Pregnancy in MS typically goes along with reduced disease activity in the third trimester, followed by an increase in relapse frequency postpartum. Neurofilament light chain levels in serum (NfL) is a specific biomarker of neuroaxonal injury. Increased NfL levels are associated with relapses and MRI activity, while disease modifying treatment (DMT) response is reflected by a decrease of NfL.
The objective of this study was to evaluate whether interrupting DMT due to pregnancy leads to increased NfL levels in MS.
We investigated prospectively documented pregnancies in the Swiss MS Cohort Study. Serum samples were collected 6- or 12-monthly and were analyzed by Simoa NF-light® assay. Uni- and multivariable mixed effect models were used to investigate associations between clinical characteristics and longitudinal NfL levels.
We investigated 72 pregnancies in 63 relapsing MS patients (median age 31.4; disease duration 7.1 years; EDSS 1.5 at last visit before birth). In total, 433 samples were included: 92 during pregnancy or up to initiation of DMT but max. 9 months postpartum (pregnancy/post-partum period, pp), 167 prior to pp and 174 after the pp. Four patients had no DMT before, during and after pregnancy. DMT was continued in 13/72 pregnancies (>6 months during pregnancy: 6 rituximab/ocrelizumab, 4 natalizumab, 1 interferon-beta 1a i.m., 1 fingolimod and 1 glatiramer acetate). In univariable analysis, NfL levels were on average 22% higher during vs. outside the pp (β: 1.22, 95%CI: 1.10-1.35; p<0.001). We observed 29 relapses during the pp. In a multivariable analysis, relapses (within 120 days before serum sampling) were associated with 98% higher NfL (β: 1.98, 95%CI: 1.75-2.25; p<0.001); NfL was 7% higher per EDSS step increase (β: 1.07, 95%CI: 1.01-1.12; p=0.013) and on average 13% higher during vs. outside the pp (β: 1.13, 95%CI: 1.03-1.24; p=0.009). The effect of the pp on NfL disappeared after including DMT exposure (yes/no) at the sampling timepoint to the model (β:1.07, 95%CI: 0.97-1.18; p=0.178). Patients sampled during DMT had on average 12% lower NfL levels compared to patients without (β:0.88, 95%CI: 0.79-0.98; p=0.019).
Higher NfL levels were found during pp. This increase was independent of relapses suggesting increased subclinical disease activity during this time span. After including DMT into the model the effect of pregnancy on NfL disappeared: strategies allowing to continue DMT during pregnancy may be warranted.