When the Wrong Diagnosis Gets in the Way: Lewy Body Dementia and Its Confusion with Alzheimer’s

Lewy body dementia (LBD) is the second most common form of progressive dementia after Alzheimer’s disease, yet it remains one of the most frequently misdiagnosed conditions in neurology.

Studies suggest that up to 80% of LBD cases are initially misdiagnosed, often as Alzheimer’s. This isn’t simply a matter of medical error — it reflects a genuine overlap in symptoms, shared patient demographics, and real limitations in current diagnostic tools. hy this confusion happens matters enormously, because the two conditions require different treatments, and some medications used for Alzheimer’s can be dangerous for people with LBD.

What is Lewy Body Dementia?

Lewy body dementia is caused by abnormal deposits of a protein called alpha-synuclein that form inside neurons. These deposits, called Lewy bodies, disrupt brain function progressively. Lewy body dementia includes two closely related conditions: dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD).

The distinction between these two is largely about timing — in DLB, cognitive symptoms appear before or alongside motor symptoms; in PDD, a person has had Parkinson’s disease for at least a year before dementia sets in.

What Alzheimer’s and LBD Share

The surface-level similarity between the two conditions is real. Both cause progressive cognitive decline, memory problems, confusion, and difficulty with daily tasks. Both typically appear in people over 65. Both involve neurodegeneration — the gradual death of brain cells — and both worsen over time without any currently available cure. When a patient walks into a clinic reporting memory loss, disorientation, and difficulty concentrating, the first assumption is often Alzheimer’s, simply because it is far more prevalent. This statistical bias alone accounts for a significant portion of misdiagnoses.

Where the Confusion Gets Deeper: Overlapping Pathology

The situation is made more complicated by the fact that many people with LBD also have Alzheimer’s pathology in their brains. Amyloid plaques and tau tangles — the hallmarks of Alzheimer’s — are found in a substantial proportion of LBD patients at autopsy.

This means that even if a clinician suspects something beyond Alzheimer’s, the biological evidence they might find can be mixed, muddying the picture further.

Additionally, LBD patients do experience memory problems. While memory loss in Alzheimer’s tends to be early, prominent, and relentless, LBD patients often show fluctuating cognition — they can seem relatively sharp one hour and severely confused the next. This fluctuation can actually lead clinicians to underestimate the severity of the condition or attribute the variation to other causes, delaying accurate diagnosis.

The Symptoms That Should Signal LBD — But Often Get Missed

LBD has several characteristic features that distinguish it from Alzheimer’s, but these are either not recognized or misattributed.

1. The most distinctive is recurrent visual hallucinations. In LBD, these are typically well-formed and detailed — patients often describe seeing people, animals, or objects that are not there. In Alzheimer’s, hallucinations do occur but are less common and usually appear later in the disease course. When a family member reports that their loved one is seeing things, the clinical instinct is sometimes to attribute this to psychosis or to a late stage of Alzheimer’s rather than reconsidering the diagnosis entirely.
2. REM sleep behavior disorder (RBD) is another major feature that often precedes LBD by years or even decades. In RBD, the normal muscle paralysis that occurs during dreaming fails, and people physically act out their dreams — shouting, kicking, or falling out of bed. This symptom is strongly associated with synucleinopathies (the family of diseases that includes LBD and Parkinson’s). It is not a feature of Alzheimer’s. Unfortunately, it is rarely asked about in standard cognitive assessments, and patients and families may not think to mention it.
3. Parkinsonism — the motor symptoms of stiffness, slowness, and shuffling gait associated with Parkinson’s disease — appears in most LBD patients, though not always early. When mild, this can be attributed to aging or dismissed. When more pronounced, it sometimes prompts a Parkinson’s diagnosis rather than LBD, particularly if cognitive decline is not yet severe.
4. Autonomic dysfunction is also common in LBD. This includes blood pressure drops upon standing (orthostatic hypotension), constipation, urinary incontinence, and difficulty regulating temperature. These symptoms are often treated individually as separate medical problems rather than recognized as part of a unifying diagnosis.

The Diagnostic Tools Problem

Alzheimer’s has benefited from decades of research into biomarkers. PET scans can detect amyloid and tau accumulation; cerebrospinal fluid tests can measure relevant proteins; and genetic testing for risk factors like APOE-e4 is available. LBD lacks equally accessible and standardized diagnostic markers in everyday clinical practice.

DaTscan — a type of imaging that assesses dopamine transporter activity in the brain — can support an LBD diagnosis by showing reduced dopamine activity, which is not seen in Alzheimer’s. However, this scan is not universally available, is expensive, and is not always ordered unless a clinician already has a strong suspicion of LBD. If the initial evaluation doesn’t raise that suspicion, the test simply isn’t requested.

Standard cognitive testing like the MMSE or MoCA doesn’t differentiate well between the two conditions. Both LBD and Alzheimer’s patients can score poorly on these tests, and the pattern of impairment — while different in detail — requires a more thorough neuropsychological examination to tease apart, which is not always performed in routine clinical settings.

Why the Misdiagnosis is Dangerous

This is where the stakes go beyond semantics. Antipsychotic medications are often prescribed for the hallucinations and behavioral symptoms that come with dementia.

In Alzheimer’s patients, these medications carry risks but are sometimes used with monitoring.

In LBD patients, typical and even some atypical antipsychotics can cause severe, life-threatening reactions — a condition known as neuroleptic sensitivity. Patients can develop extreme rigidity, high fever, and rapid cognitive decline. Deaths have been reported. A misdiagnosis of Alzheimer’s followed by a standard antipsychotic prescription is not a minor error — it can be fatal.

On the other side, cholinesterase inhibitors like rivastigmine, commonly used in Alzheimer’s, can actually help LBD patients with cognitive symptoms and may reduce hallucinations.

This means an LBD patient labeled as Alzheimer’s might still receive some benefit from that treatment, but the full picture of their condition — including which medications to absolutely avoid — remains invisible to their care team.

Why Diagnosis is Still Delayed on Average

Most research puts the average time from symptom onset to accurate LBD diagnosis at around 18 months to several years. Several factors sustain this delay. Awareness of LBD among general practitioners remains low compared to Alzheimer’s. The condition was not described and defined clearly in medical literature until the 1980s and 1990s, and its diagnostic criteria have been revised multiple times since. Many physicians who are not specialists in movement disorders or behavioral neurology may have limited exposure to LBD in training.

Patients and families also contribute to the delay unintentionally. Hallucinations are sometimes kept secret out of embarrassment or fear of being labeled as having a psychiatric condition. Sleep behaviors are dismissed as normal aging or not considered relevant to report. The fluctuating cognition that characterizes LBD can make family members doubt themselves — “but sometimes he seems perfectly fine” — rather than recognizing the fluctuation itself as a symptom.

What an Accurate Diagnosis Changes

Getting the right diagnosis does not currently change the ultimate trajectory of the disease — there is no cure for LBD — but it changes management in critical ways. Care teams can avoid dangerous medications. Patients and families can access disease-specific support resources and clinical trials. Prognosis can be discussed more accurately, since LBD often progresses more rapidly than Alzheimer’s. Planning for care needs can happen earlier and with more specificity.

There is also the matter of dignity and understanding. Patients who know their diagnosis can make sense of their hallucinations — understanding that they are a neurological symptom rather than a sign of madness. Families can better anticipate what lies ahead and prepare for it.

The Bottom Line

Lewy body dementia is misdiagnosed as Alzheimer’s largely because the two share core features of dementia in older adults, because diagnostic tools for LBD are less standardized and accessible, and because clinical awareness of LBD’s distinguishing symptoms remains inconsistent.

The condition is not rare — it accounts for somewhere between 10 and 15 percent of all dementia cases — and its misdiagnosis carries real, sometimes life-threatening consequences. Better outcomes depend on clinicians routinely asking about hallucinations, sleep behaviors, and motor symptoms in dementia evaluations, and on expanding access to imaging and biomarker tests that can clarify the underlying diagnosis before treatment decisions are made.

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