Although the cause of Parkinson’s disease is unknown, study of the extrapyramidal brain nuclei (corpus striatum, globus pallidus, substantia nigra) has established that a dopamine deficiency prevents affected brain cells from performing their normal inhibitory function within the central nervous system.

The cardinal signs and symptoms of Parkinson’s disease are muscle rigidity, bradykinesia or akinesia, loss of position sense with postural instability, and an insidious tremor that begins in the fingers (unilateral pill-roll tremor), increases during stress or anxiety, and decreases with purposeful movement and sleep.

Muscle rigidity results in resistance to passive muscle stretching, which may be uniform (lead-pipe rigidity) or jerky (cogwheel rigidity). Akinesia causes the patient to walk with difficulty
(gait lacks normal parallel motion and may be retropulsive or propulsive).

Parkinson’s disease also produces a high-pitched, monotone voice; drooling; a masklike facial expression; loss of posture control (the patient walks with body bent forward); and dysarthria, dysphagia, or both. Occasionally, akinesia may also cause oculogyric crises (eyes are fixed upward, with involuntary tonic movements) or blepharospasm (eyelids are completely closed).

Parkinson’s disease results in dementia in about 10% of those diagnosed. Theorists believe this may be due to the advanged age of some patients or a coexisting disorder such as arteriosclerosis that results in cognitive deficits.