A 60-year-old woman presents with 6 months of asymmetric right-hand tremor, rigidity, and bradykinesia. She reports an excellent and sustained response to levodopa. Over the past 2 years she has developed visual hallucinations, fluctuating cognition, and parkinsonism. The dementia appeared within 1 year of motor symptoms. Which is the most likely diagnosis?
- A Idiopathic Parkinson's disease dementia
- B Alzheimer's disease with parkinsonism
- C Dementia with Lewy bodies ✓
- D Cortical basal degeneration
Correct answer: C. Dementia with Lewy bodies
Explanation
Dementia with Lewy bodies (DLB) is diagnosed when dementia occurs before or concurrently with (within 1 year of) parkinsonism. Core features include fluctuating cognition, recurrent visual hallucinations, and spontaneous parkinsonism. Parkinson's disease dementia is diagnosed when dementia occurs more than 1 year after well-established PD motor symptoms. This patient developed dementia within 1 year of motor symptoms, fitting DLB criteria. The 1-year rule is the key discriminator between DLB and PDD per consensus criteria.
Reference: Bradley's Neurology in Clinical Practice, 8th ed.
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