Alzheimer’s disease unfolds over the course of decades.  Despite the intensive search, there are no accurate and reliable biological markers for Alzheimer’s disease.  Diagnosis is based on a combination of factors including details of course and history gathered from the person who has memory loss as well as family and/or friends.   There must also be a medical work up searching for treatable causes of memory loss such as thyroid function, status of diabetes, anemia, and imaging studies.  The standard of care also requires cognitive evaluation to map out strengths and weaknesses and stage the disease.  Finally, diagnosis requires clinical judgment.

There is a push for a new set of criteria that diagnoses Alzheimer’s disease into three stages and is based on the fact that Alzheimer’s disease begins well before symptoms emerge (Practical Neurology, 2013, March/April, 34-35)).  The first stage is the preclinical stage.   This is the stage before symptoms and before memory loss appears.   It is founded on finding measurable changes in the brain, cerebrospinal fluid, and/or blood.  These changes occur 20 or more years before symptoms.  The rub is that there are no guidelines on how to make this diagnosis and no biomarkers that are no generally accepted biomarkers for making this diagnosis.  It seems to me that this is like arresting someone before they commit the crime you think they will commit.

Mild cognitive impairment is the second stage.  This stage is mild (the afflicted person can still function in daily life) yet there are measureable changes in memory that are noticeable to family and friends.  The latest estimate is that 10-20% of those over 65 have mild cognitive impairment. There are subtypes of mild cognitive impairment and those forms accompanied by memory loss are the most likely to decline.  Some with mild cognitive impairment decline whereas others do not.  There is no known reason for this difference.  If accurate biomarkers become available, those with mild cognitive impairment and positive markers will be reclassified as mild cognitive impairment due to Alzheimer’s disease.

Dementia due to Alzheimer’s disease is the third and final stage.  Independence is lost as the symptoms interfere with daily life.  This stage is where Alzheimer’s disease is diagnosed currently.

Are these criteria an improvement over what we use now?  The intent is to develop treatments that delay or modify Alzheimer’s disease before it produces symptoms.  But there are no good criteria yet for stage one and biomarkers are still research tools.  Do we really want to tell someone that they have Alzheimer’s disease when they have no symptoms and may not develop any?