Inflammatory demyelination in the anterior optic pathway, including the optic chiasm (OC), occurs frequently in relapsing-remitting multiple sclerosis (RRMS), aquaporin4 (AQP4) antibody (Ab) positive neuromyelitis optica spectrum disorder (NMOSD), and myelin oligodendrocyte glycoprotein-Ab associated-disease (MOGAD).
To evaluate the involvement of the OC in RRMS, AQP4-NMOSD and MOGAD using Magnetization Transfer Ratio (MTR) and explore its relationship with prior optic neuritis (ON).
We recruited 25 patients with RRMS (16 F, mean age: 44.6 yrs ±11.8, median EDSS: 2.0 [range: 1.0-7.5], mean number of previous episodes of ON: 0.44±0.58, 9 unilateral, 1 bilateral), 13 with AQP4-NMOSD (10 F, mean age: 45.3 yrs ±11.2, median EDSS: 3.0 [1.0-6.5], mean number of ON episodes: 1.54±1.13, 4 unilateral, 6 bilateral), 20 with MOGAD (13 F, mean age: 33.9 yrs ±16.4, median EDSS: 2.0 [0.0-6.5], mean number of ON episodes: 2.85±2.80, 6 unilateral, 11 bilateral) and 29 healthy controls (HC) (23 F, mean age: 35.9 yrs ±12.8). We used T2-weighted, MTon and MToff images to obtain MTR maps of the OC. Age-, sex-, and disease duration-adjusted linear regression models were used to compare the measures between disease and healthy groups (p<0.05).
Chiasmal MTR values in patients with previous ON were lower in AQP4-NMOSD (p=0.040) and MOGAD (p=0.001) than HC but not when compared to patients without previous ON. In patients with RRMS and previous ON, MTR values were lower than patients without prior ON (p=0.003). No differences were found either between patients without ON and HC or between the disease groups.
When considering all patients with demyelinating diseases, patients with previous ON had lower chiasmal MTR values when compared to HC (unilateral: p=0.037; bilateral: p=0.002) and to patients without ON (unilateral: p=0.019; bilateral: p<0.001). This difference persisted when comparing both monophasic and relapsing ON patients to HC (p=0.044; p<0.001) and to patients without ON (p=0.019; p<0.001). No differences were found between patients without history of ON and HC. A correlation was found between MTR values and number of ON episodes (rho=-0.55, p<0.001).
Microstructural damage in the OC correlated with the number of ON episodes across inflammatory demyelinating diseases. A higher number of episodes is associated with lower chiasmal MTR, supporting its role as an accessible target for the assessment of the visual pathway in inflammatory diseases.