Degenerative Disorders of the Nervous System
QUICK LOOK AT THE CHAPTER AHEADParkinson’s disease is a common degenerative disorder of the basal ganglia involving the dopaminergic (dopamine-secreting) substantia nigra pathway. It is a slowly progressive disease generally diagnosed in late middle-aged and elderly persons. Parkinsonism is a term applied to the resulting movement disorders, such as poverty of movement, stiffness, tremors, and altered posture. Multiple sclerosis (MS) is a chronic progressive disease diffusely affecting neurons of the central nervous system. It is an acquired primary demyelinating disorder. Without myelin, nerve impulses slow down.
PARKINSON’S DISEASEParkinson’s disease is an idiopathic primary disease. Secondary parkinsonism is caused by disorders from trauma, postencephalitic parkinsonism infection, neoplasm, and toxins. Drug-induced parkinsonism is caused by some drugs such as reserpine, methyldopa, haloperidol, and phenothiazine and is usually reversible.
Parkinson’s disease is one of the most prevalent of the primary central nervous system problems and a major cause of disability in individuals over the age of 65. An estimated 500,000 individuals in the United States are affected. Men and women are affected equally. African Americans are rarely affected.
Pathophysiology
The pathology of Parkinson’s disease is associated with the loss of dopamine-producing cells in the substantia nigra in the midbrain, causing depletion of dopamine in the basal ganglia. The basal ganglia include the extrapyramidal system, which influences coordination, muscle tone, initiation, and completion of movement. It is thought that aging may predispose to this damage. A significant reduction in dopamine receptors in the basal ganglia has also been found. Dopamine is an inhibitory neurotransmitter that is necessary for the normal functioning of the extrapyramidal motor system. The depletion of dopaminergic activity leaves a relative excess of cholinergic activity. Acetylcholine is an excitatory neurotransmitter. It is postulated that an imbalance between inhibitory dopaminergic activity and excitatory cholinergic activity causes abnormalities in movement commonly associated with Parkinson’s disease.
The basal ganglia include the extrapyramidal system which influences coordination, muscle tone, initiation and completion of movement.Manifestations
The classic manifestations of Parkinson’s disease are tremors, rigidity, akinesia, and postural abnormalities. These manifestations may develop alone or in combination, but all four are usually present as the disease progresses. The onset of the disease is insidious, with a gradual progression and long course. It is usually 15 to 20 years before it produces invalidism. Cognitive-affective symptoms may also be a part of the disease and manifest as deterioration in memory or problem solving.
Initially, only a mild tremor, slight limp, and decreased arm swing may be evident. The tremor is usually the first manifestation. Initially, tremors are asymmetrical and later become symmetrical. They involve the arm more than the leg. The hand tremor is described as “pin rolling.” Tremors occur at rest, disappear with movement, and are aggravated with stress.
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