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Hyperekplexia in Neonates Postgrad Med J: First Published As 10.1136/Pmj.77.911.570 on 1 September 2001

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Hyperekplexia in Neonates Postgrad Med J: First Published As 10.1136/Pmj.77.911.570 on 1 September 2001 570 Postgrad Med J 2001;77:570–572 Hyperekplexia in neonates Postgrad Med J: first published as 10.1136/pmj.77.911.570 on 1 September 2001. Downloaded from V Praveen, S K Patole, J S Whitehall Abstract disease) after the Greek word for startle.56 A Hyperekplexia (startle disease) is a rare year later Gastaut and Villeneuve reported 12 non-epileptic disorder characterised by patients without a family history of exaggerated an exaggerated persistent startle reaction startle and corrected the Greek spelling to to unexpected auditory, somatosensory hyperekplexia which has been adopted since.7 and visual stimuli, generalised muscular rigidity, and nocturnal myoclonus. The Introduction genetic basis is a mutation usually of the Startle reflex, a normal reticular and cortical arginine residue 271 leading to neuronal reflex is elicited to a minor degree in normal hyperexcitability by impairing glycinergic newborns and infants.8 It is a basic alerting inhibition. Hyperekplexia is usually famil- reaction consisting of facial grimacing with ial, most often autosomal dominant with blinking, followed by involuntary movements complete penetrance and variable expres- of head flexion, hunching of shoulders, adduc- sion. It can present in fetal life as tion of the arms, and flexion of the trunk and abnormal intrauterine movements, or the knees, causing falling without a protective later at any time from the neonatal period reaction.910 It appears in infancy at the same to adulthood. Early manifestations in- time as the Moro reflex, and becomes more clude abnormal responses to unexpected noticeable as the Moro reflex disappears.11 auditory, visual, and somatosensory When a pathologically exaggerated startle stimuli such as sustained tonic spasm, response interferes with normal activities, exaggerated startle response, and fetal causing apnoea and frequent falls and injuries, posture with clenched fists and anxious the pathological state is termed as startle stare. The tonic spasms may mimic disease or hyperekplexia.310 Hyperekplexia generalised tonic seizures, leading to ap- may occur in a minor form in which the startle noea and death. Consistent generalised response is exaggerated from normal, or a flexor spasm in response to tapping of the major form in which patients present with gen- nasal bridge (without habituation) is the eralised muscular rigidity during the neonatal clinical hallmark of hyperekplexia. Elec- 12 troencephalography may show fast spikes period. initially during the tonic spasms, followed by slowing of background activity with Aetiology eventual flattening corresponding to the The aetiology of hyperekplexia is not clear. phase of apnoea bradycardia and cyano- Hyperactivity of cortical neurons, abnormali- sis. Electromyography shows a character- ties of the inhibitory systems of the brain, and http://pmj.bmj.com/ istic almost permanent muscular activity abnormalities of the serotoninergic pathways 13–16 with periods of electrical quietness. Nerve are among the proposed mechanisms. conduction velocity is normal. No specific Experimental data suggest the importance of computed tomography findings have been nucleus gigantocellularis in the pathogenesis of reported yet. Clonazepam, a gamma ami- the abnormal startle response.17 Subtle brain- nobutyric acid (GABA) receptor agonist, stem vascular anomaly, pontine infarct, lacunar is the treatment of choice for hypertonia posterior thalamic-subthalamic infarcts, and on October 2, 2021 by guest. Protected copyright. and apnoeic episodes. It, however, may not brainstem encephalopathy have been reported influence the degree of stiVness signifi- in adults with hyperekplexia.18–21 Hyperekplexia cantly. A simple manoeuvre like forced is also reported in adults after mild to moderate flexion of the head and legs towards the head injury as part of post-traumatic move- trunk is known to be life saving when pro- ment disorder.22 longed stiVness impedes respiration. (Postgrad Med J 2001;77:570–572) Genetic basis Hyperekplexia is usually familial, most often Keywords: hyperekplexia; neonates; startle Department of autosomal dominant with complete penetrance 23 Neonatology, Kirwan History and variable expression. Autosomal recessive Hospital for Women, Hyperekplexia, or startle disease, is a rare non- form and sporadic cases have also been Townsville, QLD 4817, described.24 The genetic basis is a mutation Australia epileptic disorder characterised by an exagger- V Praveen ated persistent startle reaction to unexpected usually of the arginine residue 271, transform- S K Patole auditory, somatosensory, and visual stimuli, ing â alanine and taurine in the glycine recep- J S Whitehall generalised muscular rigidity in infancy, and tor from agonists into competitive antago- nocturnal myoclonus.12 After its first descrip- nists.25 26 This change aVects chloride Correspondence to: conductance of the -1 subunit of the inhibi- Dr Patole tion in 1958 by Kirstein and Silfverskiold, á SANJAY_PATOLE@ more than 150 cases of hyperekplexia have tory glycine receptors in the caudal pontine health.qld.gov.au been reported so far.34 In 1966 Suhren et al reticular formation leading to neuronal hyper- Submitted 9 January 2001 reported a family of 24 individuals with this excitability by impairing the glycinergic Accepted 12 April 2001 disorder which he named hyperexplexia (Kok’s inhibition.27–29 Recently linkage analysis has www.postgradmedj.com Hyperekplexia in neonates 571 Postgrad Med J: first published as 10.1136/pmj.77.911.570 on 1 September 2001. Downloaded from mapped a gene for this disorder to chromo- (MRSI) studies have shown reduced intensity some 5q33–q35.30 of the neuronal marker N-acetylaspartate, choline containing compounds and creatinine Clinical characteristics in the frontal, central, and right frontal Hyperekplexia can present in the fetal life as regions.12 The topography of EEG abnormali- abnormal intrauterine movements, or later at ties in the frontal lobes has coincided with any time from neonatal period to adult- MRSI findings in some patients. Whether such hood.20 31 The early manifestations include neuronal dysfunction represents cortical dys- abnormal responses to unexpected auditory, function or an epiphenomenon of diencephalic visual, and somesthetic stimuli such as sus- or brainstem abnormalities is currently un- tained tonic spasm, exaggerated startle re- known. No specific computed tomography sponse and fetal posture with flexion of findings have been reported yet. forearm and legs, clenched fists, and anxious stare.3 The tonic spasms may mimic general- DiVerential diagnosis ised tonic seizures, leading to apnoea and The diVerential diagnoses of hyperekplexia in death.32 These spasms are not accompanied by the neonatal period include the congenital epileptic discharges on electroencephalography stiV-man syndrome, startle epilepsy, myoclonic (EEG).33 Additional features are generalised seizures, neonatal tetany, and phenothiazine hypertonia and prominent nocturnal/diurnal toxicity.40 41 Hyperekplexia may also be misdi- myoclonus with apnoea.234 The hypertonia is agnosed as cerebral palsy.7 The diVerential apparent only when the infant is awake.7 Con- diagnoses in adulthood includes neurological sistent generalised flexor spasm in response to disorders with hypertonia like the Issacs tapping of the nasal bridge (without habitua- Mertens syndrome,33 the jumping Frenchman tion) is the clinical hallmark of hyperekplexia, of Maine,42 or somewhat similar clinical entities though its mechanism is not very clear.7 reported in diVerent parts of the world (for Though usually there is neither mental nor example, miryachit in Siberia43 and latah in neurological deficiency, features of diVuse cer- Malaysia and Indonesia44), Gilles de la ebral involvement with developmental delay Tourette syndrome,33 and Swartz Jampel syn- are seen in some patients.35 36 Umbilical, drome.33 inguinal, and diaphragmatic hernias attributed to hypertonia are seen with increasing fre- Treatment quency in the aVected infants.33 Clonazepam, a gamma aminobutyric acid (GABA) receptor agonist, is the treatment of Risk of SIDS choice for hypertonia and apnoeic episodes.45 Sudden infant death syndrome (SIDS) is well The degree of stiVness, however, may not be reported in hyperekplexia.37 38 Central apnoea significantly influenced by clonazepam.46 In related to brainstem dysfunction or peripheral contrast phenobarbitone, phenytoin, di- apnoea after feeding diYculties with conse- azepam, and sodium valproate have not always quent aspiration and respiratory muscle spasm consistently controlled the hypertonia and/or are the proposed mechanisms of SIDS.239 abnormal startle response.3 A simple manoeu- Interestingly, the apnoeic episodes are known vre like forced flexion of the head and legs http://pmj.bmj.com/ to disappear spontaneously by 2 years of age.8 towards the trunk is known to be life saving Sudden death may also be related to complete when prolonged stiVness impedes respiration.47 heart block and apnoea during the seizure-like episodes.32 Conclusion Recognition of hyperekplexia in the neonatal Evolution period is essential in avoiding erroneous Spontaneous amelioration of the hypertonia diagnoses like epilepsy. Diagnosis should not with increasing age and delayed gross motor be diYcult, as consistent generalised flexor on October 2, 2021 by guest. Protected copyright. development characterise the evolution of spasm in response to tapping of nasal bridge hyperekplexia.3 Though the tone is usually (without habituation) is the clinical hallmark.
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