The Role of MRI Lesions in Identifying Secondary Progressive Multiple Sclerosis: A Comprehensive Review.

Secondary Progressive Multiple Sclerosis (SPMS) represents a challenging phase of multiple sclerosis, marked by gradual neurological decline and reduced inflammatory activity. In recent years, magnetic resonance imaging (MRI) has become essential for characterizing the neurodegenerative changes underlying SPMS, including white and gray matter damage, brain atrophy, slowly expanding lesions, and iron rim lesions. This narrative review aims to synthesize the current knowledge on established and emerging MRI biomarkers relevant to SPMS, with a particular focus on their diagnostic, prognostic, and therapeutic implications. This review discusses key themes, such as the shift from inflammatory to neurodegenerative mechanisms, the role of advanced imaging techniques, and the limitations of conventional MRI in detecting smoldering disease. In doing so, it identifies current gaps in evidence, including the need for standardized imaging protocols and large-scale longitudinal studies. A clearer understanding and application of MRI biomarkers may facilitate earlier diagnosis, more tailored treatment strategies, and improved outcomes in patients with SPMS.