The role of Diffusion Weighted Imaging (DWI) in the diagnosis of Optic Neuritis

Purpose: Optic neuritis (ON) is an acute, demyelinating inflammation of the optic nerve and is frequently the initial presentation of multiple sclerosis (MS), neuromyelitis optica (NMO) and myelin oligodendrocyte glycoprotein antibody disease (MOG).
Orbital MRI is essential in the diagnosis of ON and distinct imaging patterns for these etiologies have been described, based on classic sequences- T2/ STIR and post-contrast T1. In this study we aim to determine the role of Diffusion Weighted Imaging (DWI) in the diagnosis of ON according to the different etilogies.

Methods: We retrospectively reviewed 21 orbital MR scans of 14 patients with MS, NMO and MOG. All 14 patients had orbital MR scans preformed during the acute event. 7 had follow up scans in addition. Imaging parameters evaluated were optic nerve segment involved, nerve width, T2 signal, enhancement and DWI restriction.

Results: 14 patients (11F, 3M; mean 37 years) with acute ON, MS (5), NMO (5) and MOG-AD (4). Initial scans during the acute event showed enhancement and high T2 signal in the involved optic nerve all 14 cases, DWI restriction in 13/14 and nerve swelling in 11/14 . Involvement of the optic nerve papillae noted in 3/5 MS patients, 2/5 NMO and 1/4 MOG cases. Bilateral extensive involvement was noted in 1 MOG case. 3/4 MOG cases showed long retrobulbar optic nerve involvement as well as marked perineuritis. 1/4 MOG cases showed bilateral involvement.
In all 7 Follow up MR scans, nerve swelling resolved. 3/7 showed marked subsequent nerve atrophy (1 NMO, 2 MOG). 6/7 cases showed resolution of signal on DWI (faint residual signal in one NMO case).

Conclusion: Restricted diffusion of the inflamed optic nerve correlates with the degree of acute inflammation and can be used in addition to the conventional sequences to monitor and evaluate disease activity and extension