Objective: To evaluate the diagnostic accuracy of restricted diffusion of the optic nerves in patients with acute optic neuritis (ON).

Materials and Methods: The present study was a diagnostic accuracy study, including all acute ON patients, admitted to Ramathibodi Hospital in Thailand, between January 2014 and December 2018 (ID 075739). Patients were divided into acute ON and non-optic neuritis condition (non-ON) groups. The acute ON group was divided further into neuromyelitis optica spectrum disorder-associated optic neuritis (NMOSD-ON) group and other types of ON (other-ON) group. Patients’ clinical information and MRI scans were reviewed retrospectively. Restricted diffusion of the optic nerves was present if hyperintense signals were observed on diffusion-weighted imaging (DWI) and hypointense signals were observed on the apparent diffusion coefficient (ADC) map.

Results: A total of 102 patients were included in the present study (141 optic nerves). Of all patients, 78 had acute ON (76.5%), and 24 had non-ON (23.5%). Of all optic nerves, there were 95 optic nerves in the acute ON group (67.4%) and 46 in the non-ON group (32.6%). Of 95 optic nerves in the acute ON group, there were 52 optic nerves in the NMOSD-ON group (54.7%) and 43 in the other-ON group (45.3%). Restricted diffusion of the optic nerves demonstrated a sensitivity of 77.9%, specificity of 95.7%, positive predictive value of 97.4%, and negative predictive value of 67.7% in identifying acute ON. It had a sensitivity of 86.5%, specificity of 32.6%, positive predictive value of 60.8%, and negative predictive value of 66.7% in differentiating NMOSD-ON from other-ON.

Conclusion: The diffusion MRI can be a marker of acute ON. The test is most useful for ruling in acute ON when restricted diffusion is positive. However, further investigations might be required in negative tests. Restricted diffusion is positive in several types of ON. It is difficult to differentiate NMOSD-ON from other ON types using diffusion MRI alone.

Keywords: Neuromyelitis optica spectrum disorders, Optic neuritis, Diffusion-weighted imaging, Apparent diffusion coefficient, Restricted diffusion

DOI: doi.org/10.35755/jmedassocthai.2021.02.11631

Received 20 July 2020 | Revised 27 October 2020 | Accepted 29 October 2020