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Therapy in hereditary essential myoclonus (HEM), a disabling movement disorder, is difficult in most cases, especially in regard to the myoclonic syndrome.1 This is the first report on the amelioration (around 65%) of HEM by high frequency deep brain stimulation of the ventral intermediate thalamic nucleus (VIM) in a 61 year old male patient with medically intractable HEM.
The jerky movement disorder began in his neck and shoulders around the age of 6 and gradually progressed, especially in the proximal right arm, leading to a severe reduction of dexterity and inability to write. He was unable to continue working as a janitor when he was 55.
On examination he presented mainly oscillating, “lightning”, irregular, jerky, asynchronous movements of his forehead, neck, proximal right arm, less severe of the left arm, and discreetly of the upper trunk, which was exaggerated by walking, writing or drinking and could be elicited by loud acoustic stimuli. The disorder improved at rest and disappeared in sleep. Additionally, he had a slight torticollis to the left, superimposed by inconstant no-no myocloni and a discrete action tremor of both hands, all of which complies with the HEM criteria as outlined by Quinn.1 The remaining neurological status was unremarkable.
Four of the six children of the patient had possible myoclonus syndrome. Additionally, two of four siblings of our index patient were definitely affected by the movement disorder, whereas the parents seemed to be unaffected (a full account of the family history will be provided elsewhere, manuscript in preparation).
Alcohol consumption markedly attenuated the movement disorder with a clear rebound phenomena after alcohol withdrawal, leading to chronic alcohol misuse. A latent suicidal syndrome with regard to the exhausted medical and social perspectives complicated the situation.
Extensive drug treatment trials (including monotherapy or combination therapy with the following agents: apomorphine, both oral and intrathecal baclofen, cervical application of botulinum toxin, carbamazepine, carbidopa, clonazepam, clonidine, clozapine, fluphenazine, haloperidol, 5-hydroxytryptophan, levodopa, lithium, paroxetine, piracetam, primidone, propranolol, tiapride, trihexyphenidyl, and valproate) had no effect on the myoclonic syndrome except for a mild improvement under diazepam.
Electroencephalography, including back averaging of the EEG activity preceding spontaneous jerks, polymyography, and somatosensory evoked potentials of the median nerve, cranial CT, MRI, and a lumbar puncture did not show any abnormalities.
In this therapeutically hopeless situation, which was complicated by a latent suicidal syndrome secondary to the lacking therapeutical options, unilateral deep brain stimulation of the left VIM (essentially as outlined in Benabid et al 2) was performed after informed consent of the patient, for three reasons: Firstly, VIM stimulation is considered to be a “low risk” and effective therapy in patients with drug refractory essential tremor, which is also characterised by alcohol attenuation.2Secondly, there are anecdotal reports on the improvement of myoclonic disorders by thalamatomy.3 Thirdly, in the absence of a therapeutical effect the electrode could have been removed or switched off.
Intraoperatively and in the subsequent 12 months deep brain stimulation (2.8 V, 130 Hz, 90 μs) produced a pronounced and perstistent reduction of the jerks and the action tremor of the right arm and to a lesser extent of the jerks of the neck and the trunk. The improvement could be postoperatively quantified by a roughly 65% decrease in myoclonus score (table).4 In practical terms, this was reflected by the use of the right hand for handwriting for the first time after 15 years of incapacity. Interestingly, the optimal stimulation parameters corresponded to those used in deep brain stimulation for essential tremor.2 The mild dystonic symptoms (slight cervical dystonia) were not affected by DBS with different stimulation parameters. Preoperative medication comprised 60 mg diazepam a day and could be reduced to 10 mg diazepam a day at 12 months postoperatively.
Stimulation of the VIM is an established neurosurgical method for the treatment of pharmacologically intractable essential tremor, although its mechanisms of action remain to be elucidated.2 It is interesting to note that both diseases (HEM and essential tremor) may be improved by alcohol intake, which could hint at overlapping pathophysiological mechanisms. Importantly, it has been reported that low frequency stimulation (2 Hz-5 Hz) of the VIM in patients with Parkinson’s disease may even trigger mycloni.5 However, we have been unable to aggravate the myoclonic syndrome in our patient by low frequency stimulation (2 Hz-5 Hz), which may point to different mechanisms of actions of stimulus induced myocloni in Parkinson’s disease versus HEM.
In conclusion, this case report suggests that neurostimulation of the VIM may be an effective therapeutic alternative for medically intractable HEM and suggests that the thalamus may be a myoclonus sensitive site.6
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