Amongst adult patients, ON is the most common manifestation revealing MOG associated disease (MOGAD)25–26. Studies have found that the optic nerve sheath is often affected in MOG-IgG positive optic neuropathy27–31. In this study, 20(51%) patients had OPN. It was also reported that up to 50% of patients were MOG-IgG positive ON21,23. The optic nerve sheath enhancement can be a prominent feature of MOG-IgG associated ON.
There are features of MOG-IgG involvement of the optic nerve that parallel some of the features of previously described idiopathic OPN32. Firstly, MOG-IgG associated ON is often corticosteroid responsive and can be corticosteroid dependent, which is a common feature of idiopathic OPN. Secondly, MOG-IgG positive ON is often associated with optic disc edema with up to 86% of cases having visible optic disc edema, which is usually present in idiopathic OPN1. Thirdly, the optic nerve sheath enhancement can be a prominent feature of MOG-IgG associated ON and is present in up to 50% of patients with MOG-IgG positive ON21,23.
Patients with MOG-IgG positive ON often have severe optic disc edema, bilateral lesions, and are prone to relapse (about 50%)21,22༌28. Moreover, the edema of optic disc is commonly accompanied by hemorrhage. In 39 cases of MOG antibody-positive ON in the present study, 20 (51%) patients had OPN and 21 (70%) eyes had optic disc edema, which is consistent with previous reports. It is possible that the thickening and inflammation of the optic nerve sheath increase the pressure of the local subarachnoid space, leading to the swelling of the optic disc16. Of the total 20 patients in the present study, 7 (35%) patients who are relatively young had recurrence. However, there are no significant differences between the recurrent cases and the single attack cases in gender, bilateral onset, initial visual acuity, final visual acuity, edema of optic disc, lesions in head and spinal cord, immunotherapy, or initial titer of MOG antibody, which may be due to the small patient population size and the relatively short follow-up time.
In the present study, 25 eyes among the total 30 eyes showed longitudinally extensive optic nerve sheath lesions, which indicates that the lesions of optic nerve sheath in MOG antibody positive OPN are often long segment lesions. Five eyes had orbital tissue enhancement, which were different from multiple sclerosis (MS) related ON lesions. This is also consistent with previous research reports21,33. One patient had occipital lobe lesions, but no lesions in the intracranial segment of the optic nerve and the optic chiasm were seen. This is different from previous reports22.
All of our 20 MOG antibody positive OPN patients were treated with high-dose intravenous methylprednisolone in acute phase, followed by slowly-reduced oral prednisolone. At the onset, 17 (57%) eyes had SVL. At the last follow-up, only 4 (13%) eyes had SVL, and 27 (90%) eyes had significant improvement or improvement in visual acuity. The same situation also occurs in ON patients, at onset 20(61%) eyes and at follow-up 3 (9%) eyes had SVL. This indicates that MOG antibody positive OPN and ON often leads to severe visual dysfunction, but it is well responsive to corticosteroids treatment, and the outcome of the visual functions is optimistic, which is supported by previous studies18,21༌28༌30༌34.
Of the 20 OPN patients, seven cases were given immunotherapy, and only 2 cases had recurrence after taking immunotherapy. It was notable that one patient refused to use immunotherapy and relapsed 9 times. These observations suggest immunotherapy is preventive for relapse. The recurrence rate of OPN (7/20, 35%) was higher than ON (4/19, 21%), this suggesting that MOG-positive OPN may be more relapse than ON.
Of the 20 patients, 3 cases had clinical manifestations similar to those of chronic relapsing inflammatory optic neuropathy (CRION) but showed good responsiveness to corticosteroids therapy. This suggested the necessity for differential diagnosis of MOG antibody positive OPN from CRION. Furthermore, the MOG antibody test should be performed in time to avoid the delay of proper treatment.
MOGAD is an autoimmune inflammatory CNS demyelinating syndrome which presents as optic neuritis, myelitis, encephalitis and acute disseminated encephalomyelitis (ADEM)20,22༌35. Meningitis and cortical encephalitis have been seldomly reported36–39. In Jarius’s study40, Brainstem involvement is present in around one third of MOG-IgG-positive patients with ON and/or myelitis. However, in our 39 patients, there are no brainstem involvement, including initial and recurrent cases. This may be related to the fact that we enrolled mainly patients with optic neuropathy, but the patients who relapsed also did not have brainstem encephalitis, indicating that the incidence of brainstem encephalitis in our group of patients is relatively rare.
In the present study, one of the MOG antibody positive OPN patients was diagnosed with meningoencephalitis. The MRI showed that the left temporal horn was narrowed, and the insula and hippocampus were slightly wider than the opposite side. However, no meningeal involvement and enhanced lesions were observed, which may be because the MRI was performed more than 20 days after the onset, and at that time, the symptoms such as fever and headache had disappeared, and the meninges were not strengthened. Further investigation in this new subtype of MOG antibody disease is warranted.