The Faces of “Too Late”—A Surprisingly Progressive Cohort of “Stable” Relapsing Remitting Multiple Sclerosis Patients

<i>Background and Objectives</i>: Although available therapies have changed the natural evolution of multiple sclerosis (MS), in time some patients assume a progressive course and no longer respond to treatment. There is no definitive clinical or laboratory parameter to certify MS progression from relapsing remitting MS (RRMS) to secondary progressive MS (SPMS) in early phases of transition. Our study aims to evaluate the value of clinical parameters and serum neurofilament light chain levels (sNfLs) as early warning signs of conversion to SPMS. <i>Materials and Methods</i>: The Expanded Disability Status Scale (EDSS), Nine-Hole Peg Test (9HPT), 25-foot walk test (25FWT) and Symbol Digit Modalities Test (SDMT) were evaluated at 12 months apart in a cohort of 83 RRMS treated patients. sNfLs were evaluated at the second time point. <i>Results:</i> sNfLs correlate with EDSS and SDMT, with EDSS change and disease duration. Clinical parameters correlate among themselves and perform well in supporting the diagnosis of SPMS in logistic regression and ROC curves analysis. Eighty percent of the RRMS patients in our study (of which 65% are treated with high-efficacy disease-modifying drugs) showed some type of progression independent of relapses (PIRA) after 12 months, with one in five patients experiencing isolated cognitive worsening and almost two-thirds some type of motor worsening. We found no differences in terms of progression between patients treated with platform drugs versus high-efficacy drugs. <i>Conclusions</i>: An elevated level of progression independent of relapses (PIRA) was found in our cohort, with high-efficacy drugs providing no supplementary protection. As sNfL levels were correlated with the progression of EDSS (the main clinical progression marker), they may be considered potential prognostic markers, but further studies are necessary to precisely define their role in this direction. The lack of early sensitive markers for risk of progression may contribute to therapeutic delay and failure.