Some Clarification on my Hippocampus Volumes

Someone posted a comment recently about how remarkable the changes were in my hippocampus volumes measured between 2017 and 2021.  In Beating the Dementia Monster, we cited research showing that brain volume may increase with exercise.  This might include an increase in volume of the hippocampus, ground zero for memory processing.  So, in 2017 and 2018, my normalized hippocampus volume was recorded in two MRIs as <1 percentile for men my age.  In other words, among 100 men my age, I would have the smallest hippocampus.  The conclusion was that my hippocampus had atrophied due to Alzheimer's disease.  But in 2021, a new MRI found that its volume was in the middle of the normal range, at the 52 percentile.

This was certainly good news.  Hippocampus volumes <1 percentile is what is found with people in memory care.  Nevertheless, the numbers here can be deceiving.  This does not mean that my hippocampus got larger.  The raw data says that it did not.  It does mean that the atrophy of my brain had been dramatically slowed. 

While some research found increased brain volume in some people who began exercising, as a rule, all brains atrophy as we age.  Normal brains atrophy at a rate of about 1% per year, while the brains of Alzheimer's disease patients atrophy at a rate of about 4% per year.  So by tracking hippocampus volume as a percentile for men my age, we are actually measuring the rate at which my hippocampus is atrophying with respect to other men.

My neurologist tells me that the normalization processes uses men in 10-year increments.  For example, if I was in my 60s in 2017, my hippocampus would likely be compared to men in an age range of 60 to 69.  I would have been 68, near the older end of the decade.  So (if my understanding is correct) my brain was being compared with men as much as eight years younger than I was.  But when my MRI was conducted in 2021, I was 72, and my volume was now being compared with men in a range of 70 to 79 years of age.  It shouldn't be surprising that my normalized volumes were better on the 2021 MRI than earlier ones, because I was now being compared to men older than I was.

Make no mistake, <1 percentile is a bad number, and it supports the Alzheimer's diagnosis.  Applying the tools of the Dementia Toolkit has significantly altered the course of my cognitive impairment.