Frontotemporal Dementia¶

Chapter 443 | Part 13: Neurologic Disorders

KEY CLINICAL POINTS¶

Frontotemporal dementia (FTD) encompasses clinical syndromes linked to frontotemporal lobar degeneration (FTLD) with abnormal protein aggregation (tau, TDP-43, or FET family proteins).
FTD most commonly presents in the fifth to seventh decades of life, with prevalence nearly equal to Alzheimer’s disease (AD) in this age group.
Genetic mutations in C9orf72, GRN, MAPT, and other genes account for 10–20% of familial cases, with autosomal dominant inheritance.
Neuroimaging (MRI) reveals focal atrophy in frontal, temporal, or parietal regions, while tau PET ligands show promise for in vivo detection of pathologic tau.
Symptomatic management is the mainstay, with no disease-modifying therapies available; antidepressants may alleviate behavioral symptoms.

1. DEFINITION & OVERVIEW¶

Frontotemporal dementia (FTD) refers to a group of clinical syndromes united by their association with frontotemporal lobar degeneration (FTLD) pathology. FTD is characterized by progressive degeneration of frontal and temporal lobes, leading to behavioral, language, or motor dysfunction. It is distinct from Alzheimer’s disease (AD) and other dementias due to its unique proteinopathies (tau, TDP-43, or FET family proteins).

FTLD Subtypes by Protein Pathology¶

Protein Type	Clinical Syndromes	Key Features
Tau	Pick’s disease, corticobasal degeneration (CBD), progressive supranuclear palsy (PSP)	Hyperphosphorylated 4-repeat tau inclusions
TDP-43	Frontotemporal dementia with motor neuron disease (FTD-MND), amyotrophic lateral sclerosis (ALS)	Neuronal and glial TDP-43 inclusions
FET Family (FUS, Ewing, TAF-15)	Frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17)	FUS or Ewing protein inclusions

1.1 Core Clinical Syndromes¶

Three primary syndromes: (1) Behavioral variant FTD (bvFTD) with apathy, disinhibition, and executive dysfunction; (2) Semantic variant primary progressive aphasia (svPPA) with loss of word/meaning comprehension; (3) Nonfluent/agrammatic variant PPA (nfvPPA) with speech production impairment. FTD-MND (FTD with motor neuron disease), corticobasal syndrome (CBS), and progressive supranuclear palsy–Richardson syndrome (PSP-RS) are also included.

1.2 Pathophysiology¶

FTLD is driven by abnormal protein aggregation (tau, TDP-43, or FET proteins). TDP-43 pathology is most common, while tauopathies (e.g., Pick’s disease) and FET-related disorders (e.g., amyotrophic lateral sclerosis) are less frequent. Misfolded proteins exhibit prion-like propagation, leading to network-specific degeneration.

2. EPIDEMIOLOGY¶

FTD is nearly as prevalent as Alzheimer’s disease in the fifth to seventh decades of life. Male predominance was historically noted but recent studies suggest no significant gender difference. Family history is common, with autosomal dominant inheritance in 10–20% of cases. Risk factors include age, genetic mutations, and comorbid conditions (e.g., Parkinson’s disease).

2.1 Demographics¶

Median age of onset: 55–65 years. No significant gender difference in recent studies. Familial clustering in 10–20% of cases.

2.2 Prevalence¶

Estimated prevalence: 1–2 per 10,000 adults. Nearly as common as AD in the fifth to seventh decades. Up to 30% of patients with corticobasal syndrome (CBS) may have AD pathology at autopsy.

3. ETIOLOGY & PATHOPHYSIOLOGY¶

FTD is caused by genetic mutations (C9orf72, GRN, MAPT) leading to protein misfolding and aggregation. TDP-43 and FET proteins are central to pathogenesis, with prion-like propagation of misfolded proteins contributing to disease spread. Tauopathies (e.g., Pick’s disease) involve hyperphosphorylated tau inclusions.

3.1 Genetic Mutations¶

C9orf72 hexanucleotide (GGGGCC) repeat expansion: Most common cause of familial and sporadic FTD. GRN mutations (progranulin deficiency) and MAPT mutations (tau misfolding) are also implicated.

3.2 Protein Pathology¶

TDP-43: Neuronal and glial inclusions with dipeptide repeat proteins. FET family: FUS, Ewing, TAF-15 inclusions. Tau: Hyperphosphorylated 4-repeat tau in Pick’s disease and CBD.

3.3 Molecular Mechanisms¶

Misfolded proteins act as templates for pathological spreading via prion-like mechanisms. TDP-43 dysfunction disrupts mRNA processing, leading to neuroinflammation and neuronal loss.

4. CLINICAL FEATURES¶

FTD presents with behavioral, language, or motor symptoms. bvFTD shows apathy, disinhibition, and executive dysfunction. svPPA involves semantic memory loss. nfvPPA features speech production deficits. FTD-MND combines dementia with motor neuron disease. PSP-RS and CBS show progressive motor and cognitive decline.

4.1 Behavioral Variant FTD (bvFTD)¶

Apathy, disinhibition, compulsivity, loss of empathy, overeating, and executive dysfunction. May progress to PSP-RS or CBS.

4.2 Primary Progressive Aphasia (PPA)¶

Semantic variant: Loss of word/meaning comprehension. Nonfluent/agrammatic variant: Speech production impairment with motor speech deficits.

4.3 Motor and Cognitive Features¶

FTD-MND: Dementia with motor neuron disease. PSP-RS: Progressive supranuclear ophthalmoplegia, axial rigidity, and falls. CBS: Asymmetric rigidity, dystonia, and apraxia.

5. DIFFERENTIAL DIAGNOSIS¶

FTD must be differentiated from schizophrenia, pseudodementia, vascular dementia, AD, and other neurodegenerative disorders. Psychogenic amnesia, conversion disorder, and drug-induced dementia are also considered.

5.1 Psychiatric Mimics¶

Schizophrenia: Complex delusions/hallucinations vs. FTD’s simpler symptoms. Pseudodementia: Depressed patients with intact memory vs. true dementia.

5.2 Other Dementias¶

AD: Spared frontal lobes vs. FTD’s frontal/temporal atrophy. Vascular dementia: Stepwise decline vs. FTD’s gradual progression. DLB: Fluctuating cognition vs. FTD’s stable patterns.

6. INVESTIGATIONS & DIAGNOSIS¶

Diagnosis combines clinical evaluation, neuroimaging, cognitive testing, and biomarkers. MRI shows frontal/temporal atrophy. Tau PET ligands detect pathologic tau, though limited to AD-related patterns. Genetic testing identifies C9orf72, GRN, or MAPT mutations.

6.1 Neuroimaging¶

MRI: Frontal/insular/temporal atrophy. PET: Tau ligands (e.g., [18F]Flortaucipir) for in vivo detection of tau pathology.

6.2 Biomarkers¶

CSF: No specific markers for FTD. Tau PET: Promising but limited to AD-related tau. CSF amyloid-beta is negative in FTD.

6.3 Genetic Testing¶

C9orf72, GRN, and MAPT mutations are tested in familial cases. GRN mutations may also cause neuronal ceroid lipofuscinosis.

7. MANAGEMENT & TREATMENT¶

Symptomatic management is the mainstay. Antidepressants (SSRIs) for behavioral symptoms. Antipsychotics used cautiously due to risk of worsening parkinsonism. No disease-modifying therapies are available, though experimental agents (e.g., donanemab) are in trials.

7.1 Symptomatic Treatment¶

SSRIs for depression, irritability, and compulsions. Antipsychotics (e.g., risperidone) for severe behavioral symptoms, with caution for parkinsonism.

7.2 Experimental Therapies¶

Anti-TDP-43 antibodies, tau-targeting agents, and gene therapies are under investigation. Donanemab and lecanemab show limited efficacy in early trials.

8. PROGNOSIS & COMPLICATIONS¶

FTD has a median survival of 5–10 years. Complications include motor neuron disease, parkinsonism, and progression to PSP-RS or CBS. Psychiatric comorbidities (e.g., depression) and caregiver burden are significant challenges.

8.1 Survival¶

Median survival: 5–10 years. FTD-MND and PSP-RS have shorter survival due to motor complications.

8.2 Complications¶

Progression to motor neuron disease, parkinsonism, or other syndromes. Psychiatric symptoms (e.g., depression) and caregiver stress are major challenges.

9. SPECIAL CONSIDERATIONS¶

Caregiver support is critical due to behavioral and emotional dysfunction. Distinguish FTD from psychiatric conditions (e.g., schizophrenia) and drug-induced dementia. Genetic counseling is important for families with hereditary mutations.

9.1 Psychiatric Comorbidities¶

Depression, irritability, and compulsions are common. Antidepressants may alleviate symptoms, but antipsychotics require caution.

9.2 Genetic Counseling¶

C9orf72, GRN, and MAPT mutations have autosomal dominant inheritance. Family screening is recommended for at-risk individuals.

10. KEY POINTS & CLINICAL PEARLS¶

FTD is a heterogeneous group of syndromes linked to FTLD with tau, TDP-43, or FET proteinopathies. 2. Neuroimaging (MRI) and tau PET are critical for diagnosis. 3. Genetic testing identifies C9orf72, GRN, or MAPT mutations. 4. Symptomatic management is the mainstay, with no disease-modifying therapies. 5. Distinguish FTD from psychiatric conditions and other dementias using clinical and biomarker data.