The observable clinical manifestations may consist of rapid, hyperkinetic movements as well as tonic/dystonic posturing of the limbs. Other potential manifestations include brief arousals from sleep or wandering ambulatory behavior. Non-motor manifestations (such as sensory or emotional phenomenon) are common and retained awareness during seizures may occur. Seizures usually occur during non-REM sleep. The frequency of seizures can be very high and as many as dozens may occur every night which results in poor sleep quality. In addition, many patients with SHE suffer from cognitive impairment and have behavioral/psychological problems. There are many risks associated with nocturnal seizures including concussion, suffocation and sudden unexpected death (SUDEP). Cause
Approximately 86% of SHE cases are sporadic, 14% of patients have a family history of epilepsy and 5% are inherited in an autosomal dominant manner (i.e. autosomal dominant sleep-related hypermotor epilepsy). Both genetic, structural and multifactorial etiologies can occur. In structural cases, the most common pathology is focal cortical dysplasia.The first described mutation in SHE was found in genes coding for the neuronal nicotinic acetylcholine receptor. Since then multiple other genes have been identified including KCNT1, DEPDC5, NPRL2, NPRL3, PRIMA1, CABP4, CRH and others. In some cases, structural and genetic etiologies can coexist such as with mutations in DEPDC5. Diagnosis
The condition may be difficult to diagnose and misdiagnosis is common. The subject may be unaware they have a seizure disorder. To others, the involuntary movements made during sleep may appear no different from those typical of normal sleep.
People who have nocturnal seizures may notice unusual conditions upon awakening in the morning, such as a headache, having wet the bed, having bitten the tongue, a bone or joint injury, muscle strains or weakness, fatigue, or lightheadedness. Others may notice unusual mental behaviors consistent with the aftermath of a seizure. Objects near the bed may have been knocked to the floor, or the subject may be surprised to find themselves on the floor. Diagnosis is based on clinical history but often EEG and/or polysomnography is required. In many patients the EEG can also be unhelpful as seizures may originate from deep in the brain. Polysomnography can be helpful distinguishing SHE from parasomnias as they often arise from different stages of sleep. Treatment
Like other forms of epilepsy, SHE can be treated with anti-seizure medications. Adequate control of seizures occur in approximately two-thirds of patients with anti-seizure medications while approximately one-third of patients do not appropriately respond. The relative efficacy of different medications has not been systematically investigated. Historically, low-dose carbamazepine has been the preferred medication for SHE and is often considered to be first-line. Other anti-seizure medications which have been studied for the treatment of SHE and found to have efficacy include: oxcarbazepine, topiramate, lacosamide and perampanel. Epilepsy surgery can be efficacious in refractory patients. In addition, there have been reports of successfully treating SHE due to mutations in CHRNA4 with nicotine patches. References
Sources
Manford, Mark (2003), Practical Guide to Epilepsy, Butterworth-Heinemann, ISBN 978-0-7506-4621-5