Hippocampal sclerosis in tau-negative frontotemporal lobar degeneration

Tau-negative frontotemporal lobar degeneration (FTLD) can be divided into those with motor neuron disease (FTLD-MND), and those without MND, but with ubiquitin-immunoreactive neuronal inclusions (FTLD-U). Some authors group FTLD-U and FTLD-MND together as tau-negative FTLD, but others separate them on the basis of clinical, pathologic and imaging differences. In 103 cases of pathologically confirmed, tau-negative FTLD (FTLD-MND and FTLD-U), we assessed the frequency of hippocampal sclerosis defined as neuronal loss in the subicular or CA1 regions of the hippocampus. The subjects in the FTLD-U group were older at death and had longer disease duration. After adjusting for age at death and disease duration, we found a significant difference in the frequency of hippocampal sclerosis in the FTLD-U group (79%) compared to FTLD-MND group (26%) (p=0.02). The difference in frequency of HpScl in FTLD-U compared to FTLD-MND is further evidence that they are separate clinicopathologic entities.