Subthalamic Nucleus Deep Brain Stimulation in Tourette's Syndrome

Background Tourette's syndrome (TS) is characterized by the occurrence, before 18 years of age, of multiple motor and vocal tics, which do not necessarily occur concomitantly. Tics constitute the clinical hallmark of TS; they are sudden, brief, intermittent involuntary (or semi-involuntary) movements (motor tics) or noises (sound tics). Tic severity is variable: some patients have mild or bearable tics, whereas in others tics are so severe to cause bone fractures or cervical myelopathy. Diagnostic criteria set by the Tourette Syndrome Classification Study Group and the American Psychiatric Association are commonly used. It is currently recognized that TS is far more common than previously thought, with a prevalence of 1 to 10 children of adolescents per 1000.

Tics are usually treated in cases where disability at school, in the social environment or at home is severe enough to warrant medical intervention. TS commonly presents with co-morbid features, mainly consisting in obsessive-compulsive traits, attention deficit with hyperactivity disorder and depression. Psychopathologic features are partly an aftermath of tics, particularly in those patients who display severe tics affecting their social and work activities. Therefore, amelioration of tics may substantially improve daily life and adaptation to social and work environments.

Medication is the first choice treatment, with the aim to reduce the intensity of tics and the associated clinical features. Different drugs, belonging to several pharmacologic classes, such as α-adrenergic drugs, typical and atypical neuroleptics, and tetrabenazine are used. In some cases drug treatment provides satisfactory symptomatic benefit. Overall, it is reckoned that a meaningful proportion of TS patients do not have adequate benefit with drug treatment and the majority of patients have side effects of variable severity.

Ablative psychosurgery has been historically used to treat more severe cases of TS, but the results have been disappointing and burdened by irreversible side effects. The recently developed technique of deep brain stimulation (DBS) allows to selectively modulate the activity of brain structures that control movements and behaviors in patients with different neurological disorders. This approach is warranted in those patients who respond poorly to available medical therapy.

Recently, therapeutic DBS trials have been performed in patients with severe TS, who were not satisfactorily controlled by medication. At first, the same thalamic nuclei targeted by ablative surgery, particularly the centromedian-parafascicular (CM-pf) nuclear complex, have been implanted with some success.