Monday, July 23, 2007

Neurological Surgery

Deep Brain Stimulation for Parkinson’s treatment

One particularly interesting surgery I was able to observe this week was a deep brain stimulation procedure to treat a Parkinson's patient. Parkinson’s disease results from a lack of dopamine being produced in the substantia nigra, and results in four possible symptoms – tremor of a limb, slowness of movement, rigidity, and poor balance. The patient I observed seemed to exhibit all of these symptoms, with bilateral tremors and rigidity in her arms and legs.

Since no treatment is currently able to prevent or slow the progression of Parkinson’s disease, all treatments aim to treat the symptoms to make life easier. The current options include medication, surgical lesioning, or deep brain stimulation. One common medication is L-dopa, which is converted into dopamine in the brain. Surgical lesioning involves removal of part of the brain that is abnormally active, such as the globus pallidus (pallidotomy). Deep brain stimulation (DBS) can involve the thalamus, subthalamic nucleus, or globus pallidus, all of which are important in the pathway for movement control. It is thought that DBS helps by pacing abnormally firing cells in these regions.

Dopaminergic pathways. Left side is for a normal brain, and right side is for a Parkinson's patient. Red arrows indicate an inhibitory effect and blue arrows indicate an excitatory effect.

Prior to the surgery, Dr. Kaplitt had determined the location of the subthalamic nucleus in the brain by taking an MRI, and had mapped the stereotactic coordinates of this structure. He drilled two holes in the skull and inserted electrodes in the locations indicated by the coordinates. Electrical activity was recorded for a depth range of approximately 20 mm using a 7 micron electrode tip. Using the recordings, the doctors were able to distinguish approximate borders between different areas in the brain - thalamus, subthalamic nucleus (STN), and substantia nigra. It was clearly visible that certain cells in the STN corresponded temporally with the tremors exhibited by the patient. Dr. Kaplitt inserted stimulating electrodes and applied a voltage across these and observed the physiological response of the patient. In certain locations, the applied stimulus was able to visibly decrease tremor and reduce rigidity in the patient's arms and hands. Two days after this procedure, the patient would have a permanent system implanted, much like the one shown in the figure below. The doctor suggested that the deep brain stimulation system in combination with medications would be able to better control the patient's symptoms in the future.

Deep brain stimulator.

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