People are always asking when mild cognitive impairment turns into Alzheimer's disease. I commonly encounter this question in the press, I hear it discussed at conferences, and physicians wrestle with it regularly. Despite the centrality of this question in so many forums of cognitive health, it is a nonsensical inquiry with inherent flaws. Additionally, it propagates confusion that I want to clarify today.
There are many medical conditions that can cause a subtle cognitive deficit. Pondering whether or not mild cognitive impairment will "convert" to Alzheimer's disease obscures the fact that mild cognitive impairment is a symptom of an underlying medical problem, not the problem itself. In fact, some mild cognitive impairment is actually caused by Alzheimer's disease; therefore, the prospect of conversion does not belong in a logical, informed discussion.
The Correct Question
When mild cognitive impairment is present, we should not ask if or when it will convert to Alzheimer's disease. The correct question is: what is the cause of the impairment?
If the answer is Alzheimer's disease, then the folly of a conversion outcome is clear: the disease precedes the impairment and not vice versa. If the mild cognitive impairment is caused by some other medical condition (e.g., depression, vascular disease, thyroid disease, anxiety, etc.) then it is equally futile to consider whether or not it will convert to Alzheimer's disease, as these medical problems are separate and distinct.
All of this is not to say that a person with mild cognitive impairment caused by untreated depression will never get Alzheimer's disease because they may. In fact, some medical conditions that can cause mild cognitive impairment confer a greater risk for Alzheimer's disease. Nonetheless, the notion of "converting" from mild cognitive impairment to Alzheimer's disease is illogical.
We Get it Right With Other Diseases
A good analogy would be to learn of a patient with excessive thirst and blurry vision and then wondering if these symptoms will ever "convert" to diabetes. Most physicians would perform a diagnostic workup, take note of the patient's blood sugar and then either diagnose diabetes or rule it out immediately. There would be no debate about whether or not the symptoms would eventually covert to diabetes.
We must do the same with mild cognitive impairment. That is, physicians should perform a workup on patients and identify the underlying cause of the symptoms so that the patient may benefit from timely, appropriate treatment.
The Need for Clarity
The perpetration of the idea that mild cognitive impairment might or might not convert to Alzheimer's disease causes some (if not many) primary care physicians to take a "wait and see" attitude. In those cases, it prevents them from proactively diagnosing the cause of the mild cognitive impairment and treating it. Giving any credence to the notion that mild cognitive impairment is a sporadically progressive precursor to Alzheimer's disease is a barrier to clarity and interferes with a higher standard of care in this field.
Given that, on average, Alzheimer's disease is diagnosed 8–10 years after the onset of the earliest clinical symptoms, improvements in the timeliness of intervention is our most immediately graspable improvement for care in this field. There is no doubt that misconceptions about mild cognitive impairment that delay early diagnosis cause needless suffering.