Memory impairment differs in frontotemporal dementia and Alzheimer's disease

The aim of this study was to assess short-term and long-term explicit memor y and implicit memory in frontotemporal dementia (FTD; frontal variant) and to compare FTD and Alzheimer's disease (AD) patients with similar severity of dementia. Fifteen FTD patients [mean age: 68 years; Mini-Mental State ( MMS): 24], 30 probable AD patients (mean age: 72 years; MMS: 23) and 12 hea lthy subjects participated in the study. The three groups were comparable i n terms of gender and educational level. Short-term memory was assessed wit h the digit span and Corsi block-tapping tests. Explicit verbal memory was assessed with the Grober and Buschke test, and implicit memory with a verba l priming task and a fragmented picture test. FTD patients demonstrated a g enuine memory deficit with impaired digit span, encoding deficit and retrie val strategy difficulties, but preserved implicit verbal and visual priming . Memory patterns differed in AD and FTD: short-term memory and free recall were similarly decreased in FTD and AD but cues provided more benefit to F TD than to AD; encoding was more impaired and the forgetting rate was faste r in AD than in FTD; priming was lower in AD than in FTD. AD patients with clinical and imaging frontal lobe dysfunction tended to have lower memory p erformance and to differ even more from FTD patients than AD patients witho ut frontal lobe dysfunction.