A 72-year-old woman from Mumbai presents with a 2-year history of progressive behavioral changes. Her family reports she has become socially inappropriate, disinhibited, and emotionally blunted. She frequently uses profanities and makes crude jokes. Memory is relatively preserved early on, though she is now developing some forgetfulness. She shows poor judgment and has spent large sums on unnecessary items. On examination, she has hyperreflexia and an exaggerated jaw jerk. MRI shows marked frontal and anterior temporal lobe atrophy with relative sparing of the hippocampus. Which is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Behavioral-Variant Frontotemporal Dementia (bvFTD) ### Distinguishing Features of bvFTD **Key Point:** Behavioral-variant FTD is characterized by early behavioral/personality changes with relative preservation of memory and visuospatial function — the opposite of Alzheimer's disease. ### Clinical Presentation Comparison | Feature | bvFTD | Alzheimer's Disease | Lewy Body Dementia | |---------|-------|-------------------|-------------------| | **First symptom** | Behavioral change, apathy | Memory loss | Fluctuation, hallucinations | | **Memory early** | Relatively preserved | Impaired early | Impaired | | **Personality** | Disinhibition, inappropriate | Preserved early | Preserved | | **Judgment** | Severely impaired | Preserved early | Preserved early | | **Atrophy pattern** | Frontal > temporal | Hippocampal, temporal-parietal | Diffuse | | **Hyperreflexia/jaw jerk** | Common (motor neuron signs) | Absent | Absent | | **Hallucinations** | Rare | Rare | Frequent | ### Pathological Hallmarks of bvFTD **High-Yield:** bvFTD is part of the **frontotemporal dementia spectrum**, which includes: 1. **Behavioral-variant FTD** (this case) — behavioral/personality changes 2. **Semantic dementia** — word meaning loss, anomia 3. **Nonfluent/agrammatic PPA** — speech production difficulty 4. **Corticobasal syndrome** — asymmetric motor signs 5. **Progressive supranuclear palsy** — vertical gaze palsy, falls All share **frontotemporal atrophy** on imaging and **TDP-43 or tau pathology** on neuropathology. ### Diagnostic Criteria for bvFTD **Mnemonic: "DISINHIBIT" for behavioral-variant FTD:** - **D**isinhibition (socially inappropriate, impulsive) - **I**napathy (emotional blunting, lack of empathy) - **S**ocial withdrawal or inappropriate behavior - **I**mpulsivity (poor judgment, risky decisions) - **N**europsychiatric symptoms (aggression, irritability) - **H**yperoral behavior (overeating, dietary changes) - **I**nability to recognize emotions in others - **B**ehavioral rigidity and perseveration - **I**ncreased spending/poor financial judgment - **T**emporal lobe atrophy on imaging ### Motor Signs in bvFTD **Clinical Pearl:** Hyperreflexia, exaggerated jaw jerk, and increased tone suggest **upper motor neuron signs** — these are common in bvFTD due to involvement of motor cortex and corticospinal tract. Some patients progress to **primary lateral sclerosis (PLS)** or **amyotrophic lateral sclerosis (ALS)**. ### Neuroimaging Pattern **Key Point:** The **frontal and anterior temporal atrophy with relative sparing of hippocampus** is pathognomonic for bvFTD and distinguishes it from Alzheimer's disease (which shows hippocampal atrophy). ### Why Memory Is Preserved Early in bvFTD The **hippocampus and medial temporal lobes** (critical for memory) are relatively spared in bvFTD. Atrophy is concentrated in the **prefrontal cortex** (behavior, judgment, emotion) and **anterior insula** (empathy, social cognition). [cite:Harrison 21e Ch 424; Robbins 10e Ch 28]