Parkinson's disease (PD) is a chronic, progressive neurodegenerative condition caused by lack of dopamine in the brain, due to loss of the dopamine-containing cells of the substantia nigra.

PD is a movement disorder with four core features: tremor (shaking), bradykinesia (slowness of movement), rigidity (muscle stiffness) and postural instability (difficulty with balance and coordination).

NICE CKS - Parkinson's disease

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