Astrocytic damage is far more severe than demyelination in NMO
A clinical CSF biomarker study

Introduction: Loss of aquaporin 4 and glial fibrillary acidic protein (GFAP) with necrosis and demyelination is a prominent pathologic feature of neuromyelitis optica (NMO). However, the clinicopathologic significance of astrocytic damage and its relation with demyelination are unknown.

Objective: To analyze clinical and pathologic values of a CSF biomarker of astrocytic damage in NMO.

Methods: We measured the levels of GFAP, S100B, myelin basic protein (MBP), and neurofilament H (NF-H) in CSF obtained from patients with NMO (n = 33), multiple sclerosis (MS) (n = 27), acute disseminated encephalomyelitis (ADEM), ischemia, meningitis, and other neurologic disease controls (OND).

Results: The CSF-GFAP levels during relapse in NMO (2,476.6 ± 8,815.0 ng/mL) were significantly higher than those in MS (0.8 ± 0.4 ng/mL) and OND (0.7 ± 0.5 ng/mL), and much beyond those in ADEM (14.1 ± 27.4 ng/mL). The sensitivity and specificity of CSF-GFAP for NMO was 90.9% and 76.9% in all, but the specificity improved above 90% in cases limited to demyelinating diseases. CSF-S100B showed a similar trend but was less remarkable. In contrast, MBP and NF-H are not different between NMO and MS. Following treatments, the CSF-GFAP rapidly decreased to a normal level, but CSF-MBP remained high. There were strong correlations between the CSF-GFAP, CSF-S100B, or CSF-MBP levels and Expanded Disability Status Scale (EDSS) or spinal lesion length in the acute phase (r > 0.6). Only CSF-GFAP correlated with EDSS at 6-month follow-up (r = 0.51) in NMO.

Conclusions: Astrocytic damage reflected by elevated CSF glial fibrillary acidic protein is a clinically relevant, primary pathologic process in neuromyelitis optica, and is far more severe than demyelination.