Advanced MRI techniques
Advanced MRI techniques include brain and spinal cord volumetric analyses, diffusion tensor imaging (DTI), and resting-state functional MRI. These techniques are usually not applied as part of the clinical routine workup in MOGAD patients, and quantitative volumetric and/or microstructural grey and white matter analyses using advanced MRI techniques are few. Recent studies, however, have identified specific changes in MOGAD patients that are potential new imaging biomarkers and tools for a better understanding of MOGAD disease pathology (23,100–102).
Although brain lesion distributions have been found to differ between MOGAD and AQP4-NMOSD patients, brain MRI volumetry did not show any differences in MOGAD patients compared to healthy controls in whole brain, deep grey matter, or white matter volumes (100,103). In children with ADEM, reduced brain volume and failure of age-expected brain growth was found for both MOG-IgG seropositive and -seronegative patients (Bartels et al. submitted), similar to findings in paediatric anti-NMDA-receptor encephalitis and paediatric-onset MS (7,81,104).
Spinal cord MRI analysis could identify spinal cord atrophy in patients with MOGAD as compared to healthy subjects, which was found to associate with increased counts of historical myelitis attacks. However, cord lesion frequency and atrophy was found to be less frequent compared to AQP4-TM (41,101). In MOG-myelitis patients, another study showed that the grey matter volume in the spinal cord was reduced during the acute phase of the attack (102).
Resting-state functional MRI connectivity allows for the study of functional connectivity alterations, such as in the visual or sensorimotor networks of the brain (105–107). Recently, it was found that altered interhemispheric function in patients with MOG-ON can be observed compared to healthy controls using resting-state functional MRI (108).
Meanwhile, evaluating network and CNS changes using graph theory and network statistical methods for elucidating clinical attack-related damage in NMOSD patients has also shown promise. Both cortical topological network changes and deep grey matter volume changes have been detected in AQP4-NMOSD patients following ON attacks and in patients with a simultaneous combination of clinical attacks (109,110). These findings suggest there may be non-localised damage or affection in NMOSD, which could also be the case in MOGAD.
Using DTI, one study found decreased white matter integrity in adult MOGAD patients compared to healthy controls, specifically reduced parallel diffusivity within whole-brain white matter tracts (100). As demyelination represents a pathological hallmark in MOGAD, in-vivo imaging of myelin integrity could represent a promising technique to further identify disease mechanisms and disease courses in MOGAD (111). Further studies applying more advanced sequences representative of myelin, such as T1-weighted/T2-weighted intensity-ratio, multi-parameter mapping, and magnetization transfer MRI analysis in MOGAD patients may help in identifying more subtle MRI changes in the future (112–114).