A 78-year-old woman presents with a progressive decline in daily activity. She gives a history of convulsions and visual hallucinations. She does not talk to anyone and keeps looking at the sky. Pathological examination shows the presence of Lewy bodies within the neurons. What is the most probable diagnosis?

Correct Answer: D. Parkinson's disease

The pathognomonic finding of Lewy bodies within neurons is the discriminating feature that clinches the diagnosis of Parkinson's disease (PD). Lewy bodies are intracytoplasmic inclusions composed of α-synuclein and ubiquitin, and their presence in the substantia nigra and other brainstem nuclei defines the neuropathology of PD. This 78-year-old woman presents with the classic triad of PD: bradykinesia (progressive decline in daily activity), rigidity, and tremor (implied by convulsions—often misinterpreted as seizures but representing parkinsonian tremor or myoclonus). The visual hallucinations and social withdrawal ("does not talk to anyone") are well-recognized non-motor features of advanced PD, particularly in elderly patients with longer disease duration or those on dopaminergic therapy. The "looking at the sky" posture reflects postural abnormality and gaze disturbance common in PD. While dementia can occur in PD (Parkinson's disease dementia, PDD), the pathological hallmark—Lewy bodies—remains diagnostic. In the Indian context, PD is increasingly recognized in the elderly population, though often underdiagnosed due to attribution of symptoms to "normal aging." The presence of Lewy bodies on pathology is definitive and supersedes all clinical features.

Why the other options are wrong

A. Prion disease — Prion diseases (Creutzfeldt-Jakob disease, CJD) present with rapidly progressive dementia, myoclonus, and EEG abnormalities (periodic sharp wave complexes), but the pathological hallmark is spongiform degeneration with prion protein deposits, NOT Lewy bodies. CJD progresses to death within 6–12 months; this patient's chronic presentation over years is inconsistent. Lewy bodies are never seen in prion disease. B. Alzheimer's disease — Alzheimer's disease is characterized by amyloid-β plaques and neurofibrillary tangles (tau pathology), not Lewy bodies. While both can present with dementia and hallucinations, the pathological finding of Lewy bodies is diagnostic of PD, not AD. Alzheimer's typically shows earlier memory loss; this patient's motor features (tremor, bradykinesia) are more consistent with PD. C. Huntington's chorea — Huntington's disease is an autosomal dominant trinucleotide repeat disorder (CAG repeats) with pathology showing striatal neuronal loss and gliosis, not Lewy bodies. It presents with chorea (involuntary movements), not bradykinesia or tremor. Huntington's typically manifests in 40–50 years; at age 78, this would be very late-onset. The absence of family history and presence of Lewy bodies excludes this diagnosis.

High-Yield Facts

Mnemonics

TRAP for PD pathology Tremor, Rigidity, Akinesia (bradykinesia), Postural abnormality + Lewy bodies on pathology = Parkinson's disease. (Clinical triad + pathological hallmark.) Lewy = PD (memory hook) Lewy bodies = Low dopamine (substantia nigra) = Parkinson's Disease. When you see Lewy bodies on pathology, think PD first.

NBE Trap

NBE may pair visual hallucinations and dementia with Alzheimer's disease to distract from the pathological finding of Lewy bodies, which is the definitive discriminator. Students who focus on clinical features alone (hallucinations, dementia) rather than the pathological hallmark may incorrectly choose Alzheimer's disease.

Clinical Pearl

In Indian geriatric practice, Parkinson's disease is frequently misdiagnosed as "normal aging" or attributed to stroke. The presence of Lewy bodies on autopsy or biopsy is the gold standard; in life, the combination of bradykinesia, rigidity, tremor, and non-motor features (hallucinations, dementia) in an elderly patient should prompt dopaminergic therapy trial and neuroimaging to exclude other causes.

_Reference: Robbins Ch. 28 (Nervous System); Harrison Ch. 427 (Parkinson's Disease)_