A 58-year-old man from Delhi presents with a 2-year history of progressive personality change and socially inappropriate behaviour. His wife reports he has become disinhibited, making crude jokes at family gatherings, and has lost interest in his accounting job despite being previously meticulous. He occasionally forgets recent conversations but can recall distant memories clearly. On examination, he is alert and oriented but shows poor impulse control. Mini-Cog score is 24/30. MRI brain shows selective atrophy of the anterior temporal lobes bilaterally. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Behavioural Variant Frontotemporal Dementia (bvFTD) ### Key Clinical Features Pointing to bvFTD **Key Point:** The hallmark of behavioural variant FTD is *early and prominent personality change and social disinhibition* with *preserved episodic memory* in the initial stages — exactly what this patient demonstrates. ### Diagnostic Criteria Met | Feature | Present in Case | Significance | |---------|-----------------|-------------| | Age of onset | 58 years (< 65) | FTD typically younger than AD | | Early personality change | Yes (disinhibition, crude behaviour) | Core feature of bvFTD | | Social inappropriateness | Yes (crude jokes, loss of decorum) | Reflects orbitofrontal/ventromedial PFC pathology | | Preserved episodic memory | Yes (recalls distant memories, forgets recent conversations) | Distinguishes from AD (which has early amnesia) | | Anterior temporal lobe atrophy | Yes, bilateral | Pathognomonic for bvFTD | | Relatively preserved cognition | MMSE-equivalent 24/30 | Early-stage FTD may spare global cognition | ### Pathophysiology 1. **Orbitofrontal and ventromedial prefrontal cortex involvement** → loss of social inhibition, impulsivity, poor decision-making 2. **Anterior insula and anterior cingulate atrophy** → emotional blunting, apathy 3. **Relative sparing of posterior cortex and hippocampus** → memory relatively preserved early **High-Yield:** The *dissociation between preserved memory and impaired behaviour* is the clinical signature of bvFTD and distinguishes it from Alzheimer disease. ### Neuropathology - **Pick bodies** (tau inclusions) or **TDP-43 inclusions** (most common) - Loss of neurons in frontal and temporal poles - Gliosis and spongiosis **Clinical Pearl:** FTD patients often present to psychiatry first (misdiagnosed as personality disorder or depression) because behavioural symptoms dominate early; cognitive decline comes later. ### Diagnostic Criteria (International Consensus) BvFTD requires: - Insidious onset and gradual progression - Early behavioural disinhibition OR apathy/inertia - Loss of empathy - Preserved episodic memory (initially) - Structural imaging showing frontal/anterior temporal atrophy **Mnemonic: DISINHIBIT** — **D**isinhibition, **I**nappropriate behaviour, **S**ocial decline, **I**mpulsivity, **N**eurodegeneration (frontal), **H**yperoral/eating changes, **I**nertia/apathy, **B**ehavioural rigidity, **I**nsidious onset, **T**emporal/frontal atrophy.