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Parkinson disease (PD) also called Parkinson's disease, is a slow, progressive neurodegenerative disease of the extrapyramidal motor system for which there is presently no cure. The disorder results from the loss of nigrostriatal neurons in the substantia nigra pars compacta and Lewy body formation (misfolded proteins). By the time symptoms emerge and a diagnosis is made, it is estimated that 80% of nigrostriatal neurons have been lost. Due to a resultant deficiency in the neurotransmitter dopamine, there is less inhibitory output from the basal ganglia allowing for overactivity of acetylcholine. The neurotransmitter imbalance is responsible for the motor function abnormalities that characterize PD. The cardinal features of PD include tremor, bradykinesia, rigidity, and postural instability (though this symptom is rare in the early stages of the disease). PD symptoms typically begin unilaterally and spread to the opposite side as the disease progresses. Presentation varies among individuals and can differ substantially from person to person.

Tremor is the most common PD symptom, however, it is not universal. It may be described as a feeling of an internal vibration that is not outwardly apparent. Pill rolling (fingers and thumb moving in opposing directions) is a term used to describe the symptom. In mild disease, the tremor usually disappears with purposeful movement and during sleep. In some cases, tremor may also be present in the lips, chin, and jaw.

Bradykinesia (slow movement) may result in difficulty with tasks requiring repetitive movements and fine motor control (eg, teeth brushing). Arm swinging when walking may be diminished or absent and spontaneous gesturing and facial expression are often blunted. Shuffling gait may become apparent and difficulty turning in bed or rising from a chair may affect the patient's ability to function. Handwriting frequently becomes smaller (micrographia) and difficult to read. Eventually, all voluntary movement will be affected to some degree

Rigidity is resistance in the muscles upon initiation of passive movement and is described as “jerky” or “cogwheeling”. Vague muscle aches may be the first sign of rigidity and often occur in the back, shoulder, or arm. Some patients experience painful dystonias and cramping in the feet.

Postural instability (or postural reflex impairment) typically appears later in the disease process and is connected with advancing rigidity. Patients may be observed in a stooped position with flexion at the knees, hips, and waist. Patients may also be observed walking on the balls of their feet. Impairment of posture contributes substantially to the risk of injury secondary to falling.

PD is a diagnosis of exclusion. There are no biological or laboratory tests that can confirm PD (although a radiopharmaceutical indicated for striatal dopamine transporter visualization can be used to differentiate PD from other movement disorders). In general, if two of the cardinal features are present and characteristics of another movement disorder are absent, the diagnosis is made. A positive response to administration of ...

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