Pick disease, a type of frontotemporal dementia, can cause on brain imaging due to decreased brain tissue.
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A 65-year-old man comes to the urgent care clinic with his wife who describes dramatic changes in the personality of her husband over the past two years. Specifically, she mentions that he has become increasingly aggressive, hypersexual, and easily agitated. As part of the initial workup, a non-contrast head CT is ordered which shows focal, severe atrophy most predominantly affecting the frontal and temporal lobes. The clinical and imaging findings most likely represent which of the following diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
Pick disease, or Pick's disease, was named after the Czech psychiatrist Arnold Pick, and refers to a degeneration of the frontal and temporal lobes of the brain.
Now, if we step back and take a look at the brain - it can be divided into four lobes: the frontal, temporal, parietal, and occipital lobes.
Within each lobe is a dense network of neurons which allows neurons to communicate with one another.
Like most cells, neurons have a cytoskeleton made up of filaments and microtubules that give the cell its structure.
Microtubules help neurons move molecules along the length of the cell, a bit like a railway track.
And just like in a railway track, the individual units of a microtubule, called tubulins are tied together with a protein called tau.
Tau comes in six different shapes and sizes, or isoforms, and one of the key features of these isoforms is how many times a particular sequence of 29 amino acids gets repeated.
For three of those isoforms, it's repeated three times -- they're called the 3R isoforms -- and for the other three, it's repeated four times -- they're called the 4R isoforms.
Although it's not completely understood why, in Pick disease, 3R isoforms of the tau protein get hyperphosphorylated, meaning that phosphate groups keep binding onto the proteins until no more will fit.
These hyperphosphorylated tau proteins change shape and stop being able to tie together the tubulins in the neuron's cytoskeleton.
What's more, the hyperphosphorylated tau proteins start clumping together, forming tangles of tau protein.
A key difference is that the tangles in Pick disease, are called Pick bodies, and they’re only made up of the 3R tau isoforms, whereas the tangles in Alzheimer's disease, are called neurofibrillary tangles, are they’re made up of both 3R and 4R tau isoforms.
Now, just like in Alzheimer's, neurons with loads of tangled up tau proteins and non-functioning microtubules don't function well, and the neurons get damaged, or undergo apoptosis, which is programmed cell death.