Lewy Body Dementia

What it is

Lewy body dementia is caused by tiny abnormal protein deposits, called Lewy bodies, building up in brain cells. It is closely related to Parkinson's disease, which involves the same deposits, and the two conditions overlap. Lewy body dementia is one of the more common causes of dementia, yet it is often missed or mistaken for Alzheimer's disease or Parkinson's disease, partly because its mix of symptoms is less familiar.

It has a distinctive combination of features: thinking and alertness that fluctuate markedly from hour to hour or day to day, recurrent and often detailed visual hallucinations, movement changes like those of Parkinson's disease, and a sleep disturbance in which people physically act out their dreams. Recognising this particular cluster matters not only for understanding but for safety, because of how the condition reacts to certain medicines.

What it can look like

Memory may be relatively preserved early on, while attention, alertness and visual-spatial abilities are affected, and the fluctuation is striking: the person can seem clear and capable at one moment and deeply confused or drowsy soon after, which families sometimes misread as the person "putting it on." Visual hallucinations are common and typically detailed, often of people or animals, and are not necessarily frightening. Movement changes resemble Parkinson's disease: stiffness, slowness, a shuffling walk, tremor, and a tendency to fall. Many people also act out their dreams in sleep, sometimes years before other symptoms (see our REM sleep behaviour disorder entry). Mood changes and sensitivity are common.

How common is it

Lewy body dementia is among the more common dementias after Alzheimer's and vascular dementia, though its true frequency is likely underestimated because of how often it is misdiagnosed. It generally affects older adults and is somewhat more common in men.

What causes it

The cause is the accumulation of Lewy bodies, the same protein deposits found in Parkinson's disease, in the brain. Why this happens is not fully understood, and for most people there is no clear inherited cause. Its close biological relationship to Parkinson's disease explains the shared movement symptoms and the overlap between the conditions.

How it is diagnosed

Diagnosis is clinical and best made by a specialist, based on recognising the characteristic combination: fluctuating cognition and alertness, recurrent visual hallucinations, Parkinson's-like movement features, and dream-enactment in sleep. An account from family of these features is invaluable. Specialised scans can support the diagnosis. Distinguishing it from Alzheimer's and Parkinson's disease matters because management, and especially medication safety, differs.

How it is treated, and a vital safety warning

There is no cure, but symptoms can be managed and quality of life supported, and getting the approach right is especially important here because of a serious safety issue. Many people with Lewy body dementia have severe, sometimes life-threatening reactions to certain antipsychotic medicines, the kind sometimes given for hallucinations or agitation. For this reason, these medicines must be avoided or used only with great caution and specialist oversight, and any family caring for someone with this diagnosis should make sure every treating clinician knows about it. This single fact is one of the most important reasons to diagnose the condition correctly.

Beyond this, some medicines used in Alzheimer's disease can help the thinking symptoms, careful management can address the movement problems and the sleep disturbance, and the hallucinations may not need treatment if they are not distressing. The supportive and caregiver guidance in our Alzheimer's and dementia entry applies here too, with the added emphasis on medication safety.

Lewy body dementia in the African context

Lewy body dementia is widely unrecognised even where services exist, and in many settings here its mix of memory problems, visual hallucinations, and movement changes is especially likely to be understood as bewitchment, madness, or normal ageing rather than a brain disease. This matters greatly because of a specific danger: people with this condition can react severely, even dangerously, to certain common antipsychotic medicines, so any psychotic-seeming symptoms must be told to a doctor who knows the diagnosis, not treated blindly. Awareness, among families and health workers alike, can be lifesaving. See the safety warning above.

Support for families and carers

Caring for someone with Lewy body dementia has particular challenges, and support matters.

• Make sure every health worker knows the diagnosis, because of the serious risk from certain antipsychotic medicines.
• Respond calmly to hallucinations, reassuring rather than arguing, and keep the environment well lit and familiar.
• Guard against falls, given the movement and alertness changes, and keep routines steady.
• Share the load and seek support, since the fluctuating symptoms are demanding. Our Get Support page can help.
• Look after your own health and rest.