Stereotactic neurosurgery for Parkinson’s disease
| Parkinson’s disease is a CNS disorder producing a generalized slowness of movement and resting tremor of the hands. Loss of dopamine- producing neurons in the substantia nigra pars compacta is the cause of the condition. Treatment with medications that stimulate an increased production of dopamine by the surviving substantia nigra neurons has revolutionized the management of Parkinson’s disease. Unfortunately, the benefit of the medication tends to lessen after 5 to 10 years of treatment. Increasing difficulty in initiating movement and worsening slowness of movement are features of declining responsiveness of medication. Improved knowledge of basal ganglia circuitry has enabled neurosurgeons to developed surgical procedures to ameliorate some of the effects of the advancing disease.
Degeneration of the dopamine-releasing cells of the substantia nigra reduces excitatory input to the putamen. Inhibitory output of the putamen to the GPe greatly increases via the indirect pathway. This results in decreased inhibitory GPe output to the subthalamic nucleus, which, in turn acts unrestrained to stimulate the GPi. Stimulation of the GPi enhances its inhibitory influences on the thalamus and results in decreased excitatory drive back to the cerebral cortex. Stereotactic neurosurgery is a technique in which a small probe can be precisely placed into a target within the brain. Magnetic resonance imaging (MRI) of the brain defines the three- dimensional location of the GPi. The surgical probe is introduced into the brain through a small hole made in the skull and guided to the target by the surgeon using the MRI coordinates. The correct positioning of the probe into the GPi can be further confirmed by recording the electrical activity of the GPi neurons have a continuous, high frequency firing pattern that, when amplified and presented on a loudspeaker , sound like heavy rain striking a metal roof. When the target location is reached, the probe is heated to a temperature that destroys a precisely controllable amount of the GPi. The inhibitory outflow of the GPi is reduced and movement improves. The use of implantable stimulators to modify activity of the basal ganglia nuclei is also being investigated to improve function in patients with Parkinson’s disease and other types of movement disorder. (GPe and GPi are the parts of globus pallidus) References:
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Filed Under: Neurosurgery • Surgery
