The Basis of Cognitive and Behavioral Dysfunction in Amyotrophic Lateral Sclerosis.

OBJECTIVE: To summarize and evaluate evidence pertaining to the clinical, genetic, histopathological, and neuroimaging correlates of cognitive and behavioral dysfunction in amyotrophic lateral sclerosis (ALS). METHODOLOGY: We comprehensively reviewed the literature on cognitive and behavioral manifestations of ALS, narrating findings from both cross-sectional and longitudinal studies. We discussed knowledge gaps in the evidence base and key limitations affecting studies to date, before formulating a framework for future research paradigms aimed at investigating clinicopathological correlates of neuropsychological dysfunction in ALS. RESULTS: Studies have demonstrated clinical associations with cognitive dysfunction in ALS e.g., bulbar-onset of symptoms, pathological associations (extramotor TDP-43 deposition), and imaging associations (frontotemporal involvement). The most common behavioral deficit, apathy, is highly associated with verbal fluency, but longitudinal studies assessing behavioral dysfunction in ALS are comparatively lacking. CONCLUSION: Longitudinal studies have been helpful in identifying several potential correlates of cognitive and behavioral dysfunction but have frequently been confounded by selection bias and inappropriate testing platforms. This review provides a framework for more robust assessment of clinicopathological associations of neuropsychological abnormalities in ALS in the future, advocating for greater utilization of pre-symptomatic C9orf72 repeat expansion-carrying cohorts.