A 72-year-old woman from Bangalore presents with a 3-year history of progressive cognitive decline. Her daughter reports that she has experienced recurrent vivid visual hallucinations (seeing people and animals in her room), slow movement, and episodes of confusion that fluctuate throughout the day. On examination, she has a resting tremor, bradykinesia, and mild rigidity. Cognitive testing reveals impaired attention and executive function, with relatively preserved memory initially. MRI brain shows only mild generalized atrophy. What is the most likely diagnosis?

Explanation

## Diagnosis: Lewy Body Dementia (LBD) ### Core Clinical Features **Key Point:** Lewy body dementia is the second most common form of neurodegenerative dementia (after Alzheimer's). It is characterized by the pathological hallmark of Lewy bodies (alpha-synuclein inclusions) in the brain. ### Diagnostic Criteria for LBD (McKeith Criteria) **High-Yield: The "Core Features" of LBD:** 1. **Cognitive decline** — progressive, with early impairment of attention and executive function 2. **Visual hallucinations** — typically vivid, detailed, recurrent; often of people or animals 3. **Parkinsonism** — bradykinesia, rigidity, tremor (may be asymmetric) 4. **Fluctuating cognition** — significant day-to-day or hour-to-hour variation **Mnemonic: LBD = "Lewy bodies = Lucid hallucinations, Bradykinesia, Dementia with fluctuation"** ### Features Present in This Case - ✓ Vivid visual hallucinations (people, animals) - ✓ Parkinsonism (tremor, bradykinesia, rigidity) - ✓ Fluctuating confusion - ✓ Impaired attention and executive function - ✓ Relatively preserved memory initially - ✓ Minimal structural changes on MRI ### Differential Diagnosis | Feature | LBD | PDD | FTD-P | Alzheimer's | |---------|-----|-----|-------|-------------| | **Hallucinations** | Very common, vivid, early | Common, later | Rare | Uncommon | | **Parkinsonism** | Core feature, early | Follows cognitive decline | Can occur | Absent | | **Fluctuation** | Prominent | Mild | Absent | Absent | | **Atrophy on MRI** | Minimal, generalized | Mild | Anterior temporal/frontal | Hippocampal, temporal | | **Memory** | Relatively preserved early | Impaired | Preserved | Early and prominent | | **Attention/Executive** | Impaired early | Impaired | Impaired | Later impairment | | **Onset of parkinsonism** | Concurrent with/before dementia | After dementia (>1 yr) | Variable | Absent | **Clinical Pearl:** The **1-year rule** helps distinguish LBD from Parkinson's disease dementia (PDD): if parkinsonism precedes cognitive decline by >1 year, it is PDD; if cognitive decline and parkinsonism occur together or within 1 year, it is LBD. ### Why LBD, Not PDD? In this patient, cognitive decline and parkinsonism appear to have developed concurrently over 3 years, fitting the LBD timeline. PDD typically shows parkinsonism first (often for several years), followed by dementia. ### Pathophysiology **Key Point:** LBD is characterized by widespread Lewy bodies (alpha-synuclein inclusions) throughout the cortex and brainstem, leading to dopaminergic and cholinergic dysfunction. ### Clinical Management Implications **Warning:** Patients with LBD are exquisitely sensitive to antipsychotics (both typical and atypical), which can precipitate severe neuroleptic sensitivity reactions, including sudden worsening of parkinsonism, hyperthermia, and altered mental status. Avoid antipsychotics unless absolutely necessary; use non-pharmacological approaches first. **High-Yield:** Cholinesterase inhibitors (donepezil, rivastigmine) are effective for cognitive and behavioural symptoms in LBD and are first-line pharmacotherapy. ### Diagnostic Algorithm ```mermaid flowchart TD A[Dementia + parkinsonism]:::outcome --> B{Vivid visual hallucinations?}:::decision B -->|Yes| C{Fluctuating cognition?}:::decision C -->|Yes| D{Parkinsonism onset relative to dementia?}:::decision D -->|Concurrent or <1 yr apart| E[Lewy body dementia]:::outcome D -->|Parkinsonism >1 yr before dementia| F[Parkinson's disease dementia]:::outcome B -->|No| G{Anterior temporal atrophy?}:::decision G -->|Yes| H[FTD with parkinsonism]:::outcome G -->|No| I[Alzheimer's with extrapyramidal signs]:::outcome ``` [cite:Harrison 21e Ch 424; DSM-5 Major or Mild Neurocognitive Disorder Due to Lewy Body Disease]