To highlight FLAIR-variable Unilateral Enhancement of the Leptomeninges (FUEL) in patients with myelin oligodendrocyte glycoprotein (MOG)-IgG antibodies, which likely lies on a spectrum of MOG-IgG-positive meningo-cortical syndromes.

In 2017, Ogawa et al. described a unilateral encephalitis with cortical T2-Fluid attenuated inversion recovery (FLAIR) hyperintensity on brain magnetic resonance imaging (MRI), seizures, and MOG-IgG positivity. A literature review characterized unilateral cortical FLAIR-hyperintense Lesions in Anti-MOG-associated Encephalitis with Seizures (FLAMES) as a distinct clinico-radiographic syndrome that frequently presents with headache, fever, seizures, and/or focal cortical symptoms. A subset of these patients had unilateral leptomeningeal enhancement in addition to cortical T2-FLAIR hyperintensity on brain MRI, suggesting a broader disease spectrum with meningeal involvement.

We searched the radiology reports of Mayo Clinic patients who tested positive for MOG-IgG by live cell-based assay using fluorescence-activated cell-sorting, looking for cases of unilateral meningeal and/or cortical abnormalities on brain MRI. 

Through our search we identified two patients with isolated MOG-IgG positivity and unilateral leptomeningeal enhancement: an 11-year-old girl (patient 1) and a 9-year-old boy (patient 2). Both patients were positive for MOG-IgG at a titre of 1:40. Both patients had minimal-to-no adjacent cortical T2-FLAIR hyperintensity, indicating the possibility of FLAIR-variable Unilateral Enhancement of the Leptomeninges (FUEL) in MOG-IgG-Associated Disease (MOGAD). Both patients had optic neuritis at the time FUEL was identified as well as headache, and both had symptomatic resolution after corticosteroid treatment. Patient 1 had three further episodes of optic neuritis, while patient 2 had a previous episode of headache, fever, seizures and left-sided weakness suggestive of unilateral cortical FLAMES. 

We report two cases of FUEL in MOGAD, which likely lies on a clinico-radiographic spectrum with unilateral cortical FLAMES and more fulminant bilateral meningo-encephalitic disease presentations. Improved recognition of these MOG-IgG-positive meningo-cortical syndromes is important to facilitate further study into immunopathogenesis, treatment and prognosis.