The most common disease which causes dementia in older age is Alzheimer disease (AD). More than half of all cases of dementia result from AD.

Dementia in AD results from a gradual accumulation of metabolic by-products in the brain that are not cleared out well or fast enough, and brain cells eventually malfunction and die. There are more technical descriptions, but this captures the gist. This video offers a helpful explanation. 

The memory centers of the brain are most susceptible to damage in AD. Other forms of progressive dementia, such as Lewy Body disease, impact other parts of the brain early on. Memory loss is most always the first sign of AD dementia. Most progressive neurodegenerative conditions impact much or all of the brain over time (and if the afflicted person lives long enough).

Much of my clinical work, today, involves interviewing patients about their histories, reviewing their records, and administering advanced tests of memory and thinking skills. Some minor changes in mental function can be attributed to aging, alone, and possibly other conditions (e.g., head injury). More serious and worsening changes are usually attributed to a disease process or processes. Sometimes personal health behaviors impact progression too. Alcohol consumption in dementia is rarely a good thing, for example.

I consider how each individual may have changed from their own personal baseline - whatever I can know or surmise of it - and also relative to published norms based on age, education level, sex, and other factors. Example: Is this person performing at a level I would expect based on being male, 74, and educated at the BA level?

A common "mental status" screening measure is the Montreal Cognitive Assessment (or "MoCA" for short). Developed as a more sensitive alternative to the Folstein Mini Mental State Exam, the MoCA assesses orientation, language, attention, memory, and problem solving skills in a brief, 30-point test that can be administered in 10 minutes or so. It is a solid test, but has serious limitations, too.

The MoCA has both a "low floor" and a "low ceiling" in testing terms. It tests abilities down to a very low functional level, but it doesn't test skills much past the minimal level necessary for success in daily living. The expectation is that most adults who take the MoCA, regardless of education or occupational attainment, will score 30 of 30 points or close to it. The MoCA is most useful as a screening measure when scores fall below this minimal functional threshold.

This reality gets lost in the media and online forums about neurocognitive testing. A perfect score says little about a person's intellectual level. There's no such thing as "acing" the MoCA, as some might suggest. Scoring at or very close to 30 points simply says that your cognitive capacity meets a minimal standard for success in daily life. That's all!

The MoCA is an entry point to evaluation and usually not a definitive evaluation in itself. A "normal" score indicates you meet a basic level of cognitive function for daily living. Persons can score near 30 points on the MoCA and still have serious cognitive deficits, however. Only advanced neuropsychological testing can tease this out.

Persons with high educational and/or occupational attainment can often do fine on the MoCA despite injuries or disease processes having real impacts on their brains. This occurs in stroke patients with some regularity. A stroke is often focal (i.e., in one area) and may impact only one or a handful of skills. Basic thinking captured by the MoCA may still be intact and so deficits doesn't show up on this test at all. Extra testing is needed.

The MoCA can still be diagnostic on its own in certain circumstances - most often when various lines of evidence converge. For example, a person with a clear family history of dementia and documented functional changes over time (e.g., in family reports) who also scores below 20 points on the MoCA is very likely to have AD or another progressive dementia. Advanced testing may be unnecessary in such cases.

Psychologists and neuropsychologists with specialized training and experience in neurocognitive testing and evaluation administer the advanced tests of memory and thinking to address the full range of cognition from very superior to severely impaired.

We all have cognitive strengths and weaknesses. These are relative to each other in life and influenced by our genetics, upbringing, experiences, environments, and the diseases we may be subject to over time. Measuring and documenting personal patterns of these strengths and weaknesses is essential for understanding what's going on when decline is noticed and any diagnostic implications. 

As a screening test, the MoCA plays a critical early role in the assessment process by addressing what's most often the first question: 

Is this person's cognitive function in the normal range or not? 

When the answer is "not,"  that's when advanced testing - what I do professionally with older adults - is the next step.

A note about my practice... While I like the MoCA and am certified in its use, I often prefer to administer the Saint Louis University Mental Status Exam (SLUMS). The MoCA was developed to apply across all ages, whereas the SLUMS (I hate this acronym) targets older persons and the kinds of deficits which often appear in AD and other progressive dementias. This is a personal preference only and not an endorsement!