The Difference Between Mild Cognitive Impairment and Alzheimer’s Disease

Washington DC

 As I’ve written before (here, here, and other places), diagnosing Alzheimer’s disease gets complicated and causes significant confusion.  I’m now stuck in the middle of that confusion.  My primary neurologist diagnosed mild cognitive impairment (MCI) that would almost certainly progress to Alzheimer’s.  But what does this “almost certainly” mean?  When I pressed one of my research doctors, on the other hand, he assured me that I had Alzheimer’s.  

How does a doctor make the diagnosis?  A definitive diagnosis can only be made after autopsy of the brain.  In clinical practice, however, the criteria for diagnosis of Alzheimer’s are impairment in memory and impairment in one of six other areas of cognition[1], but the impairment has to be severe enough to be dementia, which means they must interfere with normal activities of daily living.  So since my symptoms don’t yet interfere with day-to-day life, my diagnosis is not Alzheimer’s but “only” MCI. 

But this creates a problem.  Alzheimer’s is a progressive disease that begins as long as thirty years before symptoms develop.  Autopsies of people with either MCI or Alzheimer’s will show the same pathology.  In fact, a person can be cognitively normal and still have the pathological changes found in Alzheimer’s.  So the disease—whatever you call it—has symptoms along a wide continuum, and it doesn’t make sense to name it Alzheimer’s only when it reaches a certain severity.  The medical community, of course, recognizes this problem and is moving toward a new definition based on a whole new set of criteria of specific physical changes in the brain that eventually develop into Alzheimer’s dementia.  Those criteria will include even those who are years from any impairment.  So people will be classified as “preclinical Alzheimer’s,” or “mild Alzheimer’s,” or “Alzheimer’s dementia.”

But that definition won’t be useful in practice until there are reliable tests, such as brain scans or spinal fluid analysis, that reliably detects and measures those physical changes in the brain.  And, so far, the tests haven’t been proved to be reliable. 

 We’re still stuck with the problem that you don’t have Alzheimer’s until you have developed dementia, that is, until your symptoms interfere with your daily life. 

Why should I care? 

The statistics for how large a problem Alzheimer’s is count only those with dementia, which means that they grossly underestimate the numbers affected with the disease, unless the reader understands it all.  There are probably twice as many people with some degree of cognitive impairment from Alzheimer’s than is usually reported.  And that’s misleading.

The current definition also makes it difficult for those with early symptoms to know what’s going on.  If somebody is told that he “only” has MCI, will he be falsely comforted?  Do I, for instance, have Alzheimer’s or don’t I?  Using the current criteria, I don’t.  Using the more inclusive criteria, I probably do.  What do I tell others?  The subtitle of this blog is: “A Memoir from Inside Alzheimer's Disease.”  Is that misleading?  Or should I go through the whole spiel every time I give a talk or lead a discussion?  And if I did, wouldn’t that confuse people even more?

Can MCI sometimes be a separate diagnosis?  It’s unclear.  Certainly the vast majority of time, MCI develops into Alzheimer’s or one of the other known dementias.  But, for instance, the Mayo Clinic writes that “some people with mild cognitive impairment never get worse, and a few eventually get better.”  But that doesn’t make sense unless MCI is a separate, non-progressive disease, and I can’t find scientist suggesting that.

As Alzheimer’s loses its stigma, more patients with MCI will present themselves to medical people, renewing interest in the questions around MCI.  Let’s hope that that murkiness around mild cognitive impairment will clear up soon.

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[1] In addition to dementia, the diagnosis of Alzheimer’s requires an impairment in memory and at least one other cognitive deficit:

• aphasia (abnormal speech), 
• executive function impairment (difficulty with planning, judgment, mental flexibility, abstraction, problem-solving, etc),
• agnosia (impaired  recognition of people or  objects), or
• apraxia (impaired performance of  learned motor skills).