Neuropathological Finding in Parkinson's Disease
The postmortem histopathologic examination will most likely reveal intracytoplasmic eosinophilic inclusions composed of alpha-synuclein in pigmented neurons in the brainstem (substantia nigra). 1, 2
Clinical Presentation Confirms Parkinson's Disease
This patient presents with the classic triad of Parkinson's disease:
- Resting tremor that is more prominent when distracted 1, 3
- Cogwheel rigidity in the right wrist 3, 2
- Asymmetric presentation (right-sided predominance), which is characteristic of idiopathic Parkinson's disease 1
The American College of Radiology confirms that these cardinal features—resting tremor, rigidity, and bradykinesia—are the hallmark clinical presentation of Parkinson's disease. 1
Pathological Correlate
The defining neuropathological features of Parkinson's disease are:
- Degeneration of dopaminergic neurons in the substantia nigra pars compacta projecting to the striatum 1, 2, 4
- Lewy bodies: intracytoplasmic eosinophilic inclusions composed of aggregated alpha-synuclein protein in pigmented neurons of the brainstem, particularly the substantia nigra 2, 5, 4
The American College of Radiology states that symptoms manifest after approximately 40-50% of dopaminergic neurons have been lost, which explains this patient's one-year progression of symptoms. 1, 3
Why Other Options Are Incorrect
Extracellular amyloid beta aggregates throughout the cerebral cortex would indicate Alzheimer's disease pathology, not Parkinson's disease. 6 The National Institute on Aging-Alzheimer's Association guidelines specify that extracellular amyloid plaques and neurofibrillary tangles are the essential neuropathologic features of Alzheimer's disease, not the parkinsonian syndrome this patient exhibits. 6
Intracytoplasmic inclusions composed of tau in neurons of the temporal lobes would suggest frontotemporal dementia or other tauopathies. 6 The American College of Radiology notes that frontotemporal lobe degeneration is associated with frontotemporal dementia rather than classic parkinsonian symptoms. 1
Intracytoplasmic eosinophilic inclusions composed of actin in neurons within the hippocampal formation is not a recognized pathological finding in any major neurodegenerative disease. 6
Disease Progression Pattern
The American College of Radiology describes that Lewy body deposition in Parkinson's disease follows a characteristic pattern:
- Initially affects the medulla oblongata, pontine tegmentum, and olfactory system 1, 5
- Subsequently involves the substantia nigra and other deep gray nuclei 1, 5
- In later stages (Lewy body dementia), spreads to cortical regions 7, 8
This patient's presentation with predominantly motor symptoms without cognitive impairment suggests early-stage disease with pathology primarily localized to the brainstem, specifically the substantia nigra. 1, 4
Clinical Pitfall to Avoid
Do not confuse the target structures (caudate and putamen) that receive projections from the substantia nigra with the primary site of neuronal degeneration (substantia nigra pars compacta). 1 The striatum shows dopaminergic denervation as a consequence of substantia nigra degeneration, but the pathognomonic Lewy bodies are found in the pigmented neurons of the substantia nigra. 2, 4