Lewy body dementia is a complex brain disorder that affects thinking, movement, behavior, mood, and basic body functions. Because its early signs can resemble Alzheimer’s disease, Parkinson’s disease, or even mental health conditions, many families struggle for years before getting answers. Understanding the causes, symptoms, and diagnosis of Lewy body dementia can make it easier to recognize early changes, seek specialized care, and plan for the future.

At the center of Lewy body dementia are tiny protein deposits in the brain called Lewy bodies. These clumps are made of a protein called alpha-synuclein, which normally helps nerve cells communicate at the synapse. In Lewy body dementia, alpha-synuclein starts to form abnormal clumps inside neurons in particular brain regions. Over time, this disrupts chemical signaling, reduces the function of brain cells, and eventually leads to cell death and widespread damage.

Lewy bodies can affect many parts of the brain. The cerebral cortex, which supports thinking, language, and perception, may be involved, leading to changes in problem solving and visual understanding. The limbic cortex, which is important for emotions and behavior, can be affected, contributing to mood changes. The hippocampus, essential for forming new memories, may also be involved, which contributes to memory problems as the disease progresses. Regions that control movement, such as the midbrain and basal ganglia, often explain the slowed movement and stiffness some people experience. Even the brainstem, which helps regulate sleep and alertness, and the olfactory pathways that allow people to recognize smells, can be affected. Nerves outside the brain, such as those in the intestines, heart, and other organs, may also show changes that lead to constipation, dizziness upon standing, sexual dysfunction, or drooling.

Causes

Researchers do not yet know the precise cause of Lewy body dementia. They do know that Lewy body buildup is associated with the loss of neurons that use important neurotransmitters. Two major chemical messengers involved are acetylcholine, which supports memory and learning, and dopamine, which influences movement, thinking, motivation, sleep, and mood. When neurons that use these chemicals are lost, many of the hallmark symptoms of Lewy body dementia appear.

Age is considered the strongest known risk factor for Lewy body dementia, with most people developing symptoms after age 50. More men than women appear to be affected. Certain health conditions are associated with higher risk, including REM sleep behavior disorder and loss of smell. While some families with dementia with Lewy bodies show specific genetic variants, Lewy body dementia is usually not considered hereditary, and in most cases the cause is unknown. There is currently no genetic test that can accurately predict who will develop the disease. Studies suggest that a generally healthy lifestyle that includes physical activity, mental stimulation, and nutritious eating may support brain health in later life, although no specific habit is known to prevent Lewy body dementia.

Symptoms

Symptoms of Lewy body dementia can involve cognition, movement, sleep, behavior, and the automatic body functions people usually do not think about. Cognitive changes often begin with dementia that affects attention, visual-spatial skills, reasoning, and executive functions such as multitasking and planning. Memory may be relatively preserved at first, then gradually becomes more affected. People can have trouble judging distances, misidentify objects, or struggle with time, place, and numbers. Cognitive fluctuations are another distinctive feature. A person may be alert and engaged one day, then lethargic, confused, or staring into space the next. At times, ideas can seem disorganized or illogical. These ups and downs can be subtle and may be missed unless someone is watching closely over time.

Visual hallucinations are common in Lewy body dementia, often appearing early. They are usually detailed and realistic, such as seeing people, children, or animals that are not actually present. Hallucinations involving other senses, such as hearing, can also occur. Some hallucinations are not distressing and may not require treatment. Others can be frightening or provoke unsafe behavior for example, if a person attempts to confront a perceived intruder that is not real and in those situations medical treatment may be considered.

Movement symptoms are quite variable. Some people have very mild issues at first, while others show noticeable Parkinson-like changes early on. These can include slowed movement, rigid or stiff muscles, a shuffling walk, a frozen stance, tremor at rest, stooped posture, balance problems, falls, smaller handwriting, reduced facial expression, difficulty swallowing, and a weaker voice. In some cases of dementia with Lewy bodies, movement problems never become pronounced, which can make diagnosis even more challenging.

Sleep disorders are another common, but often overlooked, part of Lewy body dementia. REM sleep behavior disorder can appear years before any cognitive changes. People with this condition may talk, shout, kick, punch, or fall out of bed as if they are acting out vivid dreams, often involving threats or attacks. Excessive daytime sleepiness, where someone sleeps two or more hours during the day, insomnia, and restless leg syndrome can also be present. Because these sleep conditions are sometimes treatable, involving a sleep specialist can be an important part of the care plan.

Behavioral and mood changes may include depression, apathy, anxiety, agitation, delusions, paranoia, and hallucinations. A person may withdraw from activities they once enjoyed, ask the same questions repeatedly, become fearful when a familiar caregiver is not nearby, or develop firm but false beliefs such as thinking a spouse is unfaithful or that long-deceased relatives are still alive. Capgras syndrome, in which a person believes a loved one has been replaced by an identical imposter, can occur and is particularly distressing for families.

There are also symptoms tied to the autonomic nervous system, which controls functions such as blood pressure, temperature, sweating, and bladder control. People with Lewy body dementia may experience dizziness or fainting related to blood pressure changes, difficulty regulating body temperature, frequent falls, constipation, urinary incontinence, sexual dysfunction, sensitivity to heat or cold, and a poor sense of smell.

Diagnosis

There are two related diagnoses under the umbrella of Lewy body dementia. Dementia with Lewy bodies is characterized by early changes in thinking, attention, visual perception, and executive function, often accompanied by visual hallucinations, cognitive fluctuations, REM sleep behavior disorder, and later movement problems such as rigidity or tremor. Parkinson’s disease dementia refers to cognitive decline that develops more than a year after established Parkinson’s movement symptoms. Not everyone with Parkinson’s disease will develop dementia, and researchers are still working to understand who is most at risk. Over time, both forms of Lewy body dementia can lead to similar patterns of impairment because Lewy bodies are present throughout the brain, although the pace of change may vary.

Getting an accurate diagnosis of Lewy body dementia can take time. Many physicians are not deeply familiar with the condition, and early symptoms can mimic other disorders. A diagnosis usually begins with a visit to a primary care doctor, who may refer the person to a neurologist. Specialists such as movement disorder neurologists, cognitive and behavioral neurologists, geriatric psychiatrists, geriatricians, and neuropsychologists can all play important roles. Because no single test can confirm Lewy body dementia during life, clinicians rely on a combination of approaches, including a detailed medical history, physical and neurological examination, blood tests to rule out other conditions, brain imaging such as CT, MRI, or certain PET scans, and formal neuropsychological testing that evaluates memory, attention, language, and problem solving.

Sleep studies may be used to diagnose conditions like REM sleep behavior disorder, which can support the diagnosis. At present, Lewy body dementia can be confirmed with certainty only by brain autopsy after death, although researchers are actively searching for reliable biomarkers that might allow for more precise diagnosis during life.

Treatment

Although there is no cure yet, early diagnosis offers tangible benefits. It allows people to receive more appropriate treatment, avoid medications that may worsen symptoms, plan medical and caregiving needs, organize legal and financial affairs, and build a support network. It also provides an opportunity to consider participation in Lewy body dementia clinical trials that aim to understand genetics, brain changes, and potential new therapies. For caregivers and loved ones, a clear diagnosis can bring some relief by naming what is happening and providing a path forward.

Research into Lewy body dementia is moving steadily forward. Scientists are investigating biomarkers, exploring differences between dementia with Lewy bodies and Parkinson’s disease dementia, and examining the biology, genetics, and environmental influences that contribute to risk. Volunteers with and without Lewy body dementia are needed to participate in this work. While progress takes time, the ultimate goals are earlier and more accurate diagnosis, better symptom management, improved quality of life, and eventually ways to prevent or cure this challenging condition. Read more at https://www.nia.nih.gov/health/lewy-body-dementia/lewy-body-dementia-causes-symptoms-and-diagnosis