This page provides a comprehensive comparison of Alzheimer's Disease (AD), Parkinson's Disease (PD), and Frontotemporal Dementia (FTD)—three major neurodegenerative disorders with overlapping but distinct clinical and pathological features. Understanding their similarities and differences is essential for accurate diagnosis, prognostic counseling, and therapeutic development[1].
| Feature | Alzheimer's Disease | Parkinson's Disease | Frontotemporal Dementia |
|---|---|---|---|
| Onset Age | Typically >65 years | Typically >60 years | Typically 45-65 years |
| Prevalence | ~6 million (US) | ~1 million (US) | ~50,000-60,000 (US) |
| Key Pathology | Amyloid plaques, neurofibrillary tangles | Lewy bodies (α-synuclein) | Tau or TDP-43 inclusions[2] |
| Primary Proteins | Aβ, tau | α-synuclein[3] | Tau, TDP-43 |
| Affected Regions | Hippocampus, cortex | Substantia nigra, basal ganglia | Frontal and temporal lobes[4] |
| Motor Symptoms | Late stage | Early, prominent | Variable |
| Cognitive Symptoms | Memory loss prominent | Executive dysfunction | Language, behavior prominent |
| Memory Loss | Early, prominent | Variable | Usually later |
| Disease Duration | 8-12 years | 15-20 years | 6-11 years |
Alzheimer's Disease:
Parkinson's Disease:
Frontotemporal Dementia:
| Risk Factor | AD | PD | FTD |
|---|---|---|---|
| Age | Primary risk factor | Primary risk factor | Earlier onset |
| Family history | Significant | Significant | Strong (40-50% cases) |
| APOE ε4 | Strong risk | No effect | No effect |
| Head trauma | Possible risk | Possible risk | Possible |
| Education | Lower = higher risk | No clear effect | No clear effect |
AD is characterized by two hallmark proteinopathies[5]:
Amyloid plaques: Extracellular deposits of Aβ peptides (primarily Aβ42)
Neurofibrillary tangles: Intracellular aggregates of hyperphosphorylated tau
Lewy bodies: Intraneuronal inclusions containing α-synuclein
Degeneration of dopaminergic neurons
FTD encompasses multiple proteinopathies[2:1]:
FTLD-tau (~40% of cases):
FTLD-TDP (~50% of cases):
FTLD-FUS (~10% of cases):
| Symptom | AD | PD | FTD |
|---|---|---|---|
| Tremor | Rare | Early, resting | Rare |
| Bradykinesia | Late | Early, prominent | Rare |
| Rigidity | Late | Early, prominent | Variable |
| Gait disturbance | Late | Early | Variable |
| Falls | Late | Early | Variable |
| Postural instability | Late | Early (H&Y 3+) | Variable |
| Dystonia | Rare | Variable | Variable |
| Myoclonus | Rare (late) | Variable | Variable |
| Domain | AD | PD | FTD |
|---|---|---|---|
| Memory | Early, prominent | Working memory | Episodic relatively spared |
| Executive function | Early | Early | Early, prominent |
| Language | Late | Variable | Early, prominent |
| Visuospatial | Early | Variable | Usually spared |
| Behavior | Late | Variable | Early, prominent |
| Social cognition | Late | Variable | Early (bvFTD) |
| Gene | Variant | Effect | Notes |
|---|---|---|---|
| APOE | ε4 | Strong risk | Most significant genetic factor |
| APOE | ε2 | Protective | Reduces risk by ~40% |
| TREM2 | R47H | Moderate risk | Immune receptor, microglial function |
| APP | Swedish | Causative | Early-onset familial AD |
| PSEN1 | Multiple | Causative | Early-onset familial AD |
| PSEN2 | Multiple | Causative | Early-onset familial AD |
| Gene | Effect | Inheritance | Notes |
|---|---|---|---|
| LRRK2 | Moderate risk | Autosomal dominant | Most common genetic cause |
| GBA | Moderate risk | Autosomal recessive | Faster cognitive decline |
| SNCA | Causative | Autosomal dominant | First identified PD gene |
| PARKIN | Early-onset | Autosomal recessive | Juvenile onset |
| PINK1 | Early-onset | Autosomal recessive | Similar to PARKIN |
| DJ-1 | Early-onset | Autosomal recessive | Rare |
| Gene | Effect | Protein | Notes |
|---|---|---|---|
| MAPT | Causative/risk | Tau | Intron mutations, P301L |
| GRN | Causative | Progranulin | Haploinsufficiency |
| C9orf72 | Causative | Dipeptide repeats | Most common cause |
| VCP | Causative | Valosin-containing protein | PDBSS syndrome |
| FUS | Rare | FUS protein | ALS-FTD overlap |
| Biomarker | AD | PD | FTD |
|---|---|---|---|
| Amyloid PET | Positive | Negative | Usually negative |
| Tau PET | Positive (AD pattern) | Variable (Limbic) | Variable (FTD pattern) |
| CSF Aβ42 | Decreased | Normal | Normal |
| CSF total tau | Increased | Normal | Normal (usually) |
| CSF p-tau | Increased | Normal | Normal (usually) |
| α-synuclein RT-QuIC | Negative | Positive (70-90%) | Negative |
| Neurofilament light | Increased (later) | Increased (later) | Increased |
| FDG-PET | Temporoparietal hypometabolism | Posterior cingulate | Frontal hypometabolism |
Imaging Biomarkers:
Fluid Biomarkers[7]:
| Approach | AD | PD | FTD |
|---|---|---|---|
| Cholinesterase inhibitors | Donepezil, rivastigmine, galantamine | May help (especially with dementia) | Limited benefit |
| NMDA antagonist | Memantine | Not standard | Not standard |
| Dopamine agonists | Not used | Pramipexole, ropinirole | Not used |
| Levodopa | Not used | First-line | Not used |
| Immunotherapy | Lecanemab, donanemab | In development | In development |
| Anti-aggregants | In trials | In trials | In trials |
| Gene therapy | Emerging | Emerging | Emerging |
Alzheimer's Disease:
Parkinson's Disease:
Frontotemporal Dementia:
| Stage | Duration | Features |
|---|---|---|
| Preclinical | Years to decades | Biomarkers positive, no symptoms |
| MCI due to AD | 2-5 years | Objective deficits, preserved function |
| Mild dementia | 2-4 years | Memory loss, instrumental ADLs affected |
| Moderate dementia | 2-6 years | Basic ADLs require assistance |
| Severe dementia | 1-3 years | Complete dependency |
| Stage | Duration | Features |
|---|---|---|
| Prodromal | Years to decades | RBD, hyposmia, depression |
| Early (H&Y 1-2) | 3-5 years | Motor symptoms, good levodopa response |
| Mid (H&Y 2.5-3) | 5-10 years | Motor fluctuations, dyskinesias |
| Advanced (H&Y 4) | 10-15 years | Disability, falls |
| End-stage (H&Y 5) | 15-20 years | Wheelchair, severe disability |
| Stage | Duration | Features |
|---|---|---|
| Early | 0-3 years | Focal symptoms, preserved function |
| Middle | 3-6 years | Behavioral/cognitive changes |
| Late | 6-10 years | Severe impairment, nursing home |
| End-stage | 8-15 years | Complete dependency |
Izzy S, Grinberg LT, Solomon J, et al. Neuropathological comparison of three major dementias. Acta Neuropathol. 2019. ↩︎
Neumann M, Mackenzie IR. TDP-43 pathology in FTD and ALS. Nat Rev Neurol. 2019. ↩︎ ↩︎
Spillantini MG, Goedert M. Alpha-synuclein and Parkinson's disease. Philos Trans R Soc Lond B Biol Sci. 2000. ↩︎ ↩︎
Seeley WW, Crawford R, Rascovsky K, et al. Frontal networks in frontotemporal dementia and Alzheimer disease. Am J Geriatr Psychiatry. 2009. ↩︎
Beach TG, Adler CH, Lue L, et al. Staging of Alzheimer's disease-related neuropathological changes. J Neuropathol Exp Neurol. 2018. ↩︎
Kalia LV, Lang AE. Parkinson's disease. Lancet. 2015. ↩︎
Blennow K, Zetterberg H. Biomarkers for Alzheimer's disease. J Intern Med. 2019. ↩︎