Clinical Reference · Cognitive Neurology

Subtypes of Alzheimer Disease

Beyond amnestic — the atypical presentations that still carry AD pathology
Amnestic
Typical (amnestic) AD
Onset 65+ · ~80% of cases
Progressive episodic memory loss — medial temporal onset
Hallmark
Recent-memory encoding failure; later language, visuospatial & executive decline
Distinguishing
Amnestic-predominant; APOE ε4 = main risk gene
Atrophy · Biomarker
Hippocampal → temporoparietal · amyloid+ tau+
PCA
Posterior cortical atrophy (Benson)
Onset 50–65 · visual variant
Progressive visuospatial / visuoperceptual decline — memory spared early
Key Signs
Bálint (simultanagnosia, optic ataxia, ocular apraxia), Gerstmann, dressing apraxia
Distinguishing
Cortical visual failure with a normal eye exam
Atrophy · Biomarker
Occipito-parietal atrophy · AD pathology (amyloid+)
lvPPA
Logopenic variant PPA
Onset 50–70 · language variant
Word-finding pauses + impaired sentence repetition
Key Signs
Phonological (sound) errors, anomia; grammar & single-word comprehension spared
Distinguishing
Most lvPPA = AD pathology (other PPA variants = FTD)
Atrophy · Biomarker
Left temporoparietal atrophy · amyloid+
Frontal
Behavioral / dysexecutive AD
Onset often <65
Executive / behavioral decline mimicking bvFTD
Key Signs
Dysexecutive, poor attention; some apathy / disinhibition
Distinguishing
AD pathology despite an FTD-like picture — amyloid+ separates it
Atrophy · Biomarker
Frontal + parietal · amyloid+ tau+
EOAD
Early-onset AD (<65)
Onset 40s–50s
AD before 65 — more often non-amnestic & aggressive
Key Signs
Higher rate of PCA / lvPPA / frontal variants; faster decline
Distinguishing
Mostly sporadic; less APOE-driven than late-onset
Atrophy · Biomarker
Prominent neocortical / parietal atrophy · amyloid+
ADAD
Autosomal-dominant / familial AD
Onset 30s–50s
Genetic
Fully penetrant familial AD — APP · PSEN1 · PSEN2
Key Signs
PSEN1 earliest & most common; myoclonus, seizures, spastic paraparesis variants
Distinguishing
Down syndrome (APP triplication) → near-universal AD by 60s
Atrophy · Biomarker
Amyloid rises decades pre-symptom (DIAN) · basis of prevention trials
⚡Don't miss the masquerader
Young-onset or non-amnestic dementia with amyloid+ biomarkers is an AD variant — not FTD. Check before you label it.
🔎Confirm the pathology
Atypical AD needs amyloid PET or CSF Aβ42:40 + p-tau — especially before any anti-amyloid therapy.
Sources: Neuro.Wiki › Cognitive Neurology / Alzheimer Disease. IWG / Dubois criteria · Crutch PCA consensus (2017) · Gorno-Tempini PPA criteria (2011) · NIA-AA. Educational reference — not a substitute for clinical judgment. Neuro.Wiki