Rationale:
Hyperekplexia HPX is a rare underdiagnosed treatable genetic neuronal disease that exists in both familial and nonfamilial forms, often misdiagnosed as a psychological disease or seizure disorder.
1 The aim of this case report is to describe the clinical variable characteristics of HPX, differentials, and treatments.
Methods:
A 35-year-old male with medical history of depression and anxiety was admitted to our facility and was referred a neurologist for elective Video EEG admission for possible underlying myoclonic seizures and recurrent falls. He describes episodes of sudden body stiffness for few seconds triggered by tactile stimuli, loud noises, emotional stress with intact awareness. He was born term without complicated delivery and no developmental delay. His grandfather had similar but less pronounced symptoms. Mother reported two episodes body stiffness when he was eight months and two years. More symptoms started around the age four to five years when noted to fall after jumping on a solid concrete or if he rubs his nose, as well during the nighttime while sleeping. He describes cautious gate and several scars to the head from falls and quit most of his jobs due to startling episodes. Treated with several depression and anxiety medications without relief, he found alcohol moderately helpful for his symptoms. On the physical exam he had several scars on the back of the head. He startled to nose tapping test, and other tactile stimuli, his general and neurological exam were unremarkable.
Results:
Clinical features helped differentiating seizure from HPX is the stimulus induced episodes which lasts for seconds with intact awareness and short periods of time. Epilepsy estimated prevalence in HPX is 7-12%
and nose tapping test is thought to be the hallmark. Clonazepam is recommended for treatment.2 Patient brain MRI and basic and infectious workup were unremarkable. Video EEG captured startle episodes with electrographic features of nonepileptic myoclonus, including the nighttime episodes. No clinical seizure or interictal epileptiform activity was noted. Other treatments may include carbamazepine, clobazam, phenytoin, diazepam.2 The patient was symptom free on clonazepam nightly and low dose oxcarbazepine within two weeks. Conclusions:
HPX is an underdiagnosed treatable neuronal disease with the hallmark of startle episodes that don’t correspond with epileptiform activity on Video EEG, although minority of patients with HPX may develop seizure disorder. Neuroimaging is unremarkable and diagnosis can be confirmed by genetic testing although may be negative.
Refrences1 Balint B, Thomas R. Hereditary Hyperekplexia Overview. 2007 Jul 31 Updated 2019 Dec 19. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. Gene Reviews Internet. Seattle (WA): University of Washington, Seattle; 1993-2020.
2 Thomas RH, Chung SK, Wood SE, et al. Genotype-phenotype correlations in hyperekplexia: apnoeas, learning difficulties and speech delay. Brain : a Journal of Neurology. 2013 Oct;136(Pt 10):3085-3095. DOI: 10.1093/brain/awt207. PMID: 24030948.
Funding: none