Thalamic deep brain stimulation for essential tremor

Scenario

A 68-year-old male is referred to discuss deep brain stimulation surgery for his upper extremity tremor, which has been characterized as essential tremor, also known as benign familial tremor. He reports a long history of tremors which began in early adulthood and initially were not bothersome. As they worsened over the years, he was initially treated with propranolol which improved his tremors, although it had to be discontinued secondary to hypotension. Primidone was tried as well, with limited efficacy. Alcohol intake significantly reduced his tremors, and his family history was significant for multiple family members (brother, father, grandmother) with similar tremor, although each with varying severity. Physical examination was significant for a mild, barely noticeable right-sided rest tremor, which worsened dramatically with sustention and intention. Gait was mildly ataxic. Spiral drawing revealed significant difficulty with an almost unintelligible signature. The patient was not able to drink from a cup without spilling.

• Variation : Tremor differences in Essential Tremor (ET) versus mixed Essential-Tremor-Parkinsons Disease (ET-PD) phenotype -- A patient with a similar long history who also demonstrates bradykinesia and rigidity on examination may represent a mixed ET -PD phenotype, i.e., patients who develop other parkinsonian symptoms after a long history of only tremor. Similarly, while “classic” essential tremor is an intention tremor and as such can be contrasted with “classic” Parkinsonian tremor, severe essential tremor can assume a rest component, just as severe Parkinsonian tremor can assume an intention component. If a patient referred for deep brain stimulation (DBS) with ET is noted to have additional Parkinsonian symptoms, consideration for a different DBS target (subthalamic nucleus (STN) or globus pallidus pars interna (GPi)) should be given. Moreover, patients with tremor-predominant Parkinson's disease (PD) may be referred with the incorrect diagnosis of ET, and as always, a careful history taking and physical examination should be performed, with a recommendation for an evaluation by a qualified movement disorder specialist.

• Variation : The patient has primary head and voice tremor -- While upper extremity tremor is the primary indication for surgical intervention, a proportion of patients will present with severe head tremor and/or voice tremor. Frequently, these patients have concomitant extremity tremor, but occasionally a patient with insignificant arm tremor, but with severe head/voice tremor, may be referred for intervention. If so, bilateral intervention would be indicated, as midline tremor is most responsive to bilateral intervention.

• Variation : The patient has tremor secondary to multiple sclerosis -- Patients with multiple sclerosis (MS) frequently suffer from severe intention tremor. DBS for MS tremor may afford functional improvement in a subset of these patients; however, many of these patients have a severe ataxic component to their tremor, and despite well-performed thalamic DBS surgery, improvement in overall function and quality of life may not be sustained. There is currently no clear indicator preoperatively if patients are more or less likely to respond to Vim DBS therapy.