Cerebral MRI
Cerebral MRI changes in MOGAD are highly dependent on age. In children, typical MRI findings of ADEM are found in 40-50% of MOGAD cases (7). These include widespread supra- and infratentorial, asymmetrical diffuse white matter T2-hyperintensive lesions (32,73). Additional bilateral thalamic lesions were more common in MOG-IgG positive compared to MOG-IgG negative ADEM paediatric patients (74). In adults, brain MRI lesions are typically few and often either found infratentorially or presenting as cortical lesions (75,76), however there have been observations of large, confluent T2-hyperintense lesions in the white matter similar to ADEM (11).
Brainstem lesions can be found in up to 30% of adult MOGAD patients (6,77). These lesions are typically poorly demarcated, often located in the pons, around the 4th ventricle, or the cerebellar peduncles and show resolution over time (75). Importantly, isolated brain or brainstem lesions are rare in adults and more often occur in combination with optico-spinal lesions (6). One patient presented with an initial MRI pattern typical of chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids (CLIPPERS) and then subsequently developed LETM leading to a diagnosis of MOGAD (78).
Isolated T2-hyperintense cortical lesions visible on fluid-attenuated inversion recovery (FLAIR) sequences in both adult and paediatric patients with seizures were identified and referred to as FLAMES: FLAIR-hyperintense Lesions in Anti-MOG-associated Encephalitis with Seizures (76,79). In these patients, cerebral MRI demonstrates unilateral or bilateral cortical T2-hyperintense lesions, but can also include deep grey matter, white matter, and brainstem lesions (55,57,80). In paediatric MOG-associated autoimmune encephalitis, cerebral MRI findings include extensive cortical and/or subcortical grey matter involvement without the typical white matter lesions seen in ADEM (4,60). Importantly, cerebral MRI in these children was normal in only 9% of the cohort, which is much less compared to other types of autoimmune encephalitis, such as anti-NMDA-receptor encephalitis where MRI can be normal in around 50% of the patients (81). In young children presenting with the rare leukodystrophy-like MOGAD phenotype, cerebral MRI shows extensive confluent symmetrical white matter lesions with progression over time (61).
Since MOGAD represents an important differential diagnosis from MS and AQP4-NMOSD using radiological features, several studies assessed potential differences on MRI. A distinct pattern of MRI lesions defined by the so-called Matthews-Jurynczyk criteria can help differentiating MOG-NMOSD vs. MS strongly favouring MS over MOGAD, when: i) ≥ 1 lesion adjacent to a lateral ventricle and in the inferior temporal lobe, ii) subcortical U-fibre lesions, and iii) Dawson’s finger-type lesions (75,82,83). However, these studies did not report criteria to help discriminate between MOGAD and AQP4-NMOSD patients (84). The brainstem is a location where both MOGAD and AQP4-NMOSD patients can present with lesions (75,83), while cortical and juxtacortical lesions are more frequently found in MOGAD versus AQP4-NMOSD patients. Moreover, the area postrema syndrome that often affects AQP4-NMOSD patients with its corresponding MRI lesions, is not a characteristic feature in MOGAD (54).