Clinical implication of serum biomarkers and patient age in inflammatory demyelinating diseases

Objectives Serum synaptic proteins levels may change with age-related neurodegeneration, affecting their clinical implications as a disease biomarker. We aimed to investigate neuronal and astroglial markers in patients with multiple sclerosis (MS) and aquaporin-4 antibody-seropositive neuromyelitis optica spectrum disorders (NMOSD) to compare the clinical implications of these markers according to age. Methods Using single-molecule array assays, we measured neurofilament light (NfL) and glial fibrillary acidic protein (GFAP) in sera from consecutive patients with MS (n = 117) and NMOSD (n = 63). For each disease, we assessed correlations between these markers and disease severity (Expanded Disability Status Scale [EDSS]) scores according to three age groups (<= 44, 45-54, and >= 55 years). Results Although serum GFAP levels were significantly higher in patients with NMOSD than those with MS, levels of both serum markers revealed significant positive correlations with EDSS scores in both diseases. In MS patients, the degrees of correlation between serum NfL (or GFAP) levels and EDSS scores were similar across all age groups. However, in NMOSD patients, positive GFAP-EDSS correlations were distinctively stronger in the youngest than in the oldest group. Conversely, there were no positive NfL-EDSS correlations in NMOSD in the youngest group, but there were significant in the oldest group. Interpretation The degrees to which serum NfL and GFAP levels reflect disease severity vary significantly with patient age in NMOSD, but not in MS. These findings suggest that the pathological processes and progression differ between the diseases; hence, serum biomarker levels may need to be interpreted differently according to patient age and disease type.