Deep Brain Stimulation in the Treatment of Intractable Movement Disorders ( Parkinson's Disease, Essential Tremors and Dystonia)

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.