Lewy Body Dementia: How Is It Different From Alzheimer's?

Lewy body dementia and Alzheimer's disease both cause memory and thinking problems, but they often start differently. Lewy body dementia is more often associated with vivid visual hallucinations, big swings in alertness, acting out dreams during sleep, and Parkinson-like stiffness or slowness. Alzheimer's more often begins with trouble forming new memories. This article compares the two, explains why diagnosis can be hard, covers medication cautions, and lists when symptoms need urgent care.

Lewy body dementia vs. Alzheimer's: the short comparison

Both conditions are progressive brain diseases that can affect memory, thinking, mood and daily function. They also overlap. Many people have features of both, and the brain changes of one can occur alongside the other. Because of this, the comparison below describes patterns that are often seen, not rules that fit every person.

MedlinePlus, from the National Institutes of Health, describes Lewy body dementia as a disease linked to abnormal deposits of a protein called alpha-synuclein in the brain. These deposits are called Lewy bodies. Alzheimer's disease is more closely associated with different protein changes, including amyloid and tau. How these changes cause symptoms is not fully understood, and several factors probably contribute.

How the early symptoms differ

Memory versus attention and visual processing

In Alzheimer's disease, a common early sign is difficulty remembering recent conversations or events. In Lewy body dementia, memory may be better preserved early on, while attention, problem solving and judging distances or shapes can be affected. A person may get lost in a familiar room, misjudge stairs or struggle to follow a TV plot even though they can recall recent events reasonably well.

These are patterns, not tests. Plenty of people with Alzheimer's have visual-spatial trouble, and plenty of people with Lewy body dementia have significant memory loss as the illness advances.

Fluctuating alertness

One feature often described in Lewy body dementia is unpredictable change. A person may be sharp and chatty in the morning, then staring, drowsy or confused in the afternoon. Family members sometimes describe it as "good days and bad days" that can even occur within the same day. Daytime sleepiness, long staring spells and disorganized speech can be part of this picture. A person who is very hard to wake, or who cannot be roused, is a different situation from the usual ups and downs and needs emergency care.

Evening worsening is a separate topic that can occur in many kinds of dementia. Our article on sundowning covers that pattern.

Visual hallucinations

Seeing things that are not there is one of the features clinicians look for in Lewy body dementia. People often describe well-formed images, such as children, small animals or strangers in the house. Early on, the person may know the images are not real. Later, they may be frightened or convinced that the images are real, which can be distressing for everyone.

Hallucinations can also come from infections, medication side effects, vision problems or delirium, so a new hallucination deserves a medical review and should not be assumed to be dementia. The difference between a sudden confusional state and a gradual dementia is covered in our article on delirium vs. dementia.

Movement, sleep and body symptoms

Lewy body dementia is closely related to Parkinson disease, and the two share the same kind of protein deposits. MedlinePlus lists movement features such as stiffness, slowness, tremor, a shuffling walk and balance problems among the symptoms of Lewy body dementia. Falls can be a particular concern.

Sleep and autonomic changes are also reported. These can include:

• Acting out dreams by shouting, kicking or punching during sleep, which may appear years before memory or thinking changes.
• Daytime drowsiness and long naps.
• Lightheadedness or fainting when standing up, which can reflect blood pressure changes.
• Constipation, bladder problems and a reduced sense of smell.

None of these alone establishes Lewy body dementia. They are common in older adults for many reasons, including medications and other conditions. If walking trouble, memory change and bladder leaks occur together, a different treatable condition is also worth considering, as described in our article on normal pressure hydrocephalus.

Why the diagnosis is hard, and how clinicians approach it

Lewy body dementia is often confused with Alzheimer's disease, Parkinson disease or a psychiatric illness, particularly in the early stages. There is no single test that settles the question. Clinicians combine the history from the person and a family member, a neurological examination, cognitive testing, a review of medications, blood tests and brain imaging to look for other causes.

The Alzheimer's Association clinical practice guideline on diagnostic evaluation of suspected Alzheimer's disease and related disorders describes a structured approach to assessment in specialty care. Biomarker tests, such as spinal fluid or specialized blood measurements of amyloid, can support an Alzheimer's diagnosis in some situations, but they do not exclude Lewy body changes, and mixed disease is common. A systematic review of Alzheimer's disease diagnostic testing guidelines shows that recommendations vary and that testing is meant to support a clinician's judgment.

Research comparing the two diseases at the molecular level, such as a proteomic comparison of Alzheimer's and Lewy body dementias, finds both shared and distinct protein patterns. That work helps explain why the illnesses overlap, and it is not yet a routine bedside test.

A neurologist, geriatrician or memory clinic with experience in dementia can be especially helpful when the picture is unclear. Bringing a written list of symptoms, when they began, what medications are taken and any episodes of hallucinations, falls or dream enactment makes the visit more useful.

Why the right label matters for treatment

Treatment is aimed at symptoms. Outcomes vary, and current treatments aim to ease symptoms rather than reverse either disease. The reason for sorting out which condition is more likely is largely about safety.

Antipsychotic medicines need special care

People with Lewy body dementia may be more likely to have severe, sometimes dangerous reactions to some antipsychotic medicines, particularly older ones such as haloperidol. These reactions can include sudden worsening stiffness, marked confusion, sedation or falls. Antipsychotic labels also carry a boxed warning about increased risk of death in older adults with dementia-related psychosis. Because of these cautions, tell every clinician, emergency department, hospital team and pharmacist that Lewy body dementia is present or being considered. Do not stop, start or change any prescription on your own; ask the prescriber how to handle troubling behaviors or hallucinations.

Cholinesterase inhibitors and other medicines

Medicines used for Alzheimer's disease, such as donepezil, are also used in Lewy body dementia, and some people see benefit in thinking, alertness or hallucinations. Responses differ from person to person. Our article on donepezil and memantine explains what these drugs can and cannot do. Clinicians may also treat related problems such as movement symptoms, low blood pressure on standing, sleep disorders and mood changes, each with its own risks and benefits to discuss with the prescriber.

Surgery, anesthesia and hospital stays

Hospitalization, infections and some sedating or anticholinergic medicines, including diphenhydramine found in many over-the-counter sleep aids, can worsen confusion in people with dementia. Mention the diagnosis, or the suspicion of it, before any procedure so the care team can choose medicines carefully.

Safety at home

• Reduce fall hazards: clear walkways, secure rugs, add handrails and good lighting.
• If dream enactment occurs, ask the clinician about making the bedroom safer, such as padding sharp furniture edges and moving objects away from the bed.
• When hallucinations happen, respond calmly. Arguing about whether the image is real often increases distress. Tell the clinician about new or worsening hallucinations so they can look for a cause.
• Keep an up-to-date medication list, including over-the-counter sleep aids and allergy medicines, and review it with the prescriber or pharmacist.
• Support for the caregiver matters as well. Local aging agencies and dementia support groups can help.

For an overview of the many kinds of dementia, MedlinePlus has a general page on dementia. If you are trying to separate ordinary forgetfulness from something more, see early signs of dementia vs. normal aging. Depression can also mimic dementia, as discussed in our pseudodementia article.

When to see a clinician about these symptoms

Book an appointment if a family member has new hallucinations, unexplained falls, dream enactment, fluctuating confusion, new slowness or stiffness, or memory and thinking changes that interfere with daily life. A sudden change in thinking or alertness is different: it can reflect infection, medication effects or another acute illness and needs prompt evaluation. Stroke signs, a person who is very hard to wake, and other emergencies are listed in the box below.

When to Seek Medical Care