Neurodegenerative Inclusions & Proteinopathies

For a century neurodegenerative diseases were defined by their clinical syndromes — a tremor here, an aphasia there, a relentless dementia. Modern neuropathology tells a deeper story: most of these disorders are proteinopathies, defined by a specific misfolded protein that aggregates, resists clearance, and seeds its neighbors. Learn the disease by its culprit protein and the morphology of its inclusion, and the histology slide tells you the diagnosis before the clinical chart does. What follows is an accuracy-first tour organized by the offending protein — amyloid-β, tau, alpha-synuclein, TDP-43, polyglutamine, and the prion protein — plus a handful of aging-related "bystander" inclusions worth recognizing.

Amyloid-β

• Neuritic (senile) plaques — extracellular deposits of amyloid-β with a dense amyloid core surrounded by dystrophic neurites, the histologic signature of Alzheimer disease. Amyloid-β is generated by sequential cleavage of amyloid precursor protein (APP) by β- and γ-secretase.
• Cerebral amyloid angiopathy (CAA) — amyloid-β deposited in the walls of small-to-medium leptomeningeal and cortical arteries, weakening the vessel and predisposing to lobar intracerebral hemorrhage in the elderly. CAA frequently coexists with Alzheimer pathology but is a distinct vascular process.

Pearl: The two amyloid-β diseases differ by where the protein lands — parenchymal plaques drive Alzheimer dementia, vascular amyloid drives lobar hemorrhage.

Tau (the tauopathies)

Tau is a microtubule-associated protein; when hyperphosphorylated it detaches, misfolds, and aggregates into filaments. The morphology of those aggregates separates the tauopathies.

• Neurofibrillary tangles (NFTs) — intraneuronal bundles of paired helical filaments of hyperphosphorylated tau, classically seen in Alzheimer disease (alongside the amyloid-β plaques above). NFT burden and distribution track with cognitive decline.
• Pick bodies — round, well-circumscribed, tau-positive intracytoplasmic neuronal inclusions found in Pick disease, a form of frontotemporal lobar degeneration (FTLD-tau), often with accompanying ballooned "Pick cells."
• Globose neurofibrillary tangles and tufted astrocytes — characteristic of progressive supranuclear palsy (PSP), a 4-repeat tauopathy affecting brainstem and basal ganglia.
• Astrocytic plaques and ballooned (achromatic) neurons — the hallmark glial and neuronal tau lesions of corticobasal degeneration (CBD), also a 4-repeat tauopathy.

Pearl: Tufted astrocytes point to PSP; astrocytic plaques point to CBD — the astrocytic lesion is the most reliable way to separate these two 4R tauopathies on a slide.

Alpha-synuclein (the synucleinopathies)

• Lewy bodies — round, eosinophilic intracytoplasmic inclusions with a dense core and a pale peripheral halo, classically within the pigmented neurons of the substantia nigra in Parkinson disease. Their principal component is aggregated alpha-synuclein.
• Cortical Lewy bodies — alpha-synuclein inclusions distributed through the cerebral cortex (limbic and neocortical) in dementia with Lewy bodies; they tend to lack the discrete halo of the brainstem-type body.
• Glial cytoplasmic inclusions (Papp–Lantos bodies) — alpha-synuclein aggregates within oligodendrocytes, the defining lesion of multiple system atrophy.

Pearl: All three are alpha-synuclein, but the cell of residence differs — neuronal in Parkinson disease and DLB, oligodendroglial in MSA. The glial cytoplasmic inclusion is what makes MSA an "oligodendrogliopathy."

TDP-43 (the TDP-43 proteinopathies)

• Cytoplasmic TDP-43 inclusions — abnormal ubiquitinated, phosphorylated TDP-43 mislocalized from nucleus to cytoplasm, found in motor neurons of amyotrophic lateral sclerosis (ALS) and in the most common molecular subtype of frontotemporal lobar degeneration, FTLD-TDP.
• Bunina bodies — small, eosinophilic intracytoplasmic inclusions within surviving anterior horn (lower motor) neurons, a relatively specific finding in ALS. Note that Bunina bodies are a distinct morphologic inclusion and are not composed of TDP-43; they are not the TDP-43 proteinopathy itself but a separate, ALS-associated finding that frequently coexists with the cytoplasmic TDP-43 inclusions above.

Pearl: ALS and frontotemporal dementia sit on one molecular spectrum — both are usually TDP-43 proteinopathies, which is why a single patient (and a single C9orf72 expansion) can show both phenotypes.

Polyglutamine / huntingtin

• Intranuclear neuronal inclusions — aggregates of mutant huntingtin protein bearing an expanded polyglutamine tract, the consequence of a CAG trinucleotide repeat expansion in the HTT gene, seen in Huntington disease. Grossly, the disease is recognized by atrophy of the caudate and putamen.

Prion protein (PrP-Sc)

• Spongiform change — fine vacuolation of the neuropil without inflammation, the histologic hallmark of Creutzfeldt–Jakob disease and the other transmissible spongiform encephalopathies. The absence of an inflammatory infiltrate is a key discriminator from infectious encephalitis.
• Florid (kuru-type) plaques — amyloid PrP plaques surrounded by a halo of spongiform vacuoles, characteristically abundant in variant CJD.

Aging- and Alzheimer-associated "bystander" inclusions

Two further inclusions are worth recognizing because they cluster in the aging and Alzheimer hippocampus but are not disease-defining on their own:

• Hirano bodies — eosinophilic, rod-shaped intracytoplasmic inclusions rich in actin, seen in and around hippocampal pyramidal neurons; common in aging and increased in Alzheimer disease.
• Granulovacuolar degeneration — intracytoplasmic vacuoles each containing a small dense granule, concentrated in hippocampal pyramidal neurons in aging and Alzheimer disease.

Quick-reference table

A word of caution

Inclusions are diagnostic clues, not absolute proofs. Mixed pathology is the rule, not the exception, in the aging brain — concurrent Alzheimer (amyloid-β plus tau), Lewy body, TDP-43, and vascular changes routinely coexist in a single specimen. Definitive subtyping (for example, separating 3R from 4R tauopathies, or staging Lewy pathology) rests on immunohistochemistry and the anatomic distribution of lesions, not on a single inclusion seen in isolation. Read the morphology back against the clinical syndrome, the regional pattern, and the immunostain before committing to a diagnosis.