimicking infantile spasms 1

From the Research

Definition and Characteristics

• Benign neonatal sleep myoclonus is a disorder characterized by abnormal episodic jerky movements that occur exclusively during sleep 2.
• It is a non-epileptic disorder, often confused with epileptic neonatal seizures 3, 4.
• The myoclonus often increases with gentle restraint and can mimic convulsive status epilepticus and serial seizures 3.

Diagnosis and Differential Diagnosis

• A confident diagnosis can usually be reached when the history is suggestive, and physical examination and basic investigations are normal 2.
• Benign neonatal sleep myoclonus must be included in the differential diagnosis of neonatal seizures 3.
• It should be considered early in the differential diagnosis of neonatal seizures to avoid misdiagnosis 5.

Prognosis and Treatment

• The condition resolves spontaneously within the first year, most often within the first three months, with no sequelae 2.
• It is not associated with perinatal complications and does not compromise future development 4.
• Treatments, including anticonvulsant therapy, can be withdrawn once the diagnosis of benign neonatal sleep myoclonus is made 3, 5.

Genetics

• Benign neonatal sleep myoclonus can show autosomal dominant inheritance and is not allelic with benign familial neonatal seizures 6.
• The loci for KCNQ2 and KCNQ3, the genes that cause most cases of benign familial neonatal seizures, were excluded in some families with benign neonatal sleep myoclonus 6.