The DSM-5 diagnostic criteria divide the neurocognitive disorders into two separate categories:
- mild neurocognitive disorder - means that the person has problems with memory or some other cognitive function. However, they do not have severe problems with thinking that interferes with their daily functioning. The person may be beginning to develop dementia, or the condition may not develop further at all.
- major neurocognitive disorder - having this diagnosis might qualify the individual as being diagnosed with a form of dementia. In this case, the person has significant problems with their thinking in at least one area that interferes with their ability to function daily.
There are many medical conditions that can cause major neurocognitive disorder (dementia). The DSM-5 lists several of these. It also recognizes that other medical conditions that are not specifically listed can also cause a major neurocognitive disorder/dementia. The specific medical causes of dementia listed in the DSM-5 include:
- progressive forms of dementia. These are when the damage that produces the dementia starts slowly and develops from a mild neurocognitive disorder to a major neurocognitive disorder over time.
- forms of dementia that may not be progressive
- forms that may be reversible.
Medical conditions listed in the DSM-5 that result in progressive dementias include:
Alzheimer's disease: Alzheimer's disease is the most common cause of dementia. The specific cause of Alzheimer's disease is not known, but the signs of Alzheimer's disease include plaques and tangles in the brain that interfere with the brain's ability to function. Plaques are clumps of protein (beta-amyloid) that form in the nerve cells or neurons in the brain. These plaques eventually cause the nerve cells to die. Tangles are made up of a protein called tau protein. In healthy cells the tau protein helps the cell to transport substances throughout the cell. However, when tangles form, nutrients and other important substances cannot move in the cell and the cell eventually dies. In Alzheimer's disease people most commonly begin having trouble remembering new information and as time goes on this difficulty becomes worse. People develop issues with other areas of thinking as the disease develops such as problems with language and reasoning.
Vascular disease: Dementia associated with vascular disease can happen from a stroke or because of the long development of blockages in the veins and arteries in the brain. The damage to the brain results from a lack of oxygen and nutrients to one or more areas of the brain that can result in difficulty with memory, communicating, moving, etc. The types of problems that the person experiences because of dementia caused by vascular disease depends on which areas of the brain are affected. The dementia that occurs from vascular disease can be progressive or if it is treated may not change. When the disease is progressive, people often have what is referred to as a "stepwise decline." When the vascular disease causes damage, they have a very rapid decline in their thinking. After this rapid decline the person's cognitive problems remain steady for a while at that lower level. Then the person experiences further damage and another rapid decline in cognition happens. This pattern continues with periods of rapid decline and then remaining steady.
Lewy body disease: Lewy bodies are lumps of protein that develop in the brain cells. These abnormal clumps of protein interfere with the functioning of the brain cells and many of the cells will eventually die. If the person develops many Lewy bodies in their brain cells they may suffer Lewy body dementia. The DSM-5 lists the major symptoms of major neurocognitive disorder with Lewy bodies as being:
- A gradual change in the person's cognition (thinking abilities).
- Fluctuating changes in the person's attention and concentration where sometimes they show impairments and other times they don't.
- Visual hallucinations (seeing things that are not there).
- Symptoms that resemble Parkinson's disease that happen along with the cognitive changes.
Frontotemporal lobar degeneration: This category represents a group of diseases that are all identified by the breakdown of the nerves or neurons in the frontal lobes and temporal lobes of the brain (temporal means sides). People with this type of disease often do not experience significant problems with memory in the early stages, but display other symptoms first. The symptoms that first happen in these dementias are symptoms with a person's behavior, language abilities, or even changes in their personality. The DSM-5 reports that there are two major types of symptoms that happen in these forms of dementia. People diagnosed with this form of dementia will often have one of these major groups of symptoms that include:
- Behavioral symptoms: these are problems with restraining one's behavior or impulses, having major feelings of depression, a loss of being sympathetic to others, being very talkative but having speech that is relatively meaningless, and repetitive behaviors.
- Language symptoms: These symptoms include problems with expressing oneself, naming objects, or understanding language.
HIV infection: HIV or AIDS is a disorder of the immune system. The virus that causes HIV can also affect the brain. According to the DSM-5, a person diagnosed with a neurocognitive disorder that is believed to be due to an HIV infection would have to have a documented history of having HIV and their neurocognitive disorder could not be better explained by some other condition or disease. Symptoms of dementia in people cause by HIV often include:
- severe depression
- a lack of interest
- difficulties moving at a normal rate of speed in addition to having early problems with learning and memory.
Prion disease: Prions are abnormal forms of a protein. Developing dementia because of prion disease is very rare. These diseases can be inherited or can happen if a person comes in contact with tissue from a person or an animal that is infected by the prion disease. These diseases include mad cow disease and a disease known as Creutzfeldt-Jakob disease. The dementia occurs suddenly and develops very rapidly. The DSM-5 states that there must be physical evidence that the person has a prion disease for this form of dementia to be diagnosed. The person must also display problems with movement in addition to a very rapid decline in their cognitive features.
Parkinson's disease: Parkinson's disease happens when the areas in a person's brain that produces the chemical dopamine begins to die. Parkinson's disease most often includes problems with moving and with being able to think at a normal rate of speed (the flow of thoughts happens very slowly). According to the DSM-5, about 75% of people with Parkinson's disease will develop a minor or major neurocognitive disorder as well. Most often the problems with dementia that occur in Parkinson's disease are problems with forgetting things (but unlike Alzheimer's disease using reminders can help them remember), language, and with the ability to think in abstract terms.
Huntington's disease: Huntington's disease happens because of heredity. When people inherent the gene for Huntington's disease from one parent, they have a 50% chance of getting the disease. The symptoms usually begin in a person's 40s or 50s. The disease results in uncontrollable movements of the body and is always fatal. The dementia associated with Huntington's disease develops rapidly. The DSM-5 states that the development of dementia in Huntington's disease is unavoidable once the person begins to display the symptoms of the disease.
Other medical conditions: The DSM - 5 lists other categories of medical conditions that can cause neurocognitive disorders. The neurocognitive disorder that happens from these diseases/conditions may or may not be progressive. These categories include:
- Unspecified neurocognitive disorders where the cause of the neurocognitive disorder is not known.
- Neurocognitive disorder due to multiple etiologies where the cause is due more than one different medical condition or other conditions.
- Neurocognitive disorder due to another medical condition that can include other medical conditions not listed above. This could include multiple sclerosis, nutritional problems (for example, a lack of vitamins), normal pressure hydrocephalus (increased pressure because of the fluid in the brain building up), and many other medical conditions. These conditions may be reversible. For example, dementia because of nutritional problems or normal pressure hydrocephalus can often be reversed once the condition is corrected.
Forms of dementia that may not be progressive that are listed in the DSM-5 include:
Traumatic brain injury: When a person suffers a brain injury, they can develop a form of dementia. This injury can happen from:
- having their head strike an object
- being hit with an object
- a result of an acceleration and then a quick stop where the brain moves in the skull
- a result of some other physical force the person can develop a form of dementia.
Dementia from a traumatic brain injury may or may not be progressive. The types of problems that the person will experience from a traumatic brain injury depend on the location of the injury and/or how severe the impact on the brain was. Chronic traumatic encephalopathy (CTE) is a form of traumatic brain injury that happens from experiencing many concussions over time such as in football or boxing.
The DSM-5 lists the symptoms of neurocognitive disorder due to traumatic brain injury as include having one or more of the following:
- A loss of consciousness (being knocked out even for a brief period).
- Problems with orientation (knowing the date, time, location where one is) and with being confused.
- Physical signs of a brain injury from neuroimaging studies (brain scans) or from a physical examination of the person that suggests that there was a brain injury.
Substance/medication use: A person can also develop a neurocognitive disorder because of the use of a medication, illicit drug, or even an overdose on the drug or medication. According to the DSM-5 the neurocognitive disorder must be:
- associated with the use of a drug or medication that can produce cognitive impairment
- happen within the known timeframe associated with the development of cognitive problems
- associated with either using the drug or having stopped using the drug
- cannot be better explained by some other cause.
The types of cognitive problems that happen because of drug use or an overdose can depend on the specific drug and how the drug works. Often the effects of the use of the drug can be reversed once the drug is out of one's system. However, the neurocognitive effects of overdoses may or may not be reversible.