The case of a baby who had seizures when placed on her stomach has been diagnosed as a rare case of hyperekplexia by South Australian clinicians.
The three month old girl was reviewed in a neurology clinic at Flinders Medical Centre, Adelaide, after having a history of frequent seizures from birth that were not responsive to conventional antiepileptic drugs (AEDs).
The infant had seizures characterised by tonic stiffening of the limbs and cyanosis, lasting two to five minutes. The infant appeared otherwise healthy and extensive investigations including blood tests, EEGs and MRI showed normal results.
The seizures were unresponsive to phenobarbitone, phenytoin, levetiracetam and midazolam, according to Dr Michael Harbord and colleagues from the neonatal unit at Flinders Medical Centre.
The mother reported that the seizures were triggered when the infant was placed on her stomach, but ceased when she was turned on her back. An EEG showed no electrographic seizure activity when tonic stiffening was induced by laying the infant on her stomach. The mother reported that the seizures could also be induced by loud noises or tapping the infant on her nose. Nose tapping was found to result in an exaggerated Moro reflex.
Based on the history and examination findings, the clinicians diagnosed probable hyperekplexia, and this was confirmed when the infant had genetic testing showing homozygous mutations in the SLC6A5 gene.
Anti-epileptic drugs were stopped and the infant showed a dramatic improvement in response to clonazepam, which was built up to three drops (o.45mg) twice daily.
Writing in the Journal of Paediatrics and Child Health, the clinicians report that the infant’s subsequent development was normal, though she did continue to show an exaggerated startle response to nose tapping.
They write that hyperekplexia is an inducible startle response accompanied by increased stiffness and jitteriness, which in time becomes rhythmic and resembles a seizure. The stiffness may also be mistaken as spasticity and a diagnoses of cerebral palsy may be given, they add. In this particular case, the startle reflex may have been triggered when put in the prone position because the baby’s nose touched the mattress, they suggest.
If untreated, an infant may experience prolonged apnoeic episodes which may be fatal. Hyperekplexia may also be exacerbated by beta agonists medications for asthma, they warn.
“Hyperekplexia is a potentially fatal condition associated with prolonged tonic spasms and apnoea. This condition should be considered in the differential diagnosis of neonates who have intractable seizures or episodes of status epilepticus, especially if there is no obvious aetiology; if the EEGs are reported to be normal; and if there is no response to the usual first-line anticonvulsants,” they conclude.