Early anisotropy changes in the corpus callosum of patients with optic neuritis

Optic neuritis (ON) and any other early manifestation of multiple sclerosis (MS) are referred to as clinically isolated syndrome (CIS) as long as MS is suspected. In this prospective study we aimed to determine whether diffusion tensor imaging (DTI) could quantify structural changes in patients with early MS. A total of 24 patients and 15 control subjects were prospectively followed by clinical examinations and MRI. the main inclusion criterion was presentation with ON. Patients underwent serial MRI scans: MRI1 (baseline, n=24), MRI2 (mean 6.6 months, n=24), MRI3 (mean 13.0 months, n=14), MRI4 (mean 39.4 months, n=5). Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps were derived from DTI. Four regions of interest (ROIs) were defined in normal-appearing white matter (NAWM). In the temporal course FA decreased in the genu of the callosal body (GCC) from MRI1 to MRI4 (P=0.005) and in the splenium of the callosal body (SCC) (P=0.006). Patients already had lower FA values in the SCC (P<0.01) on MRI1 compared with the controls. Patients had lower FA values in the GCC (P<0.01) starting from MRI2. Patients with definite MS on follow-up (n=9) showed a correlation between FA in the SCC and time (r=-0.40, P=0.004), whereas patients without progression did not. Our findings suggest that the corpus callosum is an early site for development of anisotropy changes in MS patients with ON. There seems to be a primary FA decrease in all patients with ON that only deteriorates in the group developing definite MS. (orig.)