Yes. Alzheimer’s disease and Lewy body dementia can occur in the same person because Alzheimer’s-related brain changes and Lewy body pathology can coexist. Clinicians and researchers commonly describe this as mixed dementia or co-pathology, not as a new combined FDA diagnosis. For example, a person may have progressive memory loss associated with Alzheimer’s disease while also experiencing recurrent visual hallucinations, fluctuating alertness, and movement changes associated with dementia with Lewy bodies.
The underlying proteins differ. Alzheimer’s disease pathology includes beta-amyloid plaques and tau tangles, while Lewy bodies are clumps of alpha-synuclein. The National Institute on Aging reports that Alzheimer’s pathology commonly occurs alongside Lewy bodies, but a diagnosis made during life may not reveal every process affecting the brain. Definitive confirmation of Lewy body pathology still requires examination of brain tissue after death, although diagnostic tests and biomarker research are improving.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- Can Alzheimer’s and Lewy Body Dementia Occur Together?
- How Common Is Alzheimer’s and Lewy Body Co-Pathology?
- Symptoms That May Suggest Dementia With Lewy Bodies
- How Doctors Evaluate Possible Mixed Dementia
- Treatment Challenges When Both Pathologies Are Suspected
- What Co-Pathology May Mean for Prognosis
- Why the Clinical Label May Change Over Time
- Frequently Asked Questions
Can Alzheimer’s and Lewy Body Dementia Occur Together?
Alzheimer’s disease and Lewy body disease are distinct disorders, but their biological boundaries are not always tidy. According to the National Institute on Aging, beta-amyloid plaques and tau tangles commonly coexist with Lewy bodies. A person can therefore meet clinical criteria for one form of dementia while carrying pathology associated with both. “Mixed dementia” is an umbrella description rather than a single, newly recognized disease.
It can refer to Alzheimer’s disease occurring with Lewy body pathology, vascular brain injury, or other neurological changes. By comparison, a clinical diagnosis such as probable dementia with Lewy bodies describes the pattern doctors observe; co-pathology describes what is happening biologically in the brain. The distinction matters in real life. Two people diagnosed with Alzheimer’s disease may both forget appointments, but one might also see detailed images of people who are not present, act out dreams, and develop stiffness or a shuffling gait. Those additional features can prompt an evaluation for Lewy body dementia even if Alzheimer’s-related changes remain part of the clinical picture.
How Common Is Alzheimer’s and Lewy Body Co-Pathology?
Autopsy research indicates that co-pathology is frequent, but there is no single percentage that applies to everyone. In an NIA-funded National Alzheimer’s Coordinating Center autopsy sample, 741 of 852 people with lewy body disease pathology—87%—also had Alzheimer’s neuropathologic change. The full study included 2,433 people and was published in the Journal of Alzheimer's Disease in 2021. That 87% figure should not be treated as the prevalence among all people with Lewy body dementia.
The participants came from a selected autopsy and research cohort, which may differ from patients seen in community medical practices. Referral patterns, age, pathology definitions, disease severity, and willingness to participate in brain-donation programs can all influence the result. A 2024 review of comorbid pathology in dementia with Lewy bodies illustrates this limitation. Across different studies, intermediate or high Alzheimer’s neuropathologic change was reported in 28% to 89% of dementia with Lewy bodies cases. The broad range reflects differences in cohorts and pathology thresholds, so presenting one rate without its study context can be misleading.
Symptoms That May Suggest Dementia With Lewy Bodies
Alzheimer’s disease and dementia with Lewy bodies can both cause declining judgment, memory problems, confusion, and difficulty completing daily tasks. Early Alzheimer’s disease often has a prominent effect on the ability to learn and retain new information. Early dementia with Lewy bodies may affect attention, visual-perceptual skills, and executive function more noticeably than memory. Core features that point toward dementia with Lewy bodies include marked fluctuations in cognition or alertness, recurrent well-formed visual hallucinations, REM sleep behavior disorder, and parkinsonism. Parkinsonism can include slowed movement, stiffness, tremor, or a shuffling gait.
Lewy body disease may also affect behavior, mood, sleep, and autonomic functions such as blood pressure regulation, digestion, and bladder control. These features are described by the National Institute on Aging and the DLB Consortium consensus report. Consider someone who forgets recent conversations but also has episodes in which they shift from clear conversation to pronounced confusion within the same day. If that person repeatedly sees children or animals that are not present and has begun punching or shouting while dreaming, the overall pattern deserves more than a routine memory assessment. Hallucinations can also result from medications, vision problems, delirium, or psychiatric illness, so they should not be assumed to prove Lewy body dementia by themselves.
How Doctors Evaluate Possible Mixed Dementia
Evaluation usually begins with a detailed medical history, neurological examination, cognitive testing, medication review, laboratory studies, and structural brain imaging. A clinician may ask a family member to keep a record of hallucinations, sleep behaviors, falls, movement symptoms, and changes in alertness. Specific observations—such as confusion consistently worsening after poor sleep—are often more useful than a general statement that the person has “good days and bad days.” No single scan or medical test can definitively diagnose Lewy body dementia during life, according to the National Institute on Aging. Certainty currently requires a brain autopsy after death. Alzheimer’s biomarker tests can identify evidence of amyloid or tau biology during life, but a positive Alzheimer’s biomarker does not rule out accompanying Lewy body pathology.
Conversely, the absence of a definitive Lewy body biomarker does not establish that Lewy bodies are absent. DaTscan, or ioflupane I-123 injection, is an FDA-approved adjunct to other evaluations in adults with suspected dementia with Lewy bodies. It visualizes dopamine transporters in the striatum and can support the distinction between a degenerative parkinsonian process and some alternative explanations. The tradeoff is that DaTscan is not a standalone diagnostic test: an abnormal result can support the clinical assessment, but it cannot independently prove dementia with Lewy bodies or map every coexisting pathology. The FDA prescribing information was revised in April 2026.
Treatment Challenges When Both Pathologies Are Suspected
Treatment is generally organized around the person’s symptoms, function, safety risks, and other medical conditions rather than an assumed pathology label alone. Cognitive symptoms, parkinsonism, sleep disturbance, depression, constipation, dizziness, and hallucinations may each require separate consideration. Non-drug measures—consistent routines, fall prevention, sleep assessment, vision correction, and caregiver education—can be important because adding medications may create competing effects. No FDA-approved drug specifically treats dementia with Lewy bodies itself.
The National Institute on Aging notes that rivastigmine is approved for cognitive symptoms in Parkinson’s disease dementia, which is a form of Lewy body dementia, but not for dementia with Lewy bodies generally. Other Alzheimer’s drugs may be prescribed for symptomatic treatment, depending on the individual situation. Medication sensitivity is a significant warning in suspected Lewy body dementia. Some antipsychotic medicines can cause severe adverse reactions, including pronounced rigidity, confusion, sedation, or potentially life-threatening complications. Hallucinations do not always require medication if they are nonthreatening, but sudden or distressing changes require medical assessment for infection, dehydration, pain, medication effects, or delirium before they are attributed to dementia progression.
What Co-Pathology May Mean for Prognosis
A 2024 review in the Journal of Neurology found that Lewy body disease with Alzheimer’s co-pathology was associated with a faster disease course, a greater risk of cognitive decline, and a poorer overall prognosis. These are group-level associations, not reliable forecasts for a particular individual.
Age, overall health, vascular injury, symptom pattern, and the amount and location of pathology can all influence progression. For example, one person with both pathologies may lose independence relatively quickly, while another may remain able to dress, eat, and participate in familiar activities for a longer period. Families can obtain more useful planning information by tracking concrete changes—such as new falls, missed medications, nighttime wandering, or help needed with finances—than by relying on an average survival or decline estimate from a research cohort.
Why the Clinical Label May Change Over Time
The diagnosis recorded in a medical chart may evolve as new symptoms emerge. A person initially diagnosed with Alzheimer’s disease may later develop parkinsonism, REM sleep behavior disorder, cognitive fluctuations, or detailed visual hallucinations that support probable dementia with Lewy bodies. Another person may receive an initial Lewy body dementia diagnosis and later have Alzheimer’s biomarkers that suggest significant co-pathology.
This change does not necessarily mean the original clinician made an obvious mistake. Mixed pathology can produce an incomplete or atypical symptom pattern, and current testing cannot disclose every underlying disease process. The NIA’s Lewy body dementia biomarker-development program runs through 2031, reflecting the continuing need for reliable living-person tests that can detect and monitor Lewy body disease.
Frequently Asked Questions
Is mixed Alzheimer’s and Lewy body dementia a separate FDA diagnosis?
No. Mixed dementia and co-pathology are descriptive terms indicating that more than one disease process may be present. They do not constitute a new combined FDA diagnosis.
Can a person have Alzheimer’s pathology without typical Alzheimer’s symptoms?
Yes. Brain pathology and clinical symptoms do not always correspond perfectly. Alzheimer’s-related amyloid and tau changes may coexist with a symptom pattern dominated by Lewy body disease.
Do visual hallucinations prove that someone has Lewy body dementia?
No. Recurrent, well-formed visual hallucinations are an important feature of dementia with Lewy bodies, but medications, delirium, impaired vision, psychiatric conditions, and other neurological disorders can also cause hallucinations.
Can DaTscan confirm mixed dementia?
No. DaTscan is an adjunctive test that may support an evaluation for suspected dementia with Lewy bodies. It cannot definitively diagnose Lewy body dementia or determine whether Alzheimer’s pathology is also present.
Can mixed Alzheimer’s and Lewy body pathology be confirmed while a person is alive?
Alzheimer’s biomarkers can provide evidence of Alzheimer’s-related biology during life, but there is currently no single medical test that definitively confirms Lewy body dementia. Definitive confirmation of Lewy body pathology still requires brain examination after death.
