Clinical Reference · Cognitive Neurology

Differentiating the Dementias

Six patterns, one bedside key — the feature that names each dementia
Alzheimer
Alzheimer disease (AD)
Onset 65+ · most common
Insidious episodic memory loss — encoding failure that doesn't improve with cueing
Cognitive · Early
Forgets recent events, repeats questions; visuospatial & word-finding later
Exam · Motor
Normal until late in the course
Imaging · Biomarker
Hippocampal / temporoparietal atrophy · CSF ↓Aβ42 ↑p-tau · amyloid PET+
Lewy body
Dementia with Lewy bodies (DLB)
Onset 50+
Fluctuating cognition + recurrent well-formed visual hallucinations
Core Features
Parkinsonism, REM sleep behavior disorder, fluctuations; severe neuroleptic sensitivity
Exam · Motor
Spontaneous parkinsonism (dementia within ~1 yr of motor signs)
Imaging · Biomarker
DaTscan ↓ striatal uptake · occipital hypometabolism · abnormal MIBG
Frontotemporal
Behavioral variant FTD (bvFTD)
Onset 45–65 · younger
Early personality & behavior change — memory relatively spared at first
Cognitive · Early
Disinhibition, apathy, loss of empathy, compulsions, hyperorality
Exam · Motor
Late; may overlap PSP / CBS / motor neuron disease
Imaging · Biomarker
Frontal + anterior temporal atrophy · tau or TDP-43 pathology
Vascular
Vascular dementia (VaD)
Onset 60+
Stepwise decline with prominent executive dysfunction
Cognitive · Early
Slowed processing, poor attention/executive; recognition > recall
Exam · Motor
Focal signs, early gait disorder; vascular risk factors
Imaging · Biomarker
Cortical / lacunar infarcts · extensive white-matter disease
PSP
Progressive supranuclear palsy
Onset 60+ · atypical parkinsonism
Vertical gaze palsy + early backward falls
Cognitive · Early
Frontal-executive slowing, apathy, pseudobulbar affect
Exam · Motor
Vertical supranuclear gaze palsy (down > up), axial rigidity
Imaging · Biomarker
Midbrain atrophy — "hummingbird" sign · 4R tauopathy
NPH
Normal-pressure hydrocephalus
Onset 60+
Treatable
Gait + urinary + cognitive triad — "wet, wobbly, wacky" · potentially reversible
Cognitive · Early
Subcortical slowing; gait comes first & is most reversible; urinary urgency
Exam · Motor
Broad-based magnetic / apraxic gait
Imaging · Biomarker
Ventriculomegaly out of proportion (Evans >0.3), DESH · improves after high-volume LP → shunt
⚡Don't miss the fast one
Rapidly progressive (weeks–months) + myoclonus + ataxia → think CJD — DWI cortical ribboning / basal-ganglia signal, RT-QuIC & 14-3-3.
🔎Always exclude reversible mimics
B12, TSH, HIV/RPR, medications, depression (pseudodementia), and NPH — the structural, shunt-responsive cause above.
Sources: Neuro.Wiki › Cognitive Neurology / Dementia. McKeith DLB criteria (Neurology 2017) · Rascovsky bvFTD criteria (2011) · MDS-PSP criteria (2017) · DSM-5. Educational reference — not a substitute for clinical judgment. Neuro.Wiki