Final answer:
The neuropathological hallmark of idiopathic Parkinson's disease is Brain-stem Lewy bodies, which are protein aggregates found in the dopaminergic neurons and correlate with disease severity.
Step-by-step explanation:
The neuropathological hallmark of idiopathic Parkinson's disease is A. Brain-stem Lewy bodies. Parkinson's disease, a neurodegenerative disorder, causes the loss of dopaminergic neurons in the substantia nigra, a midbrain structure critical for movement regulation. This neuronal loss manifests through various symptoms including tremors, rigidity, and bradykinesia. The protein aggregates named Lewy bodies, composed mainly of alpha-synuclein, are commonly found in the brains of those with Parkinson's disease, and their presence correlates with the severity of the disease. These Lewy bodies, coupled with mitochondrial dysfunction and oxidative stress, contribute to the neuronal degeneration observed in Parkinson's disease.