The substantia nigra in the brain degenerates and fails to secrete sufficient levels of dopamine. These low levels of dopamine prevent normal transmission signals to the thalamus as well as the motor cortex. The mechanism of basal ganglia dysfunction or disruption is complex and eventual failure of compensatory mechanisms are often why symptoms worsen with disease progression.
This disease is most common in older patients and is the third most common neurological disorder in the US. It has an average age of onset of 60 years of age.
Cogwheel rigidity, also called hypokinesia or lead pipe rigidity, is seen in muscles of Parkinson's patients. When extending a limb like the arm, the muscles will exhibit a stop and go phenomenon.
Bradykinesia, or slow movements, are often seen in this disease. Patients will require more time to complete ADLs, like walking to the restroom, eating and bathing. Akinesia, or no movement, is seen in the later stages of the disease.
Classically patients with this disease have a shuffling or festinating gait. This is characterized by small steps which often involve shuffling of the feet. This gait appears because fine control of the muscles are lacking. Postural instability is also seen in many patients.
It is important to distinguish this disease from others because this tremor happens at rest. In normal patients, dopamine in the brain is constantly balanced to acetylcholine levels. When the dopamine levels decrease, acetylcholine is able to constantly stimulate small muscle contractions. This tremor will subside when the patient intentionally moves or is sleeping.
This tremor is classically described as "pill rolling," as if the patient were rolling a pill between their thumb and other fingers, as the tremor often affects the muscles of the thumb.
As muscles become rigid, patients develop a mask-like face, which is described as expressionless. Patients may experience other muscle difficulties of the face, including drooling and dysphagia.
Not all patients experience cognitive changes or dementia, which usually present later in the disease progression. However, patients will frequently experience mood lability and report sleep disturbances.
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