Dementia with Lewy bodies

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Dementia with Lewy bodies is a nervous system disorder characterized by a decline in intellectual function (dementia), a group of movement problems known as parkinsonism, visual hallucinations, sudden changes (fluctuations) in behavior and intellectual ability, and acting out dreams while asleep (REM sleep behavior disorder). This condition typically affects older adults, most often developing between ages 50 and 85. The life expectancy of individuals with dementia with Lewy bodies varies; people typically survive about 5 to 7 years after they are diagnosed.

REM sleep behavior disorder may be the first sign of dementia with Lewy bodies. It can occur years before other symptoms appear. Individuals with REM sleep behavior disorder act out their dreams, talking and moving in their sleep when they should be still. This behavior becomes less pronounced as dementia with Lewy bodies worsens and additional features develop.

Dementia is often the second major feature to develop in dementia with Lewy bodies. Initially, this intellectual decline may be mild or seem to come and go. In this condition, dementia often leads to impaired ability to perform visual-spatial tasks such as assembling puzzles. Affected individuals may also have poor problem-solving skills (executive functioning), speech difficulties, and reduced inhibitions. Problems with memory typically do not occur until later.

Most people with dementia with Lewy bodies experience visual hallucinations, which often involve people or animals. Fluctuations in behavior and thought processes (cognition) include sudden changes in attention, unintelligible speech, and brief episodes of altered consciousness that may appear as staring spells.

Parkinsonism is usually the last major feature to develop in people with dementia with Lewy bodies, although it can appear earlier in some individuals. The movement problems typically include tremors, rigidity, unusually slow movement (bradykinesia), and impaired balance and coordination (postural instability). Affected individuals may require walking aids or wheelchair assistance over time.

Individuals with dementia with Lewy bodies may also experience a sharp drop in blood pressure upon standing (orthostatic hypotension), fainting episodes (syncope), reduced sense of smell, increased saliva production and drooling, difficulty controlling the flow of urine (incontinence), or constipation.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also called mutations) in genes known as SNCA and SNCB can cause dementia with Lewy bodies. The SNCA and SNCB genes provide instructions for making proteins, called alpha-synuclein and beta-synuclein, respectively, that are found primarily in the brain. Alpha-synuclein plays a role in communication between nerve cells (neurons), helping to regulate the release of chemical messengers (neurotransmitters). Beta-synuclein is likely involved in a process that allows neurons to change and adapt over time, which is necessary for learning and memory. Beta-synuclein may also prevent harmful accumulation of alpha-synuclein in neurons.

Variants in another gene called GBA1 or a certain version of a gene called APOE increase the risk of developing the condition, but are not a direct cause. The enzyme produced from the GBA1 gene is found throughout the body in cell structures called lysosomes that digest and recycle proteins and other materials that are no longer needed. The APOE gene provides instructions for making a protein, called apolipoprotein E, which packages cholesterol and other fats and carries them through the bloodstream.

Changes in these four genes can lead to the formation of Lewy bodies, which are clusters of alpha-synuclein protein. SNCA gene variants result in misshapen alpha-synuclein proteins that cluster together (aggregate). SNCB gene variants lead to the production of an altered beta-synuclein protein that allows accumulation of alpha-synuclein. GBA1 gene variants are thought to disrupt the normal function of lysosomes. Research suggests that malfunctioning lysosomes impair the breakdown of alpha-synuclein, increasing the risk of its accumulation and the formation of Lewy bodies. There are multiple versions of the APOE gene, one version, called the e4 allele, seems to increase an individual's risk for developing dementia with Lewy bodies, although the mechanism is unclear. It is thought that the apolipoprotein E produced from the e4 allele of the APOE gene may disrupt the transport of alpha-synuclein into and out of cells, leading to its accumulation.

In dementia with Lewy bodies, alpha-synuclein clusters accumulate inside and outside of neurons throughout the brain where they impair cell function and ultimately cause cell death. Neurons that produce the neurotransmitter dopamine seem to be particularly vulnerable to Lewy bodies. Dopamine has many important functions, including playing complex roles in cognition, motivation, behavior, and control of movement. Over time, the loss of dopamine-producing neurons can increasingly impair intellectual and motor function and the regulation of emotions, resulting in the signs and symptoms of dementia with Lewy bodies.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

When dementia with Lewy bodies is caused by SNCA or SNCB gene variants, it is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In these cases, an affected person usually has one parent with the condition.

People with a variant in one copy of the GBA1 gene or one copy of the APOE e4 allele inherit an increased risk of developing dementia with Lewy bodies, not the condition itself. Some people with these genetic variants never develop dementia with Lewy bodies. This increased risk is inherited in an autosomal dominant pattern.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Dementia with Lewy bodies is estimated to affect 1.4 million people in the United States. It accounts for about 5 percent of all dementia cases in older individuals and is the second most common dementia after Alzheimer's disease.

Which doctor should you see?

The suggested department for discussing Dementia with Lewy bodies is Neurology, with a neurologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which nervous-system findings help explain the symptoms?
• Would an assessment of walking, communication or daily function be helpful?
• Are rehabilitation or other specialist services relevant?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Dementia with Lewy bodies. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.