Frontotemporal Dementia
Frontotemporal Dementia
What Do You Need to Know?
- Second most common early-onset dementia (after AD) — typical onset age 45–65; equal sex distribution
- Three clinical syndromes: behavioral variant FTD (bvFTD), nonfluent/agrammatic PPA (nfvPPA), and semantic variant PPA (svPPA); logopenic PPA (lvPPA) is usually AD pathology
- Behavioral variant hallmarks: early disinhibition, apathy, loss of empathy, compulsive behaviors, hyperorality, executive dysfunction with relative sparing of episodic memory and visuospatial function
- Genetics: ~30–50% have autosomal dominant family history; C9orf72 hexanucleotide repeat is the most common genetic cause and links FTD to ALS
- Neuropathology classified by protein inclusion — FTLD-tau (Pick bodies, PSP, CBD), FTLD-TDP (types A–E), FTLD-FUS — NOT by clinical syndrome
- No disease-modifying therapy: SSRIs and trazodone for behavioral symptoms; avoid cholinesterase inhibitors (may worsen bvFTD behavior)
- Key differentiator from AD: personality/behavioral change precedes memory loss; frontal > temporal atrophy; younger age at onset
FTD Spectrum Overview
Key Epidemiologic and Clinical Features
- Prevalence: 15–22 per 100,000 in those aged 45–65; second only to AD in early-onset dementia
- Mean age of onset: ~58 years (range 21–85, but most 45–65)
- Equal sex distribution (unlike AD, which is more common in women)
- Mean survival: 6–8 years from symptom onset (shorter with concomitant ALS: 2–3 years)
- Most patients initially misdiagnosed as psychiatric illness (depression, bipolar, personality disorder) due to prominent behavioral changes
Clinical Spectrum
| Syndrome | Core Feature | Atrophy Pattern | Common Pathology |
|---|---|---|---|
| bvFTD | Behavioral/personality change | Frontal > temporal (bilateral, often asymmetric) | ~50% tau, ~50% TDP-43 |
| nfvPPA | Effortful, agrammatic speech | Left posterior frontal / insular | Usually tau (4R: CBD or PSP pathology) |
| svPPA | Loss of word/object meaning | Left anterior temporal | Usually TDP-43 (type C) |
| lvPPA | Word-finding difficulty, impaired repetition | Left posterior temporal / inferior parietal | Usually AD pathology (amyloid+) |
💎 Board Pearl
- lvPPA is the outlier — despite being classified as a PPA variant, the underlying pathology is usually Alzheimer disease (amyloid-positive), NOT FTLD. This is a favorite board question
- bvFTD is the most common FTD variant — accounts for ~60% of all FTD cases
Behavioral Variant FTD (bvFTD)
Rascovsky Diagnostic Criteria (2011)
- Requires ≥3 of 6 core features for possible bvFTD
- Probable bvFTD: possible criteria + functional decline + characteristic neuroimaging (frontal/anterior temporal atrophy or hypoperfusion/hypometabolism)
- Definite bvFTD: probable criteria + histopathologic confirmation or known pathogenic mutation
| Core Feature | Examples / Details |
|---|---|
| 1. Early behavioral disinhibition | Socially inappropriate behavior, loss of manners/decorum, impulsive/reckless actions |
| 2. Early apathy/inertia | Loss of motivation, initiative, and interest; often misdiagnosed as depression |
| 3. Early loss of sympathy/empathy | Diminished response to others’ needs/feelings; social coldness |
| 4. Perseverative/compulsive behaviors | Simple repetitive movements, hoarding, ritualistic behavior, stereotypies |
| 5. Hyperorality/dietary changes | Binge eating, carbohydrate craving, oral exploration of inedible objects, increased alcohol/tobacco use |
| 6. Executive dysfunction with relative sparing of memory and visuospatial function | Impaired planning, abstraction, mental flexibility; episodic memory and visuospatial skills relatively preserved early |
Clinical Features by Frontal Subregion
| Predominant Atrophy | Clinical Presentation |
|---|---|
| Orbitofrontal / ventromedial | Disinhibition, impulsivity, sociopathic behavior, poor judgment |
| Dorsolateral prefrontal | Executive dysfunction, poor planning, perseveration |
| Anterior cingulate / medial frontal | Apathy, abulia, loss of motivation |
| Right temporal predominant | Behavioral changes + prosopagnosia, loss of person-specific knowledge |
💎 Board Pearl
- Apathy is the most common symptom of bvFTD — more common than disinhibition, but disinhibition is more distinctive and recognizable
- “Sweet tooth” and carbohydrate craving are classic bvFTD features — ask about dietary changes in every suspected case
- Memory can be impaired in bvFTD but it is a retrieval deficit (improves with cueing), unlike the encoding deficit in AD (does not improve with cueing)
Primary Progressive Aphasia (PPA) Variants
PPA Diagnostic Framework
- Core PPA criteria (Mesulam): insidious onset, gradual progression of language as the most prominent clinical feature for ≥2 years
- Other cognitive domains relatively spared initially
- Three variants classified by pattern of language deficits, each mapping to distinct atrophy and pathology
Nonfluent/Agrammatic Variant PPA (nfvPPA)
Core Features (at least 1 of 2 required)
- Agrammatism in language production — short, telegraphic sentences; omission of function words and grammatical morphemes
- Effortful, halting speech with apraxia of speech (AOS) — inconsistent speech sound errors, distortions, groping
Supporting Features (≥2 of 3)
- Impaired comprehension of syntactically complex sentences
- Spared single-word comprehension
- Spared object knowledge
Key Points
- Atrophy: left posterior frontal (inferior frontal gyrus / Broca area) and insular cortex
- Pathology: usually FTLD-tau (4R tau — CBD or PSP pathology)
- May evolve into CBD or PSP clinically over time
Semantic Variant PPA (svPPA)
Core Features (both required)
- Impaired confrontation naming
- Impaired single-word comprehension — loss of word meaning (“What is a fork?”)
Supporting Features (≥3 of 4)
- Impaired object knowledge (especially for low-frequency/low-familiarity items)
- Surface dyslexia/dysgraphia — regularization errors (e.g., “yacht” read as “yatcht”)
- Spared repetition
- Spared speech production (fluent, grammatically correct but “empty”)
Key Points
- Atrophy: left anterior temporal lobe (temporal pole, fusiform, inferior/middle temporal gyri) — “knife-edge” temporal atrophy
- Pathology: usually FTLD-TDP-43 (type C)
- Right temporal variant → prosopagnosia, loss of person-specific knowledge, behavioral changes
Logopenic Variant PPA (lvPPA)
Core Features (both required)
- Impaired single-word retrieval in spontaneous speech and naming
- Impaired sentence/phrase repetition
Supporting Features (≥3 of 4)
- Phonological errors in spontaneous speech and naming
- Spared single-word comprehension and object knowledge
- Spared motor speech (no AOS)
- Absence of frank agrammatism
Key Points
- Atrophy: left posterior temporal and inferior parietal cortex (temporoparietal junction)
- Pathology: usually Alzheimer disease (amyloid and tau) — NOT FTLD
- Amyloid PET typically positive; responds to cholinesterase inhibitors (unlike bvFTD and other PPAs)
PPA Variant Comparison
| Feature | nfvPPA | svPPA | lvPPA |
|---|---|---|---|
| Fluency | Nonfluent, effortful | Fluent but empty | Fluent with frequent pauses |
| Grammar | Agrammatic | Preserved | Preserved |
| Naming | Relatively preserved early | Severely impaired | Impaired |
| Single-word comprehension | Preserved | Impaired | Preserved |
| Repetition | Relatively preserved | Preserved | Impaired |
| Motor speech | AOS present | Normal | Normal |
| Reading | Preserved early | Surface dyslexia | Phonological errors |
| Atrophy | Left posterior frontal/insula | Left anterior temporal | Left posterior temporal/parietal |
| Usual pathology | FTLD-tau (4R) | FTLD-TDP (type C) | Alzheimer disease |
💎 Board Pearl
- Surface dyslexia = svPPA — regularization errors on irregular words (e.g., “pint” rhymed with “mint”) are pathognomonic for loss of semantic word knowledge
- Impaired repetition is the hallmark of lvPPA and distinguishes it from the other two variants. Think “logopenic = lost repetition = likely AD”
- nfvPPA + parkinsonism = think CBD or PSP — nonfluent aphasia is the most common cortical presentation of corticobasal pathology
Genetics of FTD
Overview
- ~30–50% of FTD patients have a positive family history; ~10–25% have an identifiable autosomal dominant mutation
- FTD is the most heritable of all common dementias
- Three major genes account for the vast majority of familial FTD
Major FTD Genes
| Gene | Chromosome | Protein / Pathology | Key Features |
|---|---|---|---|
| C9orf72 | 9p21 | GGGGCC hexanucleotide repeat expansion → FTLD-TDP (type A or B), dipeptide repeat (DPR) inclusions | Most common genetic cause of FTD AND ALS; FTD-ALS spectrum; psychosis and hallucinations more common; variable penetrance; repeat ≥30 = pathogenic |
| GRN (progranulin) | 17q21 | Haploinsufficiency → FTLD-TDP (type A) | Highly variable phenotype even within families; asymmetric atrophy; plasma progranulin levels low (screening test); may present as CBS or nfvPPA |
| MAPT (microtubule-associated protein tau) | 17q21 | Abnormal tau → FTLD-tau (3R, 4R, or mixed) | bvFTD phenotype most common; parkinsonism frequent; symmetric temporal atrophy; original “FTDP-17” families |
Less Common Genes
- VCP (valosin-containing protein) — inclusion body myopathy + Paget disease + FTD (IBMPFD); FTLD-TDP
- CHMP2B — rare; Danish kindred; FTLD-UPS
- TBK1 — FTD-ALS spectrum; FTLD-TDP
- TARDBP, FUS — primarily ALS genes, occasionally FTD
💎 Board Pearl
- C9orf72 is the #1 genetic cause of both FTD and familial ALS — a single gene linking two diseases. Up to 25% of familial FTD and 40% of familial ALS carry this mutation
- Both GRN and MAPT are on chromosome 17 but produce completely different pathologies: GRN → TDP-43 inclusions; MAPT → tau inclusions
- Low plasma progranulin level is a biomarker for GRN mutations — useful screening test before genetic sequencing
Neuropathology
FTLD Classification by Protein Inclusion
- Clinical syndrome does NOT reliably predict underlying pathology — classification is based on the abnormal protein found at autopsy
- Two main categories: FTLD-tau (~40%) and FTLD-TDP (~50%); FTLD-FUS (~5–10%)
| Pathologic Category | Subtypes | Key Histologic Features | Associated Clinical Syndromes |
|---|---|---|---|
| FTLD-tau (3R tau) | Pick disease | Pick bodies — round, intracytoplasmic, argyrophilic, 3R tau-positive inclusions; ballooned neurons (Pick cells); severe frontal/temporal atrophy | bvFTD, svPPA |
| FTLD-tau (4R tau) | PSP, CBD, GGT, AGD | PSP: tufted astrocytes, globose tangles; CBD: astrocytic plaques, ballooned neurons; both 4R tau-predominant | PSP syndrome, CBS, nfvPPA, bvFTD |
| FTLD-TDP | Types A–E | TDP-43-positive neuronal cytoplasmic inclusions (NCI) and/or dystrophic neurites (DN) and/or neuronal intranuclear inclusions (NII) | bvFTD, svPPA (type C), FTD-ALS (type B), nfvPPA |
| FTLD-FUS | aFTLD-U, NIFID, BIBD | FUS-positive inclusions; basophilic inclusions in BIBD | bvFTD (especially young-onset, severe behavioral changes) |
TDP-43 Subtypes
| TDP-43 Type | Pathologic Pattern | Genetic Association | Clinical Correlation |
|---|---|---|---|
| Type A | Many NCI + DN + frequent NII | GRN mutations; C9orf72 | bvFTD, nfvPPA |
| Type B | Many NCI, sparse DN, no NII | C9orf72 | FTD-ALS, bvFTD |
| Type C | Many long DN, sparse NCI | Usually sporadic | svPPA |
| Type D | Many NII + DN | VCP mutations | IBMPFD |
| Type E | Granulofilamentous NCI, widespread | Sporadic | Rapidly progressive FTD |
💎 Board Pearl
- Pick bodies = 3R tau, Pick disease — round, silver-staining, intracytoplasmic inclusions. The classic FTLD-tau entity
- Tufted astrocytes = PSP; astrocytic plaques = CBD — glial tau morphology distinguishes 4R tauopathies on pathology
- Clinical syndrome does NOT predict pathology — bvFTD can be tau, TDP-43, or FUS. Pathologic classification requires autopsy or biomarkers
Overlap Syndromes
FTD-ALS (FTD–Motor Neuron Disease)
- ~15% of FTD patients develop ALS; ~15% of ALS patients develop FTD — a clinical and pathologic continuum
- C9orf72 hexanucleotide repeat is the most common genetic link between FTD and ALS
- TDP-43 type B pathology is the most common neuropathologic substrate
- Concomitant ALS dramatically shortens survival (2–3 years vs. 6–8 years for FTD alone)
- All FTD patients should be screened for upper and lower motor neuron signs at every visit
Progressive Supranuclear Palsy (PSP)
- 4R tauopathy; vertical supranuclear gaze palsy (downgaze > upgaze), axial rigidity, early falls (backward), frontal cognitive dysfunction
- PSP may present as bvFTD or nfvPPA (PSP-frontal or PSP-SL variant)
- Midbrain atrophy on MRI (“hummingbird sign” sagittal; “morning glory sign” axial)
Corticobasal Syndrome / Corticobasal Degeneration
- 4R tauopathy (pathologic diagnosis = CBD); clinical syndrome (CBS) can result from multiple pathologies (CBD, AD, PSP, TDP-43)
- Asymmetric limb rigidity, apraxia, cortical sensory loss, alien limb phenomenon, myoclonus
- CBS may present with nfvPPA, bvFTD, or posterior cortical atrophy phenotypes
- Asymmetric frontoparietal atrophy on MRI
| Feature | FTD-ALS | PSP | CBS/CBD |
|---|---|---|---|
| Key mutation | C9orf72 | MAPT (rare) | MAPT (rare) |
| Pathology | FTLD-TDP (type B) | 4R tau (tufted astrocytes) | 4R tau (astrocytic plaques) |
| Distinguishing sign | UMN + LMN signs | Vertical gaze palsy, early falls | Alien limb, asymmetric apraxia |
| Imaging hallmark | Frontotemporal atrophy + motor cortex involvement | Midbrain atrophy (hummingbird) | Asymmetric frontoparietal atrophy |
Clinical Pearl
- Always examine FTD patients for fasciculations, wasting, and hyperreflexia at every visit — development of ALS features changes prognosis and goals of care dramatically
- CBS is a clinical syndrome, not a pathologic diagnosis — up to 50% of CBS cases have non-CBD pathology (most commonly AD)
Neuroimaging
Structural MRI Patterns
| FTD Variant | MRI Atrophy Pattern | Distinctive Feature |
|---|---|---|
| bvFTD | Bilateral frontal > anterior temporal; may be asymmetric | Frontal “knife-edge” atrophy; medial frontal and orbitofrontal involvement |
| nfvPPA | Left posterior inferior frontal (Broca area) and insula | Left perisylvian atrophy |
| svPPA | Left anterior temporal lobe (temporal pole) | Striking anterior temporal “knife-edge” atrophy, often strikingly asymmetric |
| lvPPA | Left posterior temporal and inferior parietal | Temporoparietal junction atrophy (overlaps with AD pattern) |
| C9orf72 carriers | Symmetric frontal, temporal, and parietal atrophy; may involve cerebellum and thalamus | More diffuse and symmetric than other genetic forms |
Functional Imaging
- FDG-PET: frontal and/or anterior temporal hypometabolism — pattern corresponds to clinical variant; more sensitive than MRI early in disease
- Amyloid PET: negative in true FTLD (distinguishes from AD); positive in lvPPA (confirms AD pathology)
- Tau PET: emerging tool; uptake pattern differs between AD tau and FTLD tau
💎 Board Pearl
- Amyloid PET is negative in FTD but positive in AD — the single best biomarker to distinguish FTD from AD when clinical overlap exists
- Frontal “knife-edge” atrophy on MRI is the classic imaging finding of FTD — gyri become razor-thin with prominent sulcal widening
- FDG-PET may show abnormalities before structural MRI — consider functional imaging when MRI appears normal in early disease
Differentiating FTD from Alzheimer Disease
| Feature | FTD (bvFTD) | Alzheimer Disease |
|---|---|---|
| Age of onset | 45–65 (younger) | >65 (older) |
| Presenting symptom | Personality/behavioral change | Memory loss |
| Memory | Relatively preserved early (retrieval deficit — improves with cueing) | Impaired early (encoding deficit — does NOT improve with cueing) |
| Visuospatial function | Preserved | Often impaired |
| Insight | Lost early (anosognosia) | Variable, may retain awareness early |
| Behavioral symptoms | Prominent disinhibition, apathy, compulsions, hyperorality | Behavioral changes later; apathy, depression |
| Language | May present as PPA variant | Word-finding difficulty; anomia |
| Atrophy pattern | Frontal > temporal; anterior predominant | Hippocampal and posterior temporal-parietal |
| Amyloid PET | Negative | Positive |
| CSF biomarkers | Normal Aβ42 and p-tau (or elevated NfL) | Low Aβ42, elevated p-tau and t-tau |
| ChEI response | No benefit; may worsen behavior | Modest benefit |
💎 Board Pearl
- Behavioral change + preserved memory + negative amyloid PET = bvFTD, not AD — the classic board differentiation
- Cholinesterase inhibitors may worsen bvFTD — can increase agitation, disinhibition, and behavioral symptoms; a commonly tested pitfall
- Neurofilament light chain (NfL) is elevated in FTD (especially FTD-ALS) and may help distinguish from psychiatric mimics, but is nonspecific
Treatment & Management
Pharmacologic Management
- No disease-modifying therapy currently approved for any FTD variant
- Treatment is symptomatic and focused on behavioral management and caregiver support
| Symptom | Treatment | Notes |
|---|---|---|
| Disinhibition, compulsions, agitation | SSRIs (sertraline, fluoxetine, citalopram); trazodone | SSRIs are first-line for behavioral symptoms; trazodone effective for agitation and sleep |
| Apathy | Structured routines; limited pharmacologic options | SSRIs may worsen apathy; stimulants sometimes tried but evidence limited |
| Psychosis/severe agitation | Low-dose atypical antipsychotics (quetiapine) as last resort | Use with extreme caution; increased mortality risk in dementia patients |
| Motor symptoms (PSP/CBD) | Levodopa trial | Usually poor response (<30% in PSP/CBD vs. robust in PD) |
| Language deficits (PPA) | Speech-language therapy | Focus on compensatory strategies and communication aids |
Medications to AVOID in bvFTD
- Cholinesterase inhibitors (donepezil, rivastigmine, galantamine) — no benefit in FTD; may worsen behavioral symptoms (disinhibition, agitation)
- Memantine — no demonstrated benefit in FTD; some studies suggest possible harm
- Typical antipsychotics — extrapyramidal side effects; contraindicated especially if parkinsonism present
Nonpharmacologic Interventions
- Structured daily routines and environmental modifications
- Caregiver education and support — FTD caregiver burden is extremely high due to young age of onset and behavioral symptoms
- Speech-language therapy for PPA variants (especially early in disease)
- Physical therapy and fall prevention (especially for PSP/CBD overlap)
- Advance care planning early in disease while capacity remains
- Genetic counseling for patients with family history or known mutations
Emerging Therapies
- Anti-sense oligonucleotides (ASOs) for C9orf72 — in clinical trials targeting repeat RNA
- Progranulin replacement for GRN carriers — gene therapy, antibody-based protein elevation, and small molecules under investigation
- Anti-tau therapies — immunotherapy and small molecule inhibitors in trials for FTLD-tau
Clinical Pearl
- The most important “treatment” in FTD is correct diagnosis — many patients spend years on cholinesterase inhibitors for presumed AD, which may worsen their behavioral symptoms
- Always discuss driving safety early: bvFTD patients often have impaired judgment and impulsivity that make driving dangerous, even before significant cognitive decline
Summary Board Pearls
💎 Board Pearl
- bvFTD = behavioral change + preserved memory + frontal atrophy — the most common FTD variant (~60%); onset typically 45–65
- nfvPPA = effortful, agrammatic speech + left posterior frontal atrophy — usually tau pathology (4R: CBD or PSP)
- svPPA = fluent empty speech + loss of word meaning + surface dyslexia + left anterior temporal atrophy — usually TDP-43 type C
- lvPPA = word-finding difficulty + impaired repetition + left temporoparietal atrophy = likely AD pathology — the only PPA variant that is usually amyloid-positive
- C9orf72 hexanucleotide repeat = #1 genetic cause of FTD and ALS — the single most important gene linking these two diseases
- FTLD pathology is classified by protein, not syndrome: FTLD-tau (Pick, PSP, CBD) vs. FTLD-TDP (types A–E) vs. FTLD-FUS
- Pick bodies = 3R tau; tufted astrocytes = PSP (4R tau); astrocytic plaques = CBD (4R tau)
- Avoid cholinesterase inhibitors in bvFTD — no benefit and may worsen behavioral symptoms; SSRIs and trazodone are first-line
- FTD vs. AD: behavioral change before memory loss, younger onset, frontal atrophy, negative amyloid PET
- FTD-ALS overlap (C9orf72) shortens survival to 2–3 years — screen all FTD patients for motor neuron signs
References
- Rascovsky K, Hodges JR, Knopman D, et al. Sensitivity of revised diagnostic criteria for the behavioural variant of frontotemporal dementia. Brain 2011;134(Pt 9):2456–2477.
- Gorno-Tempini ML, Hillis AE, Weintraub S, et al. Classification of primary progressive aphasia and its variants. Neurology 2011;76(11):1006–1014.
- Bang J, Spina S, Miller BL. Frontotemporal dementia. Lancet 2015;386(10004):1672–1682.
- Greaves CV, Rohrer JD. An update on genetic frontotemporal dementia. J Neurol 2019;266(8):2075–2086.
- DeJesus-Hernandez M, Mackenzie IR, Boeve BF, et al. Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 causes chromosome 9p-linked FTD and ALS. Neuron 2011;72(2):245–256.
- Mackenzie IR, Neumann M. Molecular neuropathology of frontotemporal dementia: insights into disease mechanisms from postmortem studies. J Neurochem 2016;138(Suppl 1):54–70.
- Tsai RM, Boxer AL. Diagnosis and management of frontotemporal dementia and its overlap with other neurodegenerative diseases. Curr Opin Neurol 2016;29(2):210–217.
- Rohrer JD, Warren JD. Phenotypic signatures of genetic frontotemporal dementia. Curr Opin Neurol 2011;24(6):542–549.
- Finger EC. Frontotemporal dementias. Continuum (Minneap Minn) 2016;22(2 Dementia):464–489.
- Boxer AL, Gold M, Feldman H, et al. New directions in clinical trials for frontotemporal lobar degeneration: methods and outcome measures. Alzheimers Dement 2020;16(1):131–143.
- Mesulam MM. Primary progressive aphasia. Ann Neurol 2001;49(4):425–432.
- Irwin DJ, Cairns NJ, Grossman M, et al. Frontotemporal lobar degeneration: defining phenotypic diversity through personalized medicine. Acta Neuropathol 2015;129(4):469–491.