What is Parkinson’s disease?
Parkinson’s disease is a chronic, progressive and often disabling disease of the nervous system characterized by:
- rigidity (stiffness)
- bradykinesia (slowness of movement)
- tremor (shaking)
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Medications are used to treat the symptoms; the most commonly prescribed drug is a levodopa/carbidopa combination (Sinemet). One unfortunate side effect of levodopa is the development of dyskinesias — abnormal, involuntary movements. Dyskinesias can become a significantly disabling feature of Parkinson’s disease.
As Parkinson’s disease progresses, the symptoms become less responsive to medical therapy. Patients often suffer from the on-off phenomenon, in which their mobility abruptly changes from good (on) to severely impaired (off). For these patients who continue to be severely disabled in spite of optimal medical therapy, surgical intervention should be considered.
Pallidotomy and subthalamic deep brain stimulation are usually the best surgical options for Parkinson’s disease. For patients in whom tremor is the predominant and most disabling symptom, thalamotomy and thalamic deep brain stimulation also are options.
Pallidotomy refers to the creation of a lesion within a structure of the brain called the globus pallidus interna (Gpi). In Parkinson’s disease, Gpi is hyperactive and produces signals within the brain that inhibit movement, thereby causing rigidity and bradykinesia (slowness of movement). By destroying part of the Gpi, a pallidotomy reduces the signals inhibiting movement and can relieve some of the symptoms of Parkinson’s disease.
Rigidity and bradykinesia (slowness of movement) usually improve significantly following pallidotomy. Tremor improves somewhat; however, if tremor is the dominant symptom, thalamotomy or thalamic deep brain stimulation may be more effective. Pallidotomy is especially effective in reducing drug-induced dyskinesias. As a result, many patients will actually increase their dose of Sinemet postoperatively since they are able to tolerate the higher dosing without dyskinesias. The risks of pallidotomy, like those of thalamotomy, are low when only one side is treated but are higher with bilateral treatment.
Subthalamic nucleus stimulation (bilateral)
This treatment is a non-destructive technique for treating Parkinson’s disease. In this procedure, electrodes are implanted into the subthalamic nucleus for chronic stimulation. The stimulation suppresses the hyperactive signals from this nucleus that contribute to the symptoms of Parkinson’s disease.
Bilateral subthalamic nucleus stimulation is effective in reducing rigidity, bradykinesia, tremor, on-off fluctuations and freezing. Patients are usually able to reduce their medication, which often eliminates problems with drug-induced dyskinesias. As with thalamic deep brain stimulation, adjustments can usually be made to minimize side effects.