This has become a highly fashionable opinion to parrot and it threatens to send us back to the old days where we didn't pay any attention to cognitive decline at all, sometimes with disastrous results. It's based on the seemingly sensible notion that an early diagnosis of MCI (secondary to Alzheimer's disease which typically means an amnestic type of MCI rather than MCI NOS) only favorably impacts outcome if you have a disease modifying treatment for the underlying condition. While that certainly sounds like a reasonable assumption – as we have no disease modifying treatment – it misses a huge and critical point, namely that patients with prodromal or early stage Alzheimer's disease need more hands-on care and most especially need to be protected from the multitude of delirogenic influences in our medical system, even if standard cholinergic and NMDA antagonist therapy is not truly disease modifying.
Evidence is now overwhelming that delirium is not orthogonal to the rate of decline in Alzheimer's disease, and that it acts as a serious accelerant, roughly (on average) doubling the rate of decline from the point of induction of the first delirium (and possibly even being part of what transitions patients from preclinical stages into clinical stages of Alzheimer's disease). Delirogenic influences include the widespread and frankly at times naïve use of centrally acting anticholinergic medicines in the elderly, oftentimes without any regards for whether they might be in cognitive decline, commonplace bacterial infections (with urinary tract infections being the single most common etiology for confusional states), other CNS depressant medicines particularly benzodiazepines and opiates which are potently delirogenic, and of course other severe metabolic, endocrine or infectious conditions, and lastly, concussion and head trauma, a common comorbidity to falls which the elderly are disproportionately exposed to. While obviously some of these things cannot be prevented, vigilance about iatrogenesis of delirium is unacceptably low in our healthcare system in my judgment. The preventable and regrettable induction of delirium in a patient with Alzheimer's disease that could have been avoided with more sophistication and awareness of the disease and its comorbidities literally robs them of potential time in the community and in their home environment until they become totally disabled by the disease and then require 24-hour daycare.
In this sense unfortunately, and the irony of this is not widely appreciated, we're far better at accelerating Alzheimer's disease than we are at slowing it down. Additional nontrivial accelerants may include commonplace vitamin B12 and vitamin D deficiencies which should be identified and corrected anyway in primary care, but where the diagnosis of MCI presumed secondary to early AD should increase vigilance about these issues as well. In these critically important senses, I think this highly fashionable opinion (presented as factual as opposed to it being simply an opinion) is just plain wrong.