Frontotemporal dementia (FTD) is a progressive untreatable condition. It causes the frontal and temporal lobes of the brain to shrink and it manifests as a behavioural disorder or with speech difficulties. I was unaware of any mimics of FTD (differential diagnoses) that were not equally untreatable.
I was therefore surprised by this article in Neurology which reported 8 patients with the frontotemporal brain sagging syndrome. In this condition, FBSS, there is leakage of cerebrospinal fluid (CSF) which results in low pressure in the brain (intracranial hypotension). The result is that the brain, well, sags.
It i typically the back of the brain that sags in intracranial hypotension, and this leads to distortion of the brainstem. In FBSS however there is in addition, somehow, a reduction in the metabolic activity of the frontal lobe of the brain. It is this frontal hypometabolism that produces the clinical picture that mimics frontotemporal dementia.
There is an added twist to the story as reported, again in Neurology, of a patient whose syndrome spontaneously resolved when he accidentally fell and hit his chest on a chair. The authors said ‘…the fall may have caused a contusion injury and given him an auto-blood patch‘. In plain English, his injury caused a bleed which clotted and (again somehow), sealed the site of cerebrospinal fluid leakage.
Surely a not-to-miss differential next time you are about to diagnose frontotemporal dementia. A reversible dementia!
