Benign neonatal sleep myoclonus (BNSM) is a non-epileptic motor
phenomenon that is frequently mistaken for neonatal seizures, resulting
in unnecessary investi-gations and treatments [1]. BNSM is characterised
by myoclonic jerks that occur exclusively during sleep and stop abruptly
when the infant is awakened. In the interictal period, affected neonates
appear well. No treatment other than reassurance is required as the
disorder resolves spontaneously over several weeks without long-term
neurological deficits [1-3]. We describe our experience with benign
neonatal sleep myoclonus seen over 5 years with an aim to create
awareness about this benign disorder.
The data on neonates diagnosed with benign neonatal
sleep myoclonus between February 2010 and January 2015 at a tertiary
care hospital of North India was retrospectively reviewed. Detailed
information about the gestation, adverse perinatal events, age at onset,
asso-ciation with sleep/arousal, and any triggers was noted. Findings on
neurological examination as well as results of laboratory investigations
wherever available were also reviewed. Study was approved by
Institutional review board.
The clinical characteristics of the patients are
summarized in Table I. Interictal
neurological examination was normal in all infants. Normal blood sugar
and serum calcium was documented in all the 15 infants tested.
Electroencephalography was done in 14 cases and was normal in all,
including four with ictal EEG. Five infants each had undergone brain MRI
and CSF analysis before being referred. Once BNSM was diagnosed, parents
were reassured of the benign nature of the disorder and all ongoing
treatments stopped.
TABLE I Clinical Profile of Neonates with Benign Neonatal Sleep Myoclonus (N=18).
Characteristic |
No. (%) |
Full-term gestation |
15 (83) |
Age of presentation, mean (range) d
|
20 (5-60) |
Age of onset, mean (range) d |
9 (2-30) |
Referring diagnosis |
|
Neonatal seizures |
15 (83) |
Sepsis/meningitis |
4 (22) |
Suspected inborn error of metabolism |
2 (11) |
Myoclonus |
2 (11) |
Treatment before referral |
|
Anticonvulsants |
10 (55) |
Megavitamin therapy |
2 (11) |
Antibiotics |
4 (22) |
The infants described in this report had all the
characteristic features of BNSM described in literature [4-7]. The
myoclonic jerks in BNSM have been variously described as focal,
multifocal or generalized and synchronous. Persistently focal myoclonic
jerks as well as involvement of facial musculature is exceptional [1].
The age of onset between 2 to 30 days in our patients was consistent
with that reported in the literature [1]. Some authors have reported
certain manoeuvres to trigger myoclonic jerks in BNSM and facilitate
diagnosis [1,8]. Anticonvulsants, especially benzodiazepines, have been
observed to aggravate myoclonus of BNSM [1].
Misdiagnosis of neonatal seizures is common leading
to unnecessary investigations [1], as seen by us also. Majority had
received treatment with anticonvulsants. Principal reason for diagnostic
confusion with neonatal seizures is the lack of familiarity with BNSM
among physicians. In addition, we observed that the (mis)diagnosis of
neonatal seizures was made by the physicians based on inaccurately
performed and interpreted neonatal EEG. The diagnosis of BNSM can safely
be made on clinical grounds and the diagnostic errors minimized if
characteristic feature of BNSM are kept in mind while evaluating a
neonate with suspicious motor activity [1,4,7]. Neuroimaging, CSF
analysis and other tests are not needed. Most authorities agree that EEG
is not required for its diagnosis [4,6,7].
BNSM is benign self-limiting non-epileptic condition
with excellent outcome. The condition resolves in most by 3 months of
age. Mild speech delay and mildly abnormal axial tone has been noted in
some [1]. Development of epilepsy has been reported in only one
child on follow-up [9]. We do not have long-term follow-up in majority
but one infant was diagnosed with benign infantile convulsions at two
months of age. Treatment with oxcarbazepine resulted in complete
remission. Pediatricians and neonatologists need to be aware of this
non-epileptic condition in the neonates to prevent misdiagnosis of
neonatal seizures.
Contributors: JSG: conceptualized the study,
collected the data and revised the manuscript; GS: performed the data
analysis and wrote the initial draft; HM: performed the literature
review and critically reviewed the manuscript.
Funding: None; Competing interest: None
stated.
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