Literature Review

Serum levels of neurofilament light are increased before clinical onset of MS


 

FROM JAMA NEUROLOGY

Serum levels of neurofilament light (NfL) are elevated as long as 6 years before the clinical onset of multiple sclerosis (MS), according to research published in the January issue of JAMA Neurology. These results lend weight to the idea that MS has a prodromal phase, and this phase appears to be associated with neurodegeneration, according to the authors.

Patients often have CNS lesions of various stages of development at the time of their first demyelinating event, and this finding was one basis for neurologists’ hypothesis of a prodromal phase of MS. The finding that one-third of patients with radiologically isolated syndrome develop MS within 5 years also lends credence to this idea. Diagnosing MS early would enable early treatment that could prevent demyelination and the progression of neurodegeneration.

Researchers compared presymptomatic and symptomatic samples

With this idea in mind, Kjetil Bjornevik, MD, PhD, a member of the neuroepidemiology research group at Harvard TH Chan School of Public Health in Boston, and colleagues evaluated whether serum levels of NfL, a marker of ongoing neuroaxonal degeneration, were increased in the years before and around the time of clinical onset of MS. For their study population, the investigators chose active-duty U.S. military personnel who have at least one serum sample stored in the U.S. Department of Defense Serum Repository. Samples are collected after routine HIV type 1 antibody testing.

Within this population, Dr. Bjornevik and colleagues identified patients with MS who had at least one presymptomatic serum sample. The date of clinical MS onset was defined as the date of the first neurologic symptoms attributable to MS documented in the medical record. The investigators randomly selected two control individuals from the population and matched them to each case by age, sex, race or ethnicity, and dates of sample collection. Eligible controls were on active duty on the date of onset of the matched case.

Dr. Bjornevik and colleagues identified 245 patients with MS. Among this sample, the researchers selected two groups that each included 30 cases and 30 controls. The first group included patients who had provided at least one serum sample before MS onset and one sample within 2 years after MS onset. The second group included cases with at least two presymptomatic serum samples, one of which was collected more than 5 years before MS diagnosis, and the other of which was collected between 2 and 5 years before diagnosis. The investigators handled pairs of serum samples in the same way and assayed them in the same batch. The order of the samples in each pair was arranged at random.

Levels were higher in cases than in controls

About 77% of the population was male. Sixty percent of participants were white, 28% were black, and 6.7% were Hispanic. The population’s mean age at first sample collection was approximately 27 years. Mean age at MS onset was approximately 31 years.

For patients who provided samples before and after the clinical onset of MS, serum NfL levels were higher than in matched controls at both points. Most patients who passed from the presymptomatic stage to the symptomatic stage had a significant increase in serum NfL level (i.e., from a median of 25.0 pg/mL to a median of 45.1 pg/mL). Serum NfL levels at the two time points in controls did not differ significantly. For any given patient, an increase in serum NfL level from the presymptomatic measurement to the symptomatic measurement was associated with an increased risk of MS.

In patients with two presymptomatic samples, serum NfL levels were significantly higher in both samples than in the corresponding samples from matched controls. In cases, the earlier sample was collected at a median of 6 years before clinical onset of MS, and the later sample was collected at a median of 1 year before clinical onset. The serum NfL levels increased significantly between the two points for cases (i.e., a median increase of 1.3 pg/mL per year), but there was no significant difference in serum NfL level between the two samples in controls. A within-patient increase in presymptomatic serum NfL level was associated with an increased risk of MS.

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