Educational scope notice: This is a study note for medical students, not medical advice, diagnosis, or treatment guidance. Clinical management should follow local protocols and current guidelines.
Frontotemporal dementia is the dementia of younger patients, typically striking between 50 and 65. The first symptom is behavioural change or language loss, not memory loss. A middle-aged patient who stops paying bills, loses motivation, and starts making inappropriate jokes points toward frontotemporal dementia; one who cannot remember yesterday points toward Alzheimer disease.
Behavioural variant
Personality change dominates while memory stays relatively intact: the patient forgets nothing but no longer cares. Damage to frontal control circuits produces disinhibition (inappropriate jokes and socially unrestrained acts), apathy (flat affect, loss of drive, easily mistaken for depression), loss of social norms without embarrassment, and executive failure with planning and finances. Insight is lost early.
Language variants
The nonfluent variant is a production problem: effortful, halting speech with word-finding difficulty and grammar errors, while comprehension and memory of events stay intact. MRI shows left frontal and insular atrophy in the speech-planning areas.
The semantic variant is a meaning problem: speech stays fluent but words lose meaning, with prominent difficulty naming objects and understanding names offered. MRI shows anterior temporal atrophy, usually left-sided, in the hub where conceptual knowledge is stored.
A right temporal presentation causes progressive loss of face recognition with behavioural disturbance: the mirror image of losing word meaning.
Genetics and protein pathology
Frontotemporal dementia has a strong familial thread. The main pathological groups are tau deposition (including Pick bodies with MAPT mutations), TDP-43 deposition (including C9orf72 repeat expansions and progranulin mutations), and rare FUS deposition. The C9orf72 expansion is the most common genetic cause of familial disease and the bridge to motor neuron disease: about 15–20% of frontotemporal dementia patients have an associated motor neuron disease, so progressive weakness or fasciculations in a dementia patient should raise this link.
Frontotemporal versus Alzheimer dementia at the bedside
| Feature | Frontotemporal dementia | Alzheimer disease |
|---|---|---|
| Onset age | 50–65 | Usually over 70 |
| First symptom | Personality or language change | Memory loss |
| Memory | Preserved early | Lost early |
| Insight | Lost early | Preserved longer |
| Behaviour | Disrupted early | Disrupted later |
| MRI pattern | Frontal and temporal atrophy | Temporal and parietal atrophy |
FDG-PET follows the same split when MRI is equivocal: frontal and anterior temporal hypometabolism in frontotemporal dementia versus temporoparietal hypometabolism in Alzheimer disease.
Evidence anchors
- NICE. Dementia: assessment, management and support (NG97): https://www.nice.org.uk/guidance/ng97