DBS for ET

From WikiCNS
Jump to: navigation, search
Checkmark.gif This article has been reviewed by the NeuroWiki Editorial Board



Essential tremor (ET) is the most common movement disorder (1). In patients who remain refractory to medical therapy, one surgical option is the placement of a deep brain stimulator (DBS) in the ventral intermediate (Vim) nucleus of the thalamus. DBS replaces the physiologic effect of a thalamotomy (by radiofrequency or radiosurgical technique), with the advantages of being adjustable and reversible. There are now numerous studies on the safety and efficacy of DBS for essential tremor (2-5,29).


ET is characterized by bilateral action tremor of the hands and forearms, head, and less commonly voice, in the absence of other neurologic signs (7). The vast majority of patients with ET suffer from mild tremor which can be treated with various medications; however, a smaller subset of patients suffer significant disability. Approximately 10% of patients presenting to a movement disorder clinic suffer from severe motor disabilities, which can be practically defined as any tremor which feeding, drinking, writing, or, in the case of vocal tremor, with communication (8). Although the natural history of ET has not been systematically studied, it is widely accepted that ET is a slowly progressive disease in which major spontaneous improvements are never seen. As ET advances, the frequency of the tremor decreases and the amplitude increases. For these patients, the first line medical treatments include propanolol and primidone (9). For those who fail medical therapy, surgery is an effective option.

Theory behind DBS

The theoretical basis for targeting the Vim nucleus of the thalamus for the relief of tremor is not well understood. Vim receives its major afferent projections from deep cerebellar nuclei which then project to the motor cortex (10). Microelectrode recording of the Vim in patients with essential tremor identifies cells discharging in bursts that are time-locked to the patient's tremor, suggesting that tremor is associated with abnormal discharge in the cerebellothalamic pathway (11). Interruption of this pathway via lesioning or stimulation provides some theoretical basis for the empirical observation of tremor improvement, but a more precise understanding is still unknown. Although the Vim nucleus of the thalamus is the target for both thalamotomy and DBS, the results and side-effect profiles differ between the two therapies. Stereotactic thalamotomy for ET has been performed and patients have been studied for the past fifty years. It is effective in 73 to 93 percent of patients with incapacitating tremor (12-14). However, this destructive lesioning procedure is associated with permanent complications. (12, 13, 15, 16). In addition, bilateral thalamotomy carries an even higher risk of dysarthria as well as debilitating cognitive complications and is thus no longer recommended (17, 18). Given the high rate of complications with bilateral thalamotomy and because of the destructive nature of the procedure, Benabid et al. introduced high-frequency deep brain stimulation using permanently implanted brain electrodes as an effective alternative in 1987 (19). Since that initial publication, DBS has gained in popularity because of its reversibility, adjustability, and lower side effect profile. High frequency stimulation of the Vim nucleus of the thalamus has been shown to be highly effective in the suppression of tremor (4, 19-23). The stimulation provides tremor relief on the contralateral side to the stimulator, completely eliminating tremor in as many as 50% of patients. In the North American multi-center trial, unilateral DBS of the Vim thalamus in 29 patients provided moderate to marked improvement of tremor at one year (2). In a European multi-center study, 89% of 37 patients with ET demonstrated significant tremor relief at one year (4). Recent follow-up studies for both the North American and European multi-center studies have demonstrated maintenance of benefit at two years and six years respectively (5, 21). The results of our study corroborate the improved patient outcome that can be seen with placement of indwelling brain stimulators.


In addition to suppression of the primary symptom of tremor, DBS has been shown to improve quality of life as measured by standardized scales (24). Patients report a dramatic improvement in their handwriting, ability to drink liquids from a cup, and to conduct pursuits they had previously abandoned such as golf and social activities. Schuurman et al. randomized patients with ET to thalamotomy (n=6) or thalamic stimulation (n=7) and demonstrated improved functional status in the thalamic stimulation group as compared to the thalamotomy group as measured with the Frenchay Activities Index (24). Tremor suppression was achieved in both groups at similar rates.

Side Effects

The side effects of thalamic stimulation include dysarthria (in 3 to 18 percent of patients), paresthesias (in 6 to 36 percent), dystonia (in 2 to 9 percent), balance disturbance (in 3 to 8 percent), ataxia (in 6 percent), and limb weakness (in 4 to 8 percent) (2, 23, 25). These side effects are mostly reversible and tolerable as patients prefer to keep the stimulator on despite these side effects. (26) In addition, the neurologic and cognitive complications from DBS appear to be reduced when compared to the complications associated with thalamotomy. In their randomized trial between thalamotomy and thalamic stimulation, Schuurman et al. demonstrated more complications in the patients randomized to thalamotomy (24). In addition, Troster et al. used extensive and sophisticated neuropsychological methods to demonstrate that patients with Vim thalamic stimulation have preserved cognitive functioning (27). Hence, the neurologic and cognitive complications of DBS appear to be lower than that of lesioning methods.

Surgical Technique

DBS surgery is generally performed under local anesthesia using the Leksell stereotactic system (Elekta Instruments, Atlanta, GA) (29). The anterior (AC) and posterior (PC) commissures were noted. Fast inversion recovery sequences in the axial and coronal plane are used to identify the location of the internal capsule, and to help select a safe trajectory from the pre-coronal frontal lobe cortical surface down into the thalamus. The standard thalamic target is: ¼ of the AC-PC distance plus 1-2mm, anterior to PC; ½ the third ventricle width plus 11mm, lateral into the thalamus; depth is at the AC-PC line. The lateral target is adjusted to avoid the medial edge of the internal capsule. A 14mm burr hole is created and the Stim-Lock fixation device is used to secure the lead. The DBS electrode lead is inserted into the thalamus for stimulation testing. Different electrode contacts are used for stimulation, with testing that used 170 to 185 Hertz, a 90 microsecond pulse width, and 0 to 3 volts. If stimulation led to tremor cessation without side effects, the electrode is kept in place. Some centers use microelectrode recording, but this is not typical. For example, if the patient would have described a weak arm or leg, or increased muscle tone, the lead was to be moved medially by 1.5 mm. If numbness or tingling was persistent, the lead was to be moved 2mm anterior. If little or no tremor response was found upon initial lead placement, the lead was to be moved 1-2 mm posterior.

Assessing outcomes

Neurologic improvement in tremor is tested by selecting items from the Fahn-Tolosa clinical tremor rating scale. Surgical complications can include lead breakage, temporary erythema of the pulse generator incision requiring oral antibiotics, pocket site infection, electrode migration (rare with current fixation devices) requiring surgery to pull back the lead, neck or chest injury (rare), and mild hand tingling during stimulation. These types of complications must continue to be carefully documented and carefully considered in the decision to place a deep brain stimulator.


Reference List

  1. Louis ED, Ottman R, Hauser WA. How common is the most common adult movement disorder? estimates of the prevalence of essential tremor throughout the world. [Review] [32 refs]. Movement Disorders 1998;13(1):5-10.
  2. Koller W, Pahwa R, Busenbark K, et al. High-frequency unilateral thalamic stimulation in the treatment of essential and parkinsonian tremor. Annals of Neurology 1997;42(3):292-299.
  3. Koller WC, Lyons KE, Wilkinson SB, Pahwa R. Efficacy of unilateral deep brain stimulation of the VIM nucleus of the thalamus for essential head tremor. Movement Disorders 1999;14(5):847-850.
  4. Limousin P, Speelman JD, Gielen F, Janssens M. Multicentre European study of thalamic stimulation in parkinsonian and essential tremor. Journal of Neurology, Neurosurgery & Psychiatry 1999;66(3):289-296.
  5. Sydow O, Thobois S, Alesch F, Speelman JD. Multicentre European study of thalamic stimulation in essential tremor: a six year follow up.[comment]. Journal of Neurology, Neurosurgery & Psychiatry 2003;74(10):1387-1391.
  6. Fahn S TE, Marin C. Clinical rating scale for tremor. In: Jankovic J TE, ed. Parkinson's Disease and Movement disorders. Munich, Switzerland: Urban and Schwarzenberg, 1993:271-280.
  7. Bain P, Brin M, Deuschl G, et al. Criteria for the diagnosis of essential tremor. Neurology 2000;54(11 Suppl 4):S7.
  8. Louis ED, Ford B, Wendt KJ, Cameron G. Clinical characteristics of essential tremor: data from a community-based study. Movement Disorders 1998;13(5):803-808.
  9. Koller WC, Hristova A, Brin M. Pharmacologic treatment of essential tremor. [Review] [94 refs]. Neurology 2000;54(11 Suppl 4):S30-S38.
  10. Hirai T, Jones EG. A new parcellation of the human thalamus on the basis of histochemical staining. Brain Research - Brain Research Reviews 1989;14(1):1-34.
  11. Lenz FA, Tasker RR, Kwan HC, et al. Single unit analysis of the human ventral thalamic nuclear group: correlation of thalamic "tremor cells" with the 3-6 Hz component of parkinsonian tremor. Journal of Neuroscience 1988;8(3):754-764.
  12. Fox MW, Ahlskog JE, Kelly PJ. Stereotactic ventrolateralis thalamotomy for medically refractory tremor in post-levodopa era Parkinson's disease patients.[comment]. Journal of Neurosurgery 1991;75(5):723-730.
  13. Jankovic J, Cardoso F, Grossman RG, Hamilton WJ. Outcome after stereotactic thalamotomy for parkinsonian, essential, and other types of tremor.[comment]. Neurosurgery 1995;37(4):680-686.
  14. Lenz FA, Normand SL, Kwan HC, et al. Statistical prediction of the optimal site for thalamotomy in parkinsonian tremor. Movement Disorders 1995;10(3):318-328.
  15. Goldman MS, Kelly PJ. Symptomatic and functional outcome of stereotactic ventralis lateralis thalamotomy for intention tremor.[comment]. [Review] [27 refs]. Journal of Neurosurgery 1992;77(2):223-229.
  16. Shahzadi S, Tasker RR, Lozano A. Thalamotomy for essential and cerebellar tremor. Stereotactic & Functional Neurosurgery 1995;65(1-4):11-17.
  17. Matsumoto K, Asano T, Baba T, Miyamoto T, Ohmoto T. Long-term follow-up results of bilateral thalamotomy for parkinsonism. Applied Neurophysiology 1976;39(3-4):257-260.
  18. Selby G. Stereotactic surgery for the relief of Parkinson's disease. 1. A critical review. [Review] [101 refs]. Journal of the Neurological Sciences 1967;5(2):315-342.
  19. Benabid AL, Pollak P, Louveau A, Henry S, de Rougemont J. Combined (thalamotomy and stimulation) stereotactic surgery of the VIM thalamic nucleus for bilateral Parkinson disease. Applied Neurophysiology 1987;50(1-6):344-346.
  20. Hariz MI, Shamsgovara P, Johansson F, Hariz G, Fodstad H. Tolerance and tremor rebound following long-term chronic thalamic stimulation for Parkinsonian and essential tremor. Stereotactic & Functional Neurosurgery 1999;72(2-4):208-218.
  21. Koller WC, Lyons KE, Wilkinson SB, Troster AI, Pahwa R. Long-term safety and efficacy of unilateral deep brain stimulation of the thalamus in essential tremor. Movement Disorders 2001;16(3):464-468.
  22. Obwegeser AA, Uitti RJ, Turk MF, Strongosky AJ, Wharen RE. Thalamic stimulation for the treatment of midline tremors in essential tremor patients. Neurology 2000;54(12):2342-2344.
  23. Pollak P, Benabid AL, Gervason CL, Hoffmann D, Seigneuret E, Perret J. Long-term effects of chronic stimulation of the ventral intermediate thalamic nucleus in different types of tremor. Advances in Neurology 1993;60:408-413.
  24. Schuurman PR, Bosch DA, Bossuyt PM, et al. A comparison of continuous thalamic stimulation and thalamotomy for suppression of severe tremor.[comment]. New England Journal of Medicine 2000;342(7):461-468.
  25. Alesch F, Pinter MM, Helscher RJ, Fertl L, Benabid AL, Koos WT. Stimulation of the ventral intermediate thalamic nucleus in tremor dominated Parkinson's disease and essential tremor. Acta Neurochirurgica 1995;136(1-2):75-81.
  26. Koller WC, Pahwa PR, Lyons KE, Wilkinson SB. Deep brain stimulation of the Vim nucleus of the thalamus for the treatment of tremor. [Review] [31 refs]. Neurology 2000;55(12 Suppl 6):S29-S33.
  27. Troster AI, Woods SP, Fields JA, et al. Neuropsychological deficits in essential tremor: an expression of cerebello-thalamo-cortical pathophysiology? European Journal of Neurology 2002;9(2):143-151.
  28. Kondziolka D, Whiting D, Germanwala A, Oh M. Hardware-related complications after placement of thalamic deep brain stimulator systems. Stereotactic & Functional Neurosurgery 1903;79(3-4):228-233.
  29. Lee JYK, Kondziolka D. Thalamic deep brain stimulation for management of essential tremor. J Neurosurg 103:400-403, 2005.
Personal tools