1. Overview
As early as 1877, Jean-Martin Charcot described cognitive and personality changes in Parkinson’s disease (PD) patients. However, Parkinson’s disease dementia (PDD) gained significant attention only in the 1960s. Studies indicate that 24–31% of PD patients develop PDD, with 70–80% of PD patients eventually progressing to PDD. PDD accounts for 3–4% of all dementia cases, and approximately 10% of PD patients transition to PDD annually. PDD severely impacts social functioning and quality of life in the elderly.
Clinical Features of PDD
1. Extrapyramidal Symptoms
- Characteristics:
- Dominated by axial symptoms (e.g., postural instability, gait disturbances).
- Tremor is less common, possibly due to dysfunction in non-dopaminergic pathways.
- Poor response to levodopa therapy, reflecting multisystem neurodegeneration.
2. Cognitive Impairment
PDD manifests as subcortical dementia in early/moderate stages, progressing to mixed subcortical-cortical dementia in advanced stages. Deficits involve:
- Attention Deficits (29% of patients):
- Fluctuating attention, reduced alertness, and impaired focus.
- Assessment:
- Serial subtraction of 7 from 100 (≥2 errors).
- Reverse recitation of months (errors or >90 seconds to complete).
- Executive Dysfunction:
- Impaired planning, task-switching, and problem-solving.
- Assessment:
- Verbal fluency: <11 animals named in 1 minute.
- Clock-drawing test: Errors in numbering or time indication (e.g., 11:10).
- Visuospatial Impairment:
- Difficulty with object recognition, shape discrimination, and figure copying.
- Assessment: Figure-copying tasks in the Mini-Mental State Examination (MMSE).
- Memory Loss:
- Retrieval-based deficits: Impaired recall despite intact encoding/storage (cues improve performance).
- Assessment:
- MMSE: Failure to recall 3 items (e.g., “ball, flag, tree”) after 3–5 minutes.
- Montreal Cognitive Assessment (MoCA): Delayed recall score ≤3/5; preserved recognition with cues.
3. Neuropsychiatric Symptoms
- Common: Visual hallucinations, illusions, delusions, depression, apathy, and REM sleep behavior disorder.
- Note: Depression may confound cognitive assessments; treat depression first before reevaluating cognition.
Key Diagnostic Tools
- MMSE: Evaluates attention, memory, and visuospatial skills.
- MoCA: Assesses executive function, delayed recall, and orientation.
- Neuropsychiatric Inventory (NPI): Screens for hallucinations, depression, and sleep disturbances.
Clinical Pearls
- Early PDD: Subcortical deficits (executive dysfunction, slowed processing).
- Advanced PDD: Mixed cortical-subcortical features (aphasia, agnosia).
- Treatment: Cholinesterase inhibitors (e.g., rivastigmine) for cognitive/behavioral symptoms; address psychosis with cautious use of antipsychotics (e.g., quetiapine).
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