Cognitive impairment is a debilitating symptom experienced by approximately 50% of patients with multiple sclerosis (MS). Claire Riley, MD, Columbia University Irving Medical Center, New York, NY, discusses a subset of MS in which cognition is primarily affected. Dr Riley highlights the importance of recognizing and accessing cognitive changes in MS, including early in the disease course. Throughout the course of the disease and as the MS population ages, some other factors can intensify or stimulate cognitive deficits. Dr Riley goes on to discuss research conducted by her group evaluating the relationships between Symbol Digit Modalities Test (SDMT) performance and T2 lesion volume on magnetic resonance imaging (MRI). This interview took place during the ACTRIMS Forum 2021.