# Proof Narrative: Co-occurrence of Lewy pathology and ADNC is common (≥30% of AD cases have LP; ≥50% of DLB cases have ADNC)

## Verdict

**Verdict: PROVED**

The neuropathology literature consistently supports that Alzheimer's and Lewy body pathologies frequently co-occur at the rates claimed.

## What was claimed?

The claim states that two of the most common neurodegenerative pathologies — Alzheimer's disease neuropathologic change (the plaques and tangles of Alzheimer's) and Lewy pathology (the protein clumps associated with Lewy body dementia and Parkinson's) — are found together in the brain far more often than many people realize. Specifically, at least 30% of people whose brains show Alzheimer's pathology at autopsy also have Lewy pathology, and at least 50% of people with dementia with Lewy bodies also have significant Alzheimer's pathology. This matters because mixed pathology is the rule rather than the exception in neurodegenerative disease, and it has real implications for diagnosis, treatment, and clinical trials.

## What did we find?

We examined eight independent sources from across the neuropathology literature, including large autopsy databases, peer-reviewed reviews, and academic research centers.

For the first part of the claim — that at least 30% of Alzheimer's cases have Lewy pathology — the strongest quantitative evidence comes from the National Alzheimer's Coordinating Center database, which studied 2,742 autopsy cases and found that 38% of participants with Alzheimer's pathology also had co-occurring Lewy body disease. A comprehensive review published in Alzheimer's & Dementia confirmed the high prevalence of coexisting pathologies. The Lewy Body Dementia Association, citing NACC autopsy data, described Lewy body pathology as "the most common co-existing pathology in people with Alzheimer's disease up to 80 years of age." A separate study from the University of British Columbia confirmed that Alzheimer's and Lewy body patients "frequently demonstrate coexistent" pathology at autopsy.

For the second part — that at least 50% of dementia with Lewy bodies cases have Alzheimer's pathology — the evidence is even more consistent. A 2023 review in Alzheimer's & Dementia explicitly states that AD co-pathology "is present in more than 50% of DLB individuals." The University of Pennsylvania's Neuropathology Lab reports that approximately 50% of all Lewy body disease cases have sufficient Alzheimer's pathology for a secondary diagnosis. The Mayo Clinic brain bank, reported in a 2025 Molecular Neurodegeneration paper, found comorbid Alzheimer's pathology in 59% of 363 Lewy body dementia patients. Even a Swedish biomarker study found 48% co-pathology rates, and this included milder cases that would dilute the DLB-specific rate.

## What should you keep in mind?

The rates vary depending on how studies are designed. Population-based samples (which include people with mild or preclinical disease) tend to find lower co-pathology rates — one study reported only 20% Lewy pathology in Alzheimer's cases. Clinic-based samples, which study patients who actually sought medical attention, find higher rates. The 30% threshold is well-supported in clinic-based and referral settings but less consistently in the general population.

The definition of "Lewy pathology" also matters. If you only count Lewy bodies in the cortex (the most severe form), rates are lower. If you include amygdala-predominant Lewy pathology (a milder, widely recognized form), rates are higher. The claim does not restrict to cortical distribution, which is appropriate given current neuropathological classification standards.

A comprehensive forest plot across multiple studies estimated the overall rate of Alzheimer's comorbidity in Lewy body dementia at 37% — but this included Parkinson's disease dementia cases (which have lower co-pathology rates), pulling the average below the DLB-specific figure.

## How was this verified?

This claim was evaluated using the Proof Engine methodology, which requires every factual assertion to be backed by a verifiable citation or computation. Eight sources were consulted across both sub-claims, all citations were verified against their original source pages, and four adversarial checks searched for counter-evidence. The full analysis is available in [the structured proof report](proof.md), with verification details in [the full verification audit](proof_audit.md). You can [re-run the proof yourself](proof.py) to reproduce the results.
