Neurodegenerative Disorders: Approach, Diagnosis, Investigations, Treatment & Pathognomonic Signs
Complete evidence-based monographs for AD, DLB, FTD, IPD, PSP, MSA, CBS/CBD, ALS/MND, Huntington's Disease, sCJD, and iNPH — including 2022–2024 diagnostic criteria, MRI/PET hallmarks, CSF/Plasma biomarkers (p-tau217, RT-QuIC, NfL), and disease-modifying therapies (Lecanemab, Donanemab, Tofersen).
Alzheimer's Disease (AD)
Extracellular β-Amyloid (Aβ42) plaques + Intracellular Hyperphosphorylated Tau (3R+4R) Neurofibrillary Tangles
Dementia with Lewy Bodies (DLB)
Alpha-Synuclein (Lewy bodies & Lewy neurites in neocortex, limbic cortex, and brainstem) + frequent co-existent AD amyloid pathology
Frontotemporal Degeneration (bvFTD, svPPA, nfvPPA)
FTLD-TDP (TDP-43, ~50%), FTLD-Tau (3R Pick bodies or 4R Tau, ~45%), or FTLD-FUS (~5%)
Idiopathic Parkinson's Disease (IPD)
Alpha-Synuclein (Lewy bodies in Substantia Nigra pars compacta [SNpc], ascending via Braak Stages 1–6 from dorsal motor nucleus of vagus & olfactory bulb)
Progressive Supranuclear Palsy (PSP)
4-Repeat (4R) Tauopathy ("Tufted Astrocytes" & globose neurofibrillary tangles in midbrain, STN, globus pallidus, and dentate nucleus)
Multiple System Atrophy (MSA-P & MSA-C)
Alpha-Synucleinopathy inside Oligodendrocytes — Papp-Lantos Glial Cytoplasmic Inclusions (GCIs) causing striatonigral degeneration & olivopontocerebellar atrophy
Corticobasal Degeneration / Syndrome (CBD / CBS)
4-Repeat (4R) Tauopathy ("Astrocytic Plaques", ballooned achromatic neurons, and corticobasal bodies); Note: Clinical CBS can also be caused by AD, PSP, or TDP-43 pathology
Amyotrophic Lateral Sclerosis (ALS / Motor Neuron Disease)
TDP-43 Cytoplasmic Inclusions + Bunina Bodies (~97% of all ALS); SOD1 (~2%, lacks TDP-43!) or FUS (~1%)
Huntington's Disease (HD)
Mutant Huntingtin Protein (mHTT) with expanded polyglutamine (PolyQ) tract causing selective loss of GABAergic Medium Spiny Neurons in the Caudate & Putamen (Striatum)
Sporadic Creutzfeldt-Jakob Disease (sCJD / Prion Disease)
Misfolded Protease-Resistant Prion Protein (PrP^Sc converting normal α-helical cellular PrP^C into β-sheet rich PrP^Sc) causing spongiform encephalopathy
Idiopathic Normal Pressure Hydrocephalus (iNPH — Reversible Mimic)
Impaired CSF dynamics & glymphatic clearance (Non-obstructive communicating hydrocephalus; ~30–40% have co-existent AD or vascular pathology on cortical biopsy)
Alzheimer's Disease (AD)
Insidious anterograde episodic memory loss (hippocampal type: poor free recall NOT rescued by cueing) + visuospatial/language/executive decline.
Extracellular β-Amyloid (Aβ42) plaques + Intracellular Hyperphosphorylated Tau (3R+4R) Neurofibrillary Tangles
Pathognomonic & Hallmark Signs (AD)
- •Head-Turning Sign: Patient immediately turns to look at caregiver when asked a direct history question
- •Hippocampal Amnestic Pattern: Failure to benefit from semantic cues on delayed recall testing (unlike FTD/subcortical dementia)
- •MTA (Medial Temporal Lobe Atrophy) Score ≥2–3 on Coronal T1 MRI: Disproportionate hippocampal, parahippocampal, and entorhinal cortex atrophy with widened choroid fissure
- •Posterior Cingulate & Precuneus Atrophy / Hypometabolism (especially prominent in early-onset AD)
- •Koedam Posterior Parietal Atrophy in PCA variant
- •AT(N) Biomarker Profile: Decreased CSF Aβ42 (or Aβ42/Aβ40 ratio <0.06) + Increased CSF p-tau181 / Plasma p-tau217 + Increased t-tau/NfL
- •Amyloid PET (Florbetapir, Flutemetamol, Pittsburgh Compound B) diffuse cortical uptake & Tau PET (Flortaucipir) Braak stage propagation
- •FDG-PET: Temporoparietal + Posterior Cingulate / Precuneus hypometabolism (sparing primary sensorimotor and occipital cortex)
Clinical Presentation & Disease Evolution
- • Impaired episodic memory for recent events (repeating questions, misplacing items)
- • Anomia / word-finding pauses and loss of semantic fluency (animals > letter fluency)
- • Topographical disorientation (getting lost in familiar routes)
- • Amnestic Syndrome of Hippocampal Type: impaired encoding/consolidation — cueing does NOT normalize recall
- • Atypical Non-Amnestic Variants: Posterior Cortical Atrophy (PCA - Balint/Gerstmann), Logopenic PPA (lvPPA - impaired sentence repetition), Frontal/Dysexecutive AD
- • Ideomotor apraxia and visuospatial constructional deficits (clock drawing)
- • Behavioral & psychological symptoms of dementia (BPSD): apathy, agitation, delusions of theft
- • Myoclonus and late-onset focal or generalized seizures
- • Loss of ambulation, dysphagia, and mutism in end-stage
- • Early prominent parkinsonism or recurrent visual hallucinations within 1 year (think DLB)
- • Early behavioral disinhibition, hyperorality, or apathy with spared memory (think bvFTD)
- • Stepwise deterioration with focal pyramidal signs or acute onset (think Vascular Dementia)
- • Rapid progression over weeks to months with myoclonus (think CJD or Autoimmune Encephalitis)
Diagnostic Criteria
NIA-AA (2018/2024 Revised Criteria) & IWG-2 Criteria
- • Insidious onset and gradual progression of cognitive impairment over ≥6 months
- • Core 1 Biomarkers (sufficient for biological AD diagnosis): Amyloid PET positive, CSF Aβ42/40 + p-tau181 ratio, or high-accuracy Plasma p-tau217
- • Core 2 Biomarkers (staging & prognosis): Tau PET (neocortical tangle burden)
- • Amnestic presentation or classic non-amnestic syndromic variant (PCA, lvPPA)
- • APOE ε4 homozygosity or autosomal dominant mutation (PSEN1, PSEN2, APP)
- • Hippocampal volume loss on volumetric MRI
- • Substantial concomitant cerebrovascular disease temporally related to cognitive onset
- • Core features of DLB, bvFTD, or reversible metabolic/infectious encephalopathies
Diagnostic Investigations Workup
Evidence-Based Treatment & Pharmacotherapy
- • Lecanemab (IV q2w): Anti-Aβ protofibril mAb for MCI / Mild AD with confirmed amyloid; slows decline by 27% at 18m (CLARITY-AD). Requires serial MRI monitoring for ARIA-E (edema) and ARIA-H (hemorrhage).
- • Donanemab (IV q4w): Anti-pyroglutamate Aβ plaque mAb for early symptomatic AD; slows decline by 35% in low/medium tau population (TRAILBLAZER-ALZ 2); can stop dosing once amyloid plaque clearance achieved.
- • Acetylcholinesterase Inhibitors (AChEIs) for Mild-to-Severe AD: Donepezil (5–10 mg OD; 23 mg in moderate-severe), Rivastigmine (oral or 4.6–13.3 mg/24h transdermal patch), Galantamine (8–24 mg/d).
- • NMDA Receptor Antagonist for Moderate-to-Severe AD: Memantine (titrate 5 mg/d weekly to 10 mg BID; reduces glutamate excitotoxicity).
- • Brexpiprazole (FDA-approved for agitation in AD) or SSRIs (Citalopram/Sertraline) for neuropsychiatric symptoms.
- • Aerobic exercise, Mediterranean/MIND diet, hearing aid correction (Lancet Commission modifiable risk factor)
- • Cognitive stimulation therapy and structured caregiver support
- • Anticholinergics (Oxybutynin, Diphenhydramine, TCAs: Amitriptyline) — directly worsen cholinergic deficit and precipitate delirium
- • Benzodiazepines and Z-drugs (paradoxical agitation, falls)
- • Systemic thrombolytics (tPA/TNK) and therapeutic anticoagulation require extreme caution in patients on Lecanemab/Donanemab due to fatal intracerebral hemorrhage risk with ARIA