The diagnosis of autoimmune encephalitis should be considered in patients with rapid progression (<3 months) of short-term memory loss, decreased or altered level of consciousness, lethargy, personality change, or psychiatric manifestations in association with at least one of the following criteria: new-onset seizures or focal CNS symptoms, CSF pleocytosis, or MRI features suggestive of brain inflammation. Many alternative causes of encephalitis can be excluded after a careful clinical history and evaluation of the CSF, brain MRI, and routine blood tests. Some types of encephalitis can be suspected before receiving the results of neural antibodies, according to the clinical presentation (for instance, faciobrachial dystonic seizures in anti-LGI encephalitis, or psychotic manifestation in anti-NMDAR encephalitis) or brain MRI features (temporal lobe involvement in limbic encephalitis). Antibody testing may show false positive and negative results, particularly when only serum is examined, results are not confirmed with additional laboratory studies, or the test is used indiscriminately without selection of patients.

This chapter focuses on the MOG-antibody-associated disease as a distinct neurological disorder that includes several demyelinating syndromes, and it follows a monophasic or more frequently a relapsing–remitting course. In children, MOG antibody-associated disease usually presents as acute disseminated encephalomyelitis (ADEM), ADEM variants, or encephalitis that may present with seizures and isolated or predominant cortical hyperintense lesions in FLAIR MRI studies (FLAMES). In teenagers and adults the common clinical presentation is optic neuritis, myelitis, or brainstem syndromes. Some of the patients fulfil criteria of neuromyelitis optica spectrum disorders (NMOSD). Persistence of MOG antibodies is common in patients with relapses. The optimal treatment to prevent relapses has not been established. ADEM is the most frequent autoimmune encephalitis in children. The syndrome was characterized before the description of MOG antibodies and associates with distinct clinical and neuroimaging features. Brain MRI shows multiple hyperintense T2 lesions similar to those seen in anti-GABAaR encephalitis. As occur with NMOSD, ADEM is probably caused by different pathogenic mechanisms as MOG antibodies are only found in ~60% of patients. Besides MOG antibody-associated disease there are two other antibody-associated neurological syndromes that target oligodendrocytes as part of an immune attack: anti-NMDAR encephalitis and paraneoplastic encephalomyelitis with CRMP5 antibodies.