Neurological Disorders

A number of disorders affect primarily the peripheral neurological system of older adults. These include Parkinson's disease (PD), tardive dyskinesia (TD), spinocerebellar ataxias (SA), amyotropic lateral sclerosis (ALS), and progressive supranuclear palsy (PSP).

The major clinical features Parkinson's disease are bradykinesia (a slowness of movement), rigidity, and tremor at rest (experienced primarily in the hands). These symptoms emerge gradually. Older adults with PD also may have trouble with their balance, and so falls can become a concern. Depression is a frequent comorbid condition with PD. During the late stages of PD, memory impairment emerges as a prominent symptom, and the neuropathological correlates of this memory impairment are nearly identical to those of Alzheimer's disease. Onset before 30 years of age is rare, with the average age of onset being around 60 years. Nearly 1 person in 1,000 people develops PD during a given year among those 70 to 79 years of age. The lifetime risk is approximately 2.5%. Once the disease begins, people with the disease live approximately 15 years, but the life expectancy decreases with increased age of onset.

Classic PD is caused by degeneration of nerve cells in the base of the brain (the substantia nigra). These pigmented neurons produce dopamine and project this neurotransmitter to other parts of the brain, especially the striatum. Therefore, the main biochemical abnormality in PD is a marked deficiency of dopamine in the base of the brain. This leads to an imbalance between acetylcholine and dopamine in the striatum of the brain. Bradykinesia is the symptom of PD that is associated most closely with the loss of dopamine. Most cases of PD are sporadic, but PD has been linked to a mutation on chromosome 4. A number of medications can also cause Parkinson's-like symptoms. These especially include antipsychotic medications such as haloperidol. The frequency of PD-like symptoms is much lower with the new-generation antipsychotic drugs such as olanzapine and risperidone.

The primary treatment of PD is with medications. Anticholinergic drugs, such as trihexyphenidyl and benztropine, can be prescribed to correct the imbalance between acetylcholine and dopamine. The dopamine precursor levodopa is often prescribed in combination with carbidopa (Sinemet), which makes dopamine available to brain tissues. Bromocriptine and other drugs enhance the effectiveness of dopamine (they are dopamine agonists). Amantadine's mode of [Page 417]action is unknown, but it also enhances the effectiveness of dopamine. Selegiline is frequently used as an adjunct to Sinemet.

Tardive dyskinesia is one of the most serious side effects when using antipsychotic drugs, especially the older drugs such as thioridazine and haloperidol. The disorder manifests itself primarily with abnormal involuntary movements that typically involve the face initially (e.g., involuntary movements of the tongue) and then move to include the limbs and trunk. TD is much more common in the elderly taking these medications than in younger people. There is no known treatment. Withdrawal of the antipsychotic drug may increase the symptoms, but with time off the drug the symptoms can decrease. Switching to an atypical (new-generation) antipsychotic drug may improve symptoms, and beginning patients on these drugs, rather than the older drugs, reduces the risk.

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