Is hippocampal volume a good marker to differentiate Alzheimer's disease from frontotemporal dementia?

BACKGROUND: Previous studies analyzed the ability of hippocampal volumes (HV) to differentiate Alzheimer's disease (AD) from frontotemporal dementia (FTD). However, these studies did not include patients selected according to clinico-biological criteria, using pathophysiological biomarkers.
OBJECTIVE: To analyze the effectiveness of hippocampal volumetric measures to distinguish AD from behavioral variant FTD (bvFTD), using strict inclusion criteria based on clinical and pathophysiological markers.
METHODS: Seventy-two participants were included: 31 AD patients with predominant and progressive episodic memory deficits associated with typical AD cerebrospinal fluid (CSF) profile and/or positive amyloid imaging (PET with 11C-labeled Pittsburgh Compound B [PiB]), 26 bvFTD patients diagnosed according to consensual clinical criteria and with no AD CSF profile, and 15 healthy controls without amyloid retention on PiB-PET exam. HV were segmented with an automated method and were normalized to total intracranial volume (nHV).
RESULTS: Significant reductions in HV were found in both AD and bvFTD patients compared with controls, but there were no significant difference between AD and bvFTD patients. Mean nHV distinguished normal controls from either AD or bvFTD with high sensitivity (80.6% and 76.9%, respectively) and specificity (93.3% for both), but it was inefficient in differentiating AD from bvFTD (9.7% specificity). There was no difference in the clinical and neuropsychological profiles according to HV in bvFTD and AD patients.
CONCLUSIONS: When considered alone, measures of HV are not good markers to differentiate AD from bvFTD. Hippocampal sclerosis associated with FTD may explain the high degree of overlap in nHV between both groups.