The DSM-5 has replaced terms like mild cognitive impairment and dementia with the term neurocognitive disorder. There are two major types of neurocognitive disorders diagnosed in the DSM-5.
- Mild neurocognitive disorder is diagnosed when there is some type of impairment in cognition (thinking) that is recognized by the person or some other knowledgeable source (family member, friend, etc.). There also must be evidence on testing that the person has a decline in their thinking abilities, such as memory, language abilities, reasoning, etc. Even though the person has shown some form of decline in their thinking, this decline is not significant enough to interfere with their daily routine and activities.
- Major neurocognitive disorder is diagnosed when the person demonstrates a decline in their cognition as described above and this change in thinking abilities results in significant issues with their ability to function in their daily routine. For example, they need outside help to do things or no longer do them at all, such as remembering things, that they used to be able to do without help.
Most often, but not always, a person diagnosed with a mild neurocognitive disorder does not have dementia. Instead, they are considered to have what used to be termed Mild Cognitive Impairment or MCI. A diagnosis of a major neurocognitive disorder indicates that they most likely have some form of dementia. Depending on the severity of the symptoms, the diagnosis of what many still refer to as Lewy Body Dementia or some similar term is used. It is then referred to as a Minor Neurocognitive Disorder with Lewy Bodies or a Major Neurocognitive Disorder with Lewy Bodies.
What are Lewy bodies?
Lewy bodies get their name from the researcher that first described them, Friedrich H. Lewy. They are abnormal clumps of protein that may develop inside the nerve cells in the brain and spinal cord. These nerve cells are referred to as neurons. For the neurons to communicate with each other and for a person to perform all the necessary functions to think, move, etc. their neurons need to be able to release chemical messengers known as neurotransmitters.
Neurotransmitters are the substances that allow the nerve cells in the brain to communicate with each other. When Lewy bodies develop within many neurons, there can be problems with the communication between neurons due to a lack of neurotransmitters (these chemical messengers). This situation can result in several different brain disorders including Lewy body dementia and Parkinson's disease. Lewy bodies are also present in many people who have no diagnoses of dementia. They are often present in people who are diagnosed with Alzheimer's disease, and may be present in people with other neurocognitive disorders.
At the time of this writing, there are no specific risk factors associated with the development of Lewy body dementia other than the finding that it is far more common in elderly people than it is in younger people. Thus, getting older increases the risk to develop Lewy body dementia or some other form of a neurocognitive disorder.
Prevalence of a Lewy Body Dementia
The DSM-5 reports that in all elderly people the prevalence of a neurocognitive disorder with Lewy bodies is 0.1% to 5%. The prevalence in the group of people who are diagnosed with some form of dementia is higher and is reported as 1.7% - 30.5%. The prevalence of dementia increases with age meaning that people who are between the ages of 65-70 have a lower chance of a dementia diagnosis than people who are between 80-85. In general, it can be estimated that about 14% of all people over the age of 65 are diagnosed with some form of dementia. For every case where Lewy body dementia is diagnosed in a female there are 1.5 cases diagnosed in males.
Lewy body dementia is diagnosed when specific criteria are met, and dementia is suspected. Not everyone with Lewy bodies in their brain develops Lewy body dementia. Lewy bodies are commonly found in the brain tissue of elderly people when autopsies are performed. When brain tissue is analyzed in people who have been diagnosed with dementia it appears that between 20 - 35% of dementia cases have Lewy bodies in their brain and/or spinal cord.