Serum Neurofilament Levels and PML Risk in Patients With Multiple Sclerosis Treated With Natalizumab

Abstract

Objectives: The study aimed to assess the potential for serum neurofilament light chain (NFL) levels to predict the risk of progressive multifocal leukoencephalopathy (PML) in natalizumab (NTZ)-treated patients with multiple sclerosis (MS) and to discriminate PML from MS relapses.

Methods: NFL levels were measured with single molecule array (Simoa) in 4 cohorts: (1) a prospective cohort of patients with MS who developed PML under NTZ therapy (pre-PML) and non-PML NTZ-treated patients (NTZ-ctr); (2) a cohort of patients whose blood was collected during PML; (3) an independent cohort of non-PML NTZ-treated patients with serum NFL determinations at 2 years (replication cohort); and (4) a cohort of patients whose blood was collected during exacerbations.

Results: Serum NFL levels were significantly increased after 2 years of NTZ treatment in pre-PML patients compared with NTZ-ctr. The prognostic performance of serum NFL levels to predict PML development at 2 years was similar in the NTZ-ctr group and replication cohort. Serum NFL levels also distinguished PML from MS relapses and were 8-fold higher during PML compared with relapses.

Conclusions: These results support the use of serum NFL levels in clinical practice to identify patients with relapsing-remitting MS at higher PML risk and to differentiate PML from clinical relapses in NTZ-treated patients.

Classification of evidence: This study provides Class I evidence that serum NFL levels can identify NTZ-treated patients with MS who will develop PML with a sensitivity of 67% and specificity of 80%.

Figure 1. Increased NFL Levels in Serum After 2 Years of NTZ Treatment in Pre-PML Patients Compared With NTZ-ctr

Graphs comparing serum NFL levels between pre-PML and NTZ-ctr patients at baseline (T0; n = 16 for pre-PML and n = 36 for NTZ-ctr), after 1 (T1; n = 12 for pre-PML and n = 36 for NTZ-ctr) and 2 years (T2; n = 12 for pre-PML and n = 34 for NTZ-ctr) of treatment and during PML (n = 13). Each symbol represents an individual, and horizontal bars indicate the median values and interquartile ranges. A y-axis segmentation was performed to represent better high and low serum NFL levels. *Refers to p values <0.05. **Refers to p values <0.01. ***Refers to p values <0.001 in Mann-Whitney U tests (unpaired data) and Wilcoxon matched-paired test (paired data). NFL = neurofilament light chain; NTZ = natalizumab; PML = progressive multifocal leukoencephalopathy.

Figure 2. Serum NFL Levels Differentiate Between Pre-PML and NTZ-ctr Patients After 2 Years of NTZ Treatment

(A) Performance of serum NFL levels to discriminate between pre-PML and NTZ-ctr patients after 2 years of treatment. (B) Distribution of serum NFL levels in the NTZ-ctr cohort at 2 years of treatment (n = 34), and in an independent cohort of patients with MS treated with NTZ for 2 years (replication cohort; n = 29). (C) Performance of the serum NFL levels to discriminate between pre-PML patients at 2 years and patients from the replication cohort after 2 years of treatment. NFL = neurofilament light chain; NTZ = natalizumab; PML = progressive multifocal leukoencephalopathy.

Figure 3. NFL Levels in Serum Identify PML From MS Relapses

(A) Distribution of serum NFL levels in the relapsing cohort (n = 30) and during PML (n = 13). A y-axis segmentation was performed to represent better high and low serum NFL levels. *p = 3 × 10⁻⁶ In the relapsing cohort: untreated patients are represented in solid squares and interferon-beta–treated patients in solid triangles. (B) Performance of the serum NFL levels to discriminate between MS relapses and PML. Numbers in parentheses represent 95% CIs of the AUC. AUC = area under the ROC curve; MS = multiple sclerosis; NFL = neurofilament light chain; PML = progressive multifocal leukoencephalopathy; Se = sensitivity; Sp = specificity.