Relapsing antibody-negative patients with features of neuromyelitis optica spectrum disorders: Differences in -acetylaspartate level in the cervical spinal cord indicate distinct underlying processes.

BACKGROUND

Due to lack of biomarkers, antibody-negative patients with features of neuromyelitis optica spectrum disorders (NMOSD) are among the most challenging to diagnose and treat. Using unsupervised clustering, we recently identified 'MS-like', 'spinal MS-like', 'classic NMOSD-like' and 'NMOSD-like with brain involvement' subgroups in this cohort.

OBJECTIVE

We used magnetic resonance spectroscopy (MRS) to examine differences in the level of key metabolites in the spinal cord between the four identified subgroups.

METHODS

Twenty-five relapsing antibody-negative patients with NMOSD features classified by the unsupervised algorithm to one of the subgroups underwent a prospective cervical spinal cord MRS. Spectra from 16 patients fulfilled quality criteria and were included in the analysis.

RESULTS

Total -acetylaspartate (tNAA), but not total choline (tCho) or myo-inositol (Ins), was significantly different between the four subgroups ( = 0.03). In particular, tNAA was 47.8% lower in the 'MS-like' subgroup as compared with the 'classic NMOSD-like' subgroup ( = 0.02). While we found a negative overall correlation between tNAA and disability score ( = -0.514,  = 0.04) in the whole cohort, the disability score did not differ significantly between the subgroups to explain subgroup differences in tNAA level.

CONCLUSIONS

Significant differences in the cervical spinal cord tNAA measurements confirm that the previously identified clinico-radiologic subgroups contain patients with distinct underlying disease processes.