Investigating the Presence of Interattack Astrocyte Damage in Neuromyelitis Optica Spectrum Disorder: Longitudinal Analysis of Serum Glial Fibrillary Acidic Protein

OBJECTIVES: Information on subclinical astrocyte damage can provide further insight into neuromyelitis optica spectrum disorder (NMOSD) pathophysiology and disease-monitoring strategies. To investigate whether astrocyte and neuroaxonal damage occurs during interattack periods in individuals with NMOSD through longitudinal measurement of serum glial fibrillary acidic protein (sGFAP) and neurofilament light chain (sNfL) at multiple time points. METHODS: sGFAP and sNfL levels were measured in 187 serum samples from 20 participants with NMOSD treated with rituximab (median follow-up: 24 months) and 19 age-/sex-matched healthy controls using a highly sensitive single-molecule array assay. From the NMOSD cohort of National Cancer Center, Korea, 14 clinically stable participants were randomly selected for focused investigation of interattack periods, and 6 participants with clinical attacks despite treatment were enrolled for attack-related measurements. RESULTS: Significant elevations of sGFAP levels were observed in all clinical attacks, and 95% (19/20) of patients showed reduction of sGFAP levels below the cutoff value (3 SDs above mean levels in age-/sex-matched healthy controls) within 3 months of their clinical attacks. The sGFAP levels were consistently low during interattack periods in 90% (17/19) of patients whose sGFAP levels returned to below the cutoff value. Changes in sNfL levels were similar to but slower than those in sGFAP levels. CONCLUSIONS: Subclinical astrocyte damage represented by increasing sGFAP levels rarely occurred during interattack periods in individuals with NMOSD; however, a certain degree of astrocyte damage did occur at the time of clinical attacks without exception, but it was not evident within 3 months of the attack.