Tremor is defined as an involuntary rhythmical movement and is often categorized in three positions which are: hands in repose (rest), hand held up with arms outstretched (postural), and during movement (intention). The amplitude, frequency and severity of the tremor vary from patient to patient, but at its worst, tremor can cause severe functional disability. There are various causes for tremor. The most common cause being Essential tremor (ET), Parkinson's disease tremor (PD), Multiple Sclerosis tremor, Post Stroke tremor, Post Head Injury tremor etc. The diagnosis of various kinds of tremors is based on the clinical spectrum and radiological imaging.
Essential tremor (ET) is one of the most common tremor disorders. The characteristics of ET is its frequency being 4 - 12 Hz. and it is most pronounced during purposeful movement. This is in contrast to Parkinson's disease tremor which is more dominant during rest. Essential tremor is often hereditary and is transmitted in an autosomal dominant mode. The disease progression of this tremor is fairly benign and it is likely to remain static over a long period of time. Another distinguishing feature of ET tremor is that it mainly involves the upper limb and spares the lower limb unlike PD tremor. At its worst the Essential tremor can be a severe functional handicap preventing the patient from the use of upper extremities. Essential tremor in its initial phase can be well controlled with b-blockers like Propranolol, clonazepam and wysolone. In certain patients the medical treatment fails to give adequate relief from the symptoms. In such patients surgical treatment in the form of thalamotomy or thalamic stimulation should be tried.
In patients suffering from tremors secondary to multiple sclerosis or lesions in the cerebello-rubro-thalamic projections, thalamotomy or thalamic stimulation have been found to be useful in achieving the long-term control of this tremor (video). Though the mechanism of tremor in various disorders is different; the lesioning of the ventro-intermedius nucleus of the thalamus is known to offer effective control of tremors of various etiologies. Thalamotomy
should be performed only unilaterally. Bilateral thalamotomy carries a high risk of speech and cognitive deficits. However in patients having bilateral intractable tremor, we offer bilateral thalamic stimulation without the morbidity of thalamotomy. It has been proved by various trials and also by our personal experience that the thalamotomy of thalamic stimulation or pallidotomy are equally in achieving tremor control. As regards to the thalamic stimulation for Parkinson's disease, a small number of patients have reduced efficacy and tolerance to the deep brain stimulation over a period of time. In this patients, requirement for the current increases over the time. However similar tolerance has not been observed in patients suffering from Essential tremor.