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A reduction or absence of psychomotor activity that results in a masklike facial expression and impaired postural reflexes. A classic characteristic of Parkinson's disease.


Slowness of movement; another classic symptom of Parkinson's disease.


A condition characterized by involuntary, purposeless, rapid motions such as flexing and extending the fingers, raising and lowering the shoulders, or grimacing.


An impaired ability to execute voluntary movements.


Impaired or distorted voluntary movement due to a disorder of muscle tone.


A term describing any substance produced outside of the body that may be taken into the body (e.g. medication, food, or environmental toxin).

On-off phenomenon

A common experience of patients taking medication for Parkinson's disease in which they experience periods of greater symptomatic control ("on" time) altering with periods of lesser symptomatic control ("off" time).

Parkinson's disease

A slowly progressive, degenerative neurologic disorder characterized by resting tremor, pill-rolling of the fingers, masklike facies, shuffling gait, forward flexion of the trunk, loss of postural reflexes, and muscle rigidity and weakness.

Postural instability

A decrease or change in motor or muscle movements that leads to unsteadiness and hesitation in movement and gait when the individual starts or stops walking; occurs in Parkinson's disease.


Drugs that exert their antiparkinsonian effects before the nerve synapse.


Resistance of the muscles to passive movement; leads to the "cogwheel" rigidity seen in Parkinson's disease.


In Parkinson's disease, shakiness of the extremitites seen mostly at rest.

Wearing off phenomenon

A gradual worsening of Parkinsonian symptoms as a patient's medications begin to lose their effectiveness, despite maximal dosing with a variety of medications.

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