Additional approaches to the treatment of Parkinson's disease include surgical procedures, brain stimulation, and transplantation of dopaminergic cells. In general, surgical procedures are reserved for patients who are refractive to levodopa or who have profound dyskine-sias or fluctuations in response to levodopa. Tremor can be abolished by ablation of the ventral intermediate nucleus of the thalamus. Dyskinesias can be effectively controlled by ablation of the posteroventral portion of the globus pallidus. Brain stimulation appears to be a promising technique. High-frequency electrical stimulation of the thalamus, subthalamic nucleus, or globus pal-lidus can improve various symptoms of parkinsonism and reduce levodopa dosage.
A potentially promising, although very controversial, approach to the treatment of Parkinson's disease is replacement of dopaminergic neurons. The grafting of fetal substantia nigra tissue, which contains the dop-amine neurons, into the striatum of parkinsonian patients has been modestly successful. The procedure will remain experimental, however, until the many practical problems and ethical issues associated with the use of fetal tissue are resolved. The discovery of pluripotent stem cells is also being viewed as a possible way of developing dopamine neurons for transplant purposes.
Alzheimer's disease, the most prevalent form of dementia, afflicts approximately 10% of the population over age 65. The cardinal features of Alzheimer's disease are progressive loss of memory and disordered cognitive function. Alterations in behavior and a decline in lan guage function can also be observed in the early stages of Alzheimer's disease. The impairment in cognitive abilities occurs gradually, with the loss of short-term memory generally preceding loss of long-term distant memory. In the advanced stages, the individual may not recognize spouse or children, and the levels of arousal and alertness are severely impaired. Other signs of Alzheimer's disease include reduced verbal fluency, naming deficits, and impairment of speech exemplified by failure to arrange words in proper order (dysphasia). Ultimately, with progression of the disease, motor function is impaired and the patient may fall into a vegetative state. Death is usually associated with complications of immobility (e.g., pneumonia or pulmonary embolism).
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