Abstract
BackgroundRecent work suggests that ALS and frontotemporal dementia can occur together and share at least in part the same underlying pathophysiology. However, it is unclear at present whether memory deficits in ALS stem from a temporal lobe dysfunction, or are rather driven by frontal executive dysfunction. In this study we sought to investigate the nature of memory deficits by analyzing the neuropsychological performance of 40 ALS patients in comparison to 39 amnestic mild cognitive impairment (aMCI) patients and 40 healthy controls (HC). The neuropsychological battery tested for impairment in executive functions, as well as memory and visuo-spatial skills, the results of which were compared across study groups. In addition, we calculated composite scores for memory (learning, recall, recognition) and executive functions (verbal fluency, cognitive flexibility, working memory). We hypothesized that the nature of memory impairment in ALS will be different from those exhibited by aMCI patients.ResultsPatient groups exhibited significant differences in their type of memory deficit, with the ALS group showing impairment only in recognition, whereas aMCI patients showed short and delayed recall performance deficits as well as reduced short-term capacity. Regression analysis revealed a significant impact of executive function on memory performance exclusively for the ALS group, accounting for one fifth of their memory performance. Interestingly, merging all sub scores into a single memory and an executive function score obscured these differences.ConclusionThe presented results indicate that the interpretation of neuropsychological scores needs to take the distinct cognitive profiles in ALS and aMCI into consideration. Importantly, the observed memory deficits in ALS were distinctly different from those observed in aMCI and can be explained only to some extent in the context of comorbid (coexisting) executive dysfunction. These findings highlight the qualitative differences in temporal lobe dysfunction between ALS and aMCI patients, and support temporal lobe dysfunction as a mechanism underlying the distinct cognitive impairments observed in ALS.
Highlights
Recent work suggests that Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia can occur together and share at least in part the same underlying pathophysiology
It is wellestablished that ALS shares clinical [1], pathological [2] and genetic [3] characteristics with frontotemporal dementia (FTD), and this overlap has led some studies to assert the existence of a single continuum on which both ALS and FTD lie [4,5]
Patients with ALS (13.0 ± 2.5) have less educational years than amnestic mild cognitive impairment (aMCI) (14.6 ± 2.8), but both patient groups did not differ from healthy controls (14.0 ± 2.1)
Summary
Recent work suggests that ALS and frontotemporal dementia can occur together and share at least in part the same underlying pathophysiology It is unclear at present whether memory deficits in ALS stem from a temporal lobe dysfunction, or are rather driven by frontal executive dysfunction. In this study we sought to investigate the nature of memory deficits by analyzing the neuropsychological performance of 40 ALS patients in comparison to amnestic mild cognitive impairment (aMCI) patients and healthy controls (HC). The temporal lobe pathology as hippocampal atrophy is a hallmark in aMCI but it occurs to a much smaller extent than in AD [39] This group of patients is comparable to patients with ALS in terms of hippocampal degeneration. In the current work we focussed on verbal memory performance and hypothesized a qualitative difference between patients with ALS and aMCI
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