A 58-year-old man from Delhi presents to the psychiatry outpatient clinic with a 2-year history of progressive personality change and socially inappropriate behaviour. His wife reports he has become disinhibited, making crude jokes in public and spending money recklessly. Cognitive testing shows relatively preserved memory and orientation, but he scores poorly on executive function tasks. Neuroimaging reveals marked anterior temporal lobe atrophy, more pronounced on the left. What is the most likely diagnosis?

Explanation

## Diagnosis: Behavioural Variant Frontotemporal Dementia (bvFTD) ### Clinical Presentation **Key Point:** Behavioural variant FTD is the most common form of frontotemporal dementia, accounting for 50–60% of FTD cases. It presents with early and prominent personality and behavioural changes rather than memory loss. ### Diagnostic Criteria Met 1. **Early behavioural change** — disinhibition, inappropriate social conduct, poor judgment 2. **Relative preservation of memory and orientation** — distinguishes from Alzheimer's disease 3. **Executive dysfunction** — poor performance on frontal lobe tasks 4. **Anterior temporal lobe atrophy** — characteristic neuroimaging finding, often left > right ### Key Distinguishing Features | Feature | bvFTD | Lewy Body | Alzheimer's | Vascular | |---------|-------|-----------|------------|----------| | **Early symptom** | Personality/behaviour | Visual hallucinations, parkinsonism | Memory loss | Stepwise decline | | **Memory** | Relatively preserved early | Preserved early | Early and prominent | Variable | | **Atrophy pattern** | Anterior temporal/frontal | Diffuse, minimal early | Hippocampal, temporal | Patchy, vascular distribution | | **Hallucinations** | Rare | Very common, vivid | Uncommon | Uncommon | | **Parkinsonism** | Absent | Present (core feature) | Absent | Absent | **High-Yield:** The triad of **disinhibition + executive dysfunction + anterior temporal atrophy** is pathognomonic for bvFTD. ### Pathology **Clinical Pearl:** bvFTD is associated with tau (Pick bodies) or TDP-43 pathology; Lewy body dementia is associated with alpha-synuclein. ### Diagnostic Algorithm ```mermaid flowchart TD A[Dementia presentation]:::outcome --> B{Memory loss prominent early?}:::decision B -->|Yes| C[Alzheimer's disease]:::outcome B -->|No| D{Visual hallucinations + parkinsonism?}:::decision D -->|Yes| E[Lewy body dementia]:::outcome D -->|No| F{Personality/behaviour change + executive dysfunction?}:::decision F -->|Yes| G{Anterior temporal atrophy on MRI?}:::decision G -->|Yes| H[Behavioural variant FTD]:::outcome G -->|No| I[Other FTD variant or vascular dementia]:::outcome ``` **Mnemonic: bvFTD = "Bad Behaviour, Frontal lobe, Temporal atrophy, Dementia"** [cite:Harrison 21e Ch 424]