Abstract
Severe myoclonic epilepsy in infants (SME) is one of the most malignant epileptic
syndromes recognized in the latest classification of epileptic syndromes. The clinical
details and electroencephalographic (EEG) characteristics have been elucidated by
Dravet et al. The diagnosis of SME depends largely on the combination of clinical
and EEG manifestations at different ages, of which the presence of myoclonic seizures
appears to be the most important. However, because of the inclusion of different types
of myoclonic attack and the lack of strict criteria for diagnosing SME, there has
been some confusion as to whether patients without myoclonic seizures or myoclonus
should be classified as SME, despite other identical clinical symptoms (SME borderlands
(SMEB) group). Among the various clinical manifestations characterizing SME, special
attention has been paid to seizures easily precipitated by fever and hot baths in
Japan. We have demonstrated that the onset of myoclonic attack in these patients is
very sensitive to the elevation of body temperature itself rather than its etiology.
Using simultaneous EEG and rectal temperature monitoring during hot water immersion,
we showed that epileptic discharges increased in frequency, and eventually developed
into seizures at temperatures over 38°C. We believe that the unique fever sensitivity
observed in SME is similar to, but more intense than that of febrile convulsions.
We have also identified a group of cases who have had innumerous myoclonic and atypical
absence seizures daily which were sensitive to the constant bright light illumination.
In these cases, spike discharges increased or decreased depending on the intensity
of constant light illumination. Although these cases form the most resistant SME group,
they lost the constant light sensitivity with increasing age, leaving only relatively
common types of fever-sensitive grand mal seizures (FSGM) at the age of around 5 years.
In the long run, only convulsive seizures continue, while myoclonic or absence seizures
and photosensitivity disappear with advancing age, thus it is conceivable that SMEB
constitutes a basic epileptic condition underlying SME. There is a clinical continuum
that extends from the mildest end of SMEB to the severest end of SME with constant
light sensitivity, with intermediates of frequent or infrequent myoclonic and absence
seizures in-between. This spectrum concept appropriately explains the clinical variabilities
between SME and SMEB during early childhood.
Keywords
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Article info
Publication history
Accepted:
July 13,
2001
Received in revised form:
July 10,
2001
Received:
June 7,
2001
Identification
Copyright
© 2001 Elsevier Science B.V. Published by Elsevier Inc. All rights reserved.
