Dementia due to Parkinson’s Disease
Clinical Features and Treatment
Although dementia Opens in new window rarely occurs as an initial symptom of Parkinson’s disease Opens in new window, it is found in nearly 40% of such patients older than 70 years of age. Approximately one million people in the United States have the disease with 50 000 new cases being diagnosed on yearly basis. The prevalence for persons over age 60 is 1%.
The disease results from loss of dopamine production in the basal ganglia, and can be idiopathic or postencephalitic. Usually the patient is 50 years of age or older, and unlike Alzheimer’s and Pick’s dementias, this disease occurs slightly more often in men. Dementia most commonly occurs in cases of Parkinson’s disease in which the decline has been rapid and response to anticholinergics has been poor.
The clinical features of Parkinson’s disease are well described, with the cardinal triad being tremor, rigidity, and bradykinesia. Associated features include postural instability, a festinating gait, micrographia, seborrhea, urinary changes, constipation, hypophonia, and an expressionless facial countenance.
The tremor in Parkinson’s disease has a regular rate and is most prominent when the patient is sitting with arms supported; it has therefore been described as intention tremors. Paranoid delusions and visual hallucinations may occur, but auditory hallucinations are rare. Antipsychotics with low incidence of entrapyramidal symptoms such as quetiapine are recommended.
The pharmacological treatment of Parkinson’s disease involves the use of a number of categories of medication. These include selegiline, a selective monoamine oxidase inhibitor, levodopa and other dopamine agonists (e.g. pramipexol, bromocriptine, pergolide mesylate, amantadine), and various anticholinergic agents (e.g. benztropine).
Selegiline should not be given to patients on antidepressant medication, and there is a risk that dopaminergic agents may produce/activate psychosis or mania and anticholinergic drugs may increase confusion.
When discontinuing levodopa after a long course of treatment, the drug should be tapered so as to prevent a discontinuation syndrome similar in nature to the neuroleptic malignant syndrome.
Some medications (metoclopramide, droperidol, several antipsychotics) may produce Parkinsonian features such as masked facies, sparsity of speech, and tremor) and in those cases the appropriate course of treatment is to discontinue the offending medication.
Several researchers are looking into the possibility of using embryonic stem cell implant as treatment for Parkison’s disease and several other conditions. Deep brain stimulation (DBS) is a surgical procedure used to treat Parkinson’s disease in those patients whose symptoms cannot be adequately controlled with medication.
DBS uses a surgically implanted, battery-operated medical device called a neurostimulator to deliver electrical stimulation to targeted areas of the brain that control movement, blocking the abnormal nerve signals that cause tremor and other Parkinson’s disease symptoms.
The usual targets of stimulation are the thalamus, subthalamic nucleus, and the globus pallidus. The tip of the electrode is positioned within the targeted brain area and an extension wire is passed under the skin.
The third component, the neurostimulator, is implanted lower in the chest or under the skin over the abdomen. Ideally, electrical impulses are sent from the neurostimulator up along the extension wire and into the brain where they interfere with and block the electrical signals that cause Parkinson’s disease symptoms.