Although it is not as familiar to the public as Alzheimer's Disease or Vascular Dementia, Lewy Body Dementia (LBD) is one of the second most common types of dementia (along with Vascular Dementia). Even though this type of dementia was first identified in the 1980s, it does not currently appear in the DSM-IV. Therefore, a person with LBD currently receives a DSM diagnosis of "Dementia Due to Lewy Bodies," which fits into the category "Dementia Due to Other General Medical Conditions." Lewy Body Dementia is sometimes referred to as Lewy Body Disease, Diffuse Lewy Body Disease, or Cortical Lewy Body Disease.
Prevalence statistics describing Lewy Body Dementia are somewhat unclear, primarily because Lewy bodies - the hallmark of this disorder - are associated with several different diseases. This makes it difficult to distinguish LBD from other conditions. Keeping this problem in mind, the Lewy Body Dementia Association reports that up to 20% of all dementia cases are from LBD (over 800,000 people in the United States). The disease appears to affect slightly more men than women.
Lewy Body Dementia is characterized by deposits of a misfolded protein called alpha-synuclein inside neurons (the primary cells in the brain and spinal cord). The protein deposits are called "Lewy bodies" after Friederich H. Lewy, the researcher who first described them in the early 1900s. How or why these deposits develop in the first place is unknown.
Lewy bodies that form in the brain stem and the rest of the brain decrease the amount of available dopamine and acetylcholine. Both of these chemicals are neurotransmitters (chemical messengers in the brain and nervous system) which work together so that messages controlling motor movement are properly sent and received. These deficits in neurotransmitters cause movement problems referred to as "Parkinsonian" symptoms (described below), as well as disrupting memory, learning, perception, thinking, and behavior.
Interestingly, Lewy bodies are also found in the brains of those with Parkinson's Disease and - sometimes - even Alzheimer's Disease, making diagnosing all of these illnesses much more complicated.
Age is the only definitive risk factor for Lewy Body Dementia. A person's risk for developing this type of dementia increases as age increases, with most cases occurring between the ages of 50 and 85. Sometimes, LBD runs in families, but for the most part, the disease occurs in people with no family history of the disorder.
As described in more detail below, some researchers also consider REM Sleep Behavior Disorder a significant risk factor for developing Lewy Body Dementia.