Background and purpose: Neuromyelitis optica (NMO) is an idiopathic mostly relapsing inflammatory disease with attacks on the optic nerves and spinal cord. Whether NMO is a separate disease or a subtype of classic multiple sclerosis (MS) is unclear. Clinically, CSF and MR imaging parameters and histopathologic data suggest that the normal-appearing white matter (NAWM) may be affected in MS but not in patients with NMO. Therefore, we hypothesized that the NAWM in NMO is normal.
Material and methods: We studied prospectively 8 patients with clinically definitive NMO or remitting longitudinal extensive transverse myelitis (LETM) and 8 healthy controls. Ratios of N-acetylaspartate to creatine (Cr) and choline to Cr and the absolute concentrations of the metabolites were measured by chemical shift imaging with a (1)H-MR spectroscopy operating at 3T. All patients with clinically definitive NMO and LETM were found to be positive for NMO-immunoglobin G with a commercially available test.
Results: The metabolic pattern of the NAWM of patients with NMO showed no difference compared with age- and sex-matched healthy controls.
Conclusions: Diffuse white matter damage is absent in NMO.