Pathophysiology of Parkinsonism and Chorea

Parkinsonism: Core Pathophysiological Mechanisms

Parkinsonism results from degeneration of dopaminergic neurons in the substantia nigra pars compacta, leading to striatal dopamine deficiency that disrupts the basal ganglia-thalamo-cortical circuit, with symptoms manifesting after approximately 40-50% neuronal loss 1
Alpha-synuclein aggregation forms the pathological hallmark, with abnormal cytoplasmic inclusions (Lewy bodies) accumulating in neurons, classifying Parkinson's disease as a synucleinopathy 1
Mitochondrial dysfunction, particularly decreased Complex I activity in the respiratory chain, drives progressive neurodegeneration 1
Cardinal motor symptoms include bradykinesia (essential for diagnosis), rigidity, resting tremor (4-6 Hz "pill-rolling"), and postural instability, all resulting from striatal dopamine deficiency 1, 2, 3
Symptoms typically appear 5 years after initial neurodegeneration begins, when 40-50% of dopaminergic neurons have been lost 1, 3

Both conditions involve abnormal basal ganglia-thalamo-cortical circuit function but represent opposite ends of the movement disorder spectrum 4, 5