Pallidotomy Health Article

Definition

Pallidotomy is the destruction of a small region of the brain, the globus pallidus internus, in order to treat some of the symptoms of Parkinson's disease.

Purpose

The symptoms of Parkinson's disease (PD) include rigidity, slowed movements, and tremor, along with postural instability and a variety of non-motor symptoms (i.e., symptoms not involving movement). These symptoms are due to degeneration of a small portion of the brain called the substantia nigra, the cells of which secrete the chemical dopamine that influences cells in another brain region called the globus pallidus internus (GPi). Together with other brain regions, these two structures take part in complex control loops that govern certain aspects of movement and, when substantia nigra cells degenerate, these loops are disrupted and movements become unregulated, producing the symptoms of Parkinson's disease.

The effects of dopamine on the brain can be mimicked by the drug levodopa: levodopa therapy is the mainstay of PD treatment in its early stages. Unfortunately, levodopa becomes less effective over time, and also produces unwanted and uncontrolled movements called dyskinesias. This may occur after five to 10 years or more of successful levodopa treatment. Once a patient can no longer be treated effectively with levodopa, surgery is considered as a management option. Pallidotomy is one of the main surgical options for treatment of advanced PD.

The effect of dopamine on the cells of the GPi is to suppress them by preventing them from firing. Pallidotomy mimics this action by permanently destroying the GPi cells. It may seem odd that the treatment for degeneration of one brain area is to destroy another, but in the absence of dopamine, the GPi cells are overactive, and therefore, eliminating them is an appropriate treatment.

The GPi has two halves that control movements on opposites sides: right controls left, left controls right. Unilateral (one-sided) pallidotomy may be used if symptoms are markedly worse on one side or the other, or if the risks from bilateral (two-sided) pallidotomy are judged to be too great.