Longitudinal stability of serum neurofilament light chains in psychiatric disorders

Serum neurofilament light (sNfL) is a biomarker of axonal integrity which is elevated in neurodegenerative diseases. Although common psychiatric disorders are not neurodegenerative, some studies have found slightly higher levels of sNfL in psychiatric disorders compared to healthy controls. The reason for this elevation is unknown, and it is unclear whether this difference persists over time, or if it varies in relationship to symptom severity. Longitudinal serum samples and clinical data from a large dataset of psychiatric patients (n = 836; ages 40+, M = 478, F = 358) were obtained from the Signature Biobank at up to four time points over up to 2 years (from emergency room admission to outpatient follow-up or remission). sNfL was measured using SiMoA assay technology. Repeated measures analyses were used to test sNfL over time, adjusting for age, BMI, blood creatinine and sex. Linear regressions were used to test associations between sNfL levels and depression, anxiety and psychosis symptoms. sNfL levels did not change significantly over time for subjects with all 4 available timepoints (n = 73), nor from baseline to the last available timepoint (n = 268). Males had slightly higher sNfL than females (Cohen’s d = 0.38, p = 0.003). Depression, anxiety and psychosis symptoms improved over time, but there were no clinically significant correlations between sNfL and symptom severity. This study did not detect a significant change in sNfL in psychiatric disorders over time, despite overall improvement in symptom severity. These results suggest that the mild elevation in sNfL reported in psychiatric disorders is a disease trait rather than state dependent.