# Case Report: Neurofilament light chain in the follow up of progressive multifocal leukoencephalopathy in a patient with multiple sclerosis treated with ocrelizumab

## TL;DR

This case report explores the potential of neurofilament light chain as a biomarker for early detection of PML in MS patients treated with ocrelizumab.

## Contribution

The study suggests that serum neurofilament light chain levels may aid in the early diagnosis of PML in MS patients.

## Key findings

- Serum neurofilament light chain levels were elevated at the time of PML diagnosis.
- sNFL levels progressively increased during the patient's follow-up.
- Monitoring sNFL may help detect PML early in MS patients.

## Abstract

Progressive multifocal leukoencephalopathy (PML) results from the reactivation of John Cunningham virus JC virus and is a rare complication of anti-CD20 drug therapy. Neurofilament light chains increasingly serve as a marker of neuroaxonal damage in the follow-up of patients with multiple sclerosis (MS), but its role in the monitoring and detection of processes such as PML is yet to be defined. We report the case of a patient with MS who was treated with ocrelizumab and developed PML. Results: Serum neurofilament light chain (sNFL) levels were elevated at the diagnosis and progressively increased over his follow-up. Our results suggest that the monitoring of sNFL levels may be useful for the early diagnosis of PML in patients with MS.