Population included few women
“Our study differs from previous studies on the prodromal phase of MS because these have used indirect markers of this phase, which included unspecific symptoms or disturbances occurring before the clinical onset, compared with a marker of neurodegeneration,” wrote Dr. Bjornevik and colleagues. Initiation of treatment with disease-modifying therapy is associated with reductions in serum NfL levels, and this association could explain why some patients in the current study had higher NfL levels before MS onset than afterward. Furthermore, serum NfL levels are highly associated with levels of NfL in cerebrospinal fluid. “Thus, our findings of a presymptomatic increase in serum NfL not only suggest the presence of a prodromal phase in MS, but also that this phase is associated with neurodegeneration,” wrote the investigators.
The study’s well-defined population helped to minimize selection bias, and the blinded, randomized method of analyzing the serum samples eliminated artifactual differences in serum NfL concentrations. But the small sample size precluded analyses that could have influenced clinical practice, wrote Dr. Bjornevik and colleagues. For example, the researchers could not evaluate distinct cutoffs in serum NfL level that could mark the beginning of the prodromal phase of MS. Nor could they determine whether presymptomatic serum NfL levels varied with age at clinical onset, sex, or race. The small number of women in the sample was another limitation of the study.
The Swiss National Research Foundation and the National Institute of Neurologic Disorders and Stroke funded the study. Several of the investigators received fees from various drug companies that were unrelated to the study, and one researcher received grants from the National Institutes of Health during the study.
SOURCE: Bjornevik K et al. JAMA Neurol. 2020;77(1):58-64.