DBS in the Treatment of Intractable Movement Disorders

Movement disorders are clinical syndromes result from disturbances of basal ganglia function with either an excess of movement or a paucity of voluntary and involuntary movements, unrelated to weakness or spasticity. Movement disorders are synonymous with basal ganglia or extrapyramidal diseases. Movement disorders are conventionally divided into two major categories-hyperkinetic and hypokinetic.

Hyperkinetic movement disorders refer to excessive, often repetitive, involuntary movements that intrude upon the normal flow of motor activity and it includes include Essential Tremors, Dystonia, Chorea, Dyskinesia, and Athetosis.

Hypokinetic movement disorders refer to akinesia (lack of movement), hypokinesia (reduced amplitude of movements), bradykinesia (slow movement) and rigidity. In primary movement disorders, the abnormal movement is the primary manifestation of the disorder. In secondary movement disorders, the abnormal movement is a manifestation of another systemic or neurological disorder.

The basal ganglia include the striatum (caudate. putamen, nucleus accumbens), the subthalamic nucleus (STN), the globuspallidus [internal segment. external segment, ventral pallidum (VP)]. and the substantianigra pars compacta (SNpc) and substantianigra pars reticulata (SNpr).

Surgical therapies for the treatment of movement disorders can be divided into two broad categories: ablative and restorative. The most common structures targeted during stereotactic surgery for movement disorders are the motor thalamus, the globuspallidus internus and the subthalamic nucleus. Ablative surgical therapies for Movement disorders include thalamotomy and pallidotomy. Restorative surgical therapies include deep brain stimulation and transplantation of fetal tissue, cell lines that express trophic factors, or somatically delivered gene therapies. The theoretical advantage of Deep Brain Stimulation over ablative procedures is the lack of tissue destruction especially with deep brain stimulation. This is particularly appealing for patients needing bilateral procedures.

Parkinson's disease is the best example of a hypokinetic movement disorder. The interest in surgery has been prompted by the growing realization of the limitations of drug therapy for these movement disorders, improvement in neuroimaging capabilities, enhanced stereotactic surgical techniques and better understanding of functional organization of the basal ganglia and its pathophysiology of these movement disorders. There are many theories on how does Deep Brain Stimulation works in the treatment of movement disorders, these theories include Neurostimulation, Neuroinhibition, and Release of neurotransmitters. Deep brain has the following advantages over ablative surgery: No destruction of brain tissue can adjust stimulus parameters, Perform bilateral operations, significant reduction (50-75%) in medication, and it is completely reversible.

Since the introduction of deep brain stimulation almost 20 years ago, there has been an immense resurgence in interest in the surgical technique. However, the investigators are still asking some of the same questions. How can the investigators improve the targeting? What is the optimal target? In addition, the investigators have started asking some new questions such as how does deep brain stimulation work, and what other disorders can deep brain stimulation be applied to?