Neuromodulation in dystonia: current aspects of deep brain stimulation

Among the surgical treatment options for patients with medically refractory dystonia chronic deep brain stimulation (DBS) of different targets in the basal ganglia circuitry has become one of the most important tools. The globus pallidus internus nowadays is the target of choice, while there is only limited experience with other targets. At this time, patients with primary (genetic or sporadic) generalized and segmental dystonia, and patients with (complex) cervical dystonia are thought to be the best candidates for pallidal DBS. Advantages of DBS are its reversibility, its adjustability, and the continuous access to modify the target in the basal ganglia. The present review gives an account on the development of surgical neuromodulation therapy for dystonia, surgical approaches, hardware-related problems, DBS programming and patient management, and clinical outcome. Studies conducted according to the practices of evidence-based medicine confirm the results of early pilot studies. The wide majority of patients achieve beneficial lasting outcome at a relatively low rate of manageable side-effects. Along with improvement of the movement disorder, studies report on amelioration of quality-of-life surrogates. We also provide an overview on DBS surgery in less common dystonic syndromes, such as craniofacial dystonia, status dystonicus, task-specific dystonia, paroxysmal dystonia, camptocormia, and secondary dystonias, including choreoathetosis, hemidystonia, tardive dystonia, and pantothenate kinase-associated neurodegeneration. Furthermore, we discuss the implications of intra-operative microelectrode recordings and pallidal field potentials for the pathophysiology of dystonia and the particular possible mechanisms of DBS in dystonia. Finally, future perspectives are outlined.