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‘Epilepsy responds to vagus nerve stimulation in ring chromosome 20 syndrome’

‘Epilepsy responds to vagus nerve stimulation in ring chromosome 20 syndrome’ SIR–With reference to the report of ring chromosome 20 (r20) syndrome with intractable epilepsy by Alpman et al.1, we report a 9-year-old male with r20 who has had a good response to vagus nerve stimulation (VNS). Our patient was born at 38 weeks’ gestation and the perinatal period was uncomplicated. Development was within normal limits and there was no family history of neurological conditions. Seizures began at age 5 years, with upward deviation of the eyes, associated with episodes of confusion lasting up to 1 hour. Other seizures took the form of arrest of activity with upward deviation of the eyes, eyelid flickering, and loss of posture, followed by postictal sleep. An ambulatory electroencephalogram (EEG) in the wake state showed variable frequency waveforms in the bifrontotemporal regions, and periods of generalized rhythmic sharp and slow wave activity were demonstrated from both the prefrontal and anterior temporal electrodes. In sleep, there were periods of rhythmic, fast activity followed by diffuse sharp and slow wave bursts from both frontal leads. Our patient had no dysmorphic features; however, based on clinical history, seizure semiology, and EEG findings, karyotyping was requested particularly with reference to r20. This revealed a mosaic pattern with two cell lines – one normal (20% cells) and one ring chromosome 20 (80% cells). Treatment with several antiepileptic medications was unsuccessful, including sodium valproate, lamotrigine (as mono and combination therapy), clobazam, prednisolone, and leviteracetam. In addition, whilst on clobazam, rapid regression of skills occurred, resulting in complete loss of language and ambulation. Video telemetry confirmed the presence of numerous absence seizures, nocturnal tonic–clonic seizures, and periods of non-convulsive status epilepticus. In view of the case report by Chawla et al.2 suggesting some benefit of VNS in a r20 patient, he was referred for the procedure aged 8 years. A Cyberonics model 102 vagus nerve stimulator was implanted in the upper left chest and connected to the left vagus nerve. Implantation was followed by cycles starting at 30 seconds of stimulation followed by 5 minutes off, with a starting current of 0.25mA, increasing to 2.25mA over a 6-month period. An initial good response was observed, with reduction in seizure frequency and the reacquisition of some previously lost skills, including ambulation. Overall affect improved, and eye contact and social smiling returned. Although the generalized tonic–clonic seizures abated, absence seizures continued, although at a significantly decreased frequency, thus the cycling frequency was increased to 30 seconds of stimulation followed by periods of 3 minutes off. A subsequent increase of the stimulation current to 2.5mA led to all seizure types worsening, and prolonged episodes of non-convulsive status were observed. Reduction of current to 2.25mA led to a gradual improvement, with a return to the previous improved state. In contrast to the findings of Alpman et al.1 our experience of VNS in r20 was similar to that previously reported by Chawla et al.2 At present, on a combination of leviteracetam monotherapy and VNS, our patient remains ambulant and seizures are now confined to occasional nocturnal episodes. Treatment of seizures with a benzodiazepine in this patient was associated with worsening seizures and regression of skills, although it is unclear whether this was the natural course of the encephalopathy or a side effect of the medication. We, therefore, recommend that benzodiazepines be used with caution in r20. Vagus nerve stimulation may be a useful clinical treatment and should be considered early in the management of intractable epilepsy associated with r20. Considering our experience, there may be a critical level of stimulation that is most effective, above which the clinical benefit may be lost or seizures may even be worsened.