Objective To observe the clinical manifestations of 3 cases with myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease and anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis antibody overlapping syndrome (MNOS), aiming to expand the understanding of the clinical spectrum of such syndromes.

Methods Retrospective analysis was performed on the data of 3 patients with MNOS who were positive for both MOG antibodies and NMDAR antibodies. Clinical features, neuroimaging characteristics, and outcomes were collected, and cell-based assay (CBA) technique was used for diagnosis.

Results One case presented both positive MOG antibodies and NMDAR antibodies, but the clinical manifestations were typical symptoms of anti-NMDAR encephalitis. In one case, the clinical and cranial magnetic resonance imaging (MRI) features of demyelinating disease recurred after anti-NMDAR encephalitis, with atypical symptoms of MNOS such as numbness and weakness in limbs, blurred vision, and diplopia. The last case presented both positive MOG antibodies and NMDAR antibodies, but the clinical manifestations were typical symptoms of anti-NMDAR encephalitis. In MNOS, MOG antibody-associated disease and anti-NMDAR encephalitis may appear simultaneously or sequentially, with epilepsy being the most common symptom. Cranial MRI findings showed that the patients presented and mainly involved supratentorial lesions, which may also involve the brainstem, but no spinal cord lesions were found. All patients showed slightly abnormal cerebrospinal fluid. Patients showed a good response to first-line immunotherapy during the acute phase of the disease, with a favorable prognosis. But most patients were prone to relapse.

Conclusion In MNOS patients, anti-NMDAR encephalitis may present with clinical and(or)MRI features of demyelinating disease simultaneously or sequentially. The clinical manifestations of patients are complex and diverse. Patients with atypical symptoms require to improving the understanding of MNOS and timely treatment.