Cognitive Function and Health‐Related Quality of Life in Patients With Multiple Sclerosis: Clinical Evidence From Japan

ABSTRACT Cognitive impairment is a common symptom of multiple sclerosis (MS) and has a substantial impact on quality of life (QoL). In Japan, cognitive assessment has traditionally lagged behind that in Western countries. With the emerging concept of smoldering‐associated worsening, the importance of longitudinal cognitive monitoring is becoming increasingly recognized. In this review, we aimed to systematically integrate existing evidence on cognitive function, neuroimaging features, clinical symptoms, and QoL in Japanese patients with MS to support improved clinical management. A literature review was conducted using PubMed and the Clinical and Experimental Neuroimmunology database, focusing on studies evaluating cognition and QoL in Japanese patients with MS. Validation studies have confirmed the applicability of Western batteries (Brief Repeatable Battery of Neuropsychological Tests and Brief International Cognitive Assessment for Multiple Sclerosis) to Japanese patients; however, copyright restrictions limit their widespread use. The iPad‐based Symbol Digit Modalities Test has been validated using Japanese‐specific normative data, revealing significant differences from US norms. Neuroimaging studies in Japan have demonstrated that cognitive decline correlates with cortical lesions, gray matter atrophy, and regional volume loss. Cognitive dysfunction is also associated with olfactory impairment, driving performance, and Theory of Mind. Notably, cognitive processing speed is a significant predictor of health‐related QoL and employment status, independent of physical disability. Objective cognitive assessment is feasible and essential in Japanese clinical practice. Integrating validated digital tools with an improved understanding of the links between cognition, brain pathology, and daily functioning may improve the management of patients with MS in Japan.