Alzheimer’s disease is the most common type of major neurocognitive disorder, formerly known as dementia. Learn more about the difference between major neurocognitive disorder, mild neurocognitive disorder, and the pre-symptomatic phase of Alzheimer’s disease.
Bill looked at his father, Walter, who for the third time was telling us about the great times he had in the army after he enlisted around 1950. Walter became a successful engineer who worked productively into his mid-70s. When he experienced increasing forgetfulness, he recognized the need to wind down his career. He moved into the friendly and stimulating environment of a local assisted living facility’s memory unit. His life there was a good one. His close family relationships continued. He enjoyed detailed memories of the past, but recent events no longer made a lasting impression on his mind. Bill asked me, “What is my father’s diagnosis? Is he demented? Does he have Alzheimer’s disease? And what’s the difference between dementia and Alzheimer’s disease?”
Everything Changed in 2013
This question often comes up in a clinical interview, and up until recently the answer would have been that dementia is diagnosed when a person has a severe memory problem in addition to difficulty with language or another cognitive function, and that Alzheimer’s disease is the most common type of dementia. In 2013, though, everything changed.
The new psychiatric Diagnostic and Statistical Manual (DSM 5) renamed “dementia” as “major meurocognitive disorder” and added a new, less severe category of cognitive difficulty called mild neurocognitive disorder.
Major neurocognitive disorder is diagnosed when disturbance of a single cognitive ability is severe enough to interfere with independence and the disturbance is not caused by drug use, delirium, or various other medical or psychiatric conditions. The cognitive abilities that are tested for this diagnosis are:
- complex attention
- language (expression and comprehension)
- executive function (skills that, for example, enable people to plan, organize, remember things, prioritize, or pay attention to tasks)
- perceptual-motor function (the visual perception of spatial relationships among objects)
- learning and memory, and
- social cognition.
Where Does Alzheimer's Fit In?
Alzheimer’s disease is the most common type of major neurocognitive disorder, but it is only one of many possible causes. Vascular cognitive impairment, dementia with Lewy bodies, frontotemporal dementia, Parkinson’s disease, Huntington’s disease, HIV, traumatic brain injury, and other conditions each can cause severe cognitive changes.
Mild neurocognitive disorder (formerly called mild cognitive impairment or MCI), by contrast, is diagnosed when a less severe cognitive problem exists, manifested as difficulty with one of the six listed mental functions (listed above) that is significant enough to require compensatory activities, such as writing everything down in order to remember. Mild neurocognitive disorder, by definition, is not bad enough to rob a person of basic independence. The DSM 5 says that one possible cause of mild neurocognitive disorder is Alzheimer’s disease, but it is only one of many medical or psychiatric conditions that can cause this clinical condition. In other words, Alzheimer’s disease can be present without major neurocognitive disorder or dementia, and dementia can be present without Alzheimer’s disease.
Alzheimer’s Begins Years before Symptoms are Apparent
The DSM 5’s new definitions followed a series of very influential articles published by Alzheimer’s disease researchers in 2011. These experts encouraged us to recognize Alzheimer’s disease as a disease pathology rather than as a clinical syndrome. In other words, to understand that the effects of Alzheimer’s disease on the brain begin many years before memory loss or behavioral changes become apparent. The 2011 expert statement defined three stages of Alzheimer’s disease. The dementia (major neurocognitive disorder) phase is only the final stage. Earlier symptoms are recognizable in a symptomatic, pre-dementia phase (mild neurocognitive disorder). With amyloid PET scanning or various other biomarker measurements, doctors can also determine the presence of Alzheimer’s disease pathology in the brains of people with no apparent clinical symptoms. This is the asymptomatic, or pre-symptomatic phase of Alzheimer’s disease.
The illustration below shows that Alzheimer’s disease can manifest itself with clinical symptoms ranging from none to major. Alzheimer's, however, is not the only cause of major neurocognitive or mild neurocognitive disorders.
A Diagnosis and an Important Question
When Walter was examined further in our clinic, we decided that his memory troubles were indeed the result of Alzheimer’s disease. He had major neurocognitive disorder and we were unable to identify any other medical or psychiatric disorder that could be responsible for his condition. An amyloid PET scan of Walter’s brain would likely have showed accumulation of beta amyloid, the disease-associated protein found in the brains of people with Alzheimer’s. Bill asked, “What about me? Will I get Alzheimer’s disease?”
What we know now from biomarker research allows us to answer Bill’s question in a way that would not have been possible for past generations. We can tell Bill that he definitely does not have dementia, and that if he has Alzheimer’s disease it is in the pre-symptomatic stage. Occurrence of the disease in his father puts Bill at a small increased risk, so we’ll watch him in the future. For the present, we’ll encourage him to adopt a brain-healthy lifestyle that includes management of chronic medical diseases, stress reduction, healthy eating habits, adequate sleep, plenty of physical activity, engagement with others, and cognitive stimulation. Of course, this brain healthy lifestyle is a good prescription for all of us!
This content was last updated on: October 10, 2017
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