Progressive Disability in MS Explained?

Erik Greb

August 06, 2021

Differences in lesion evolution may help neurologists distinguish between multiple sclerosis (MS) and other demyelinating disorders in new findings that may help explain differences in disease course, particularly progressive disability in MS.

Results from a retrospective study show that complete resolution of brain lesions on MRI was more common among patients with myelin-oligodendrocyte-glycoprotein-IgG-associated disorder (MOGAD). Complete resolution occurred in 72% of the group with MOGAD, vs 17% of those with multiple sclerosis (MS) and 14% of those with aquaporin-4-positive neuromyelitis optica spectrum disorder (AQP4+ NMOSD) .

Dr Eoin Flanagan

"What we found was, with MOGAD in particular, many of the lesions resolved completely," co-investigator Eoin Flanagan, MBBCh, neurologist, Mayo Clinic, Rochester, Minnesota, told Medscape Medical News. "That fits with MOGAD having a fairly good prognosis and patients not developing much long-term disability with that disease," he said.

The researchers also studied whether scarring may account for the absence of slowly progressive disability among patients with AQP4+ NMOSD and MOGAD compared with patients with MS.

"The differences in scarring that we found will help physicians distinguish these three diseases more easily to aid in diagnosis. More importantly, our findings improve our understanding of the mechanisms of nerve damage in these three diseases and may suggest an important role of such scars in the development of long-term disability in MS," Flanagan said in a statement.

The findings were published online July 14 in Neurology.

Lesion Evolution

MOGAD, AQP4+ NMOSD, and MS are inflammatory demyelinating disorders that share certain manifestations. However, these disorders differ in important ways, including the severity of attacks and their clinical course.

Although patients with MOGAD and AQP4+ NMOSD generally have severe attacks that bring major disability, the clinical course of these disorders is better than initial attacks would suggest. In contrast, patients with MS have comparatively mild attacks that are associated with a high risk for progressive disability.

Previous studies of these demyelinating disorders have examined shape and location of lesions but not change over time. Observing these lesions' development and resolution could provide information about disease course and influence treatment and the monitoring of disease activity, the current researchers note.

They retrospectively identified consecutive patients with MOGAD, AQP4+ NMOSD, or MS who presented to the Mayo Clinic between January 2000 and August 2019. Data from a cohort of patients with MS in Olmsted County, Minnesota, were also included.

Eligible participants had experienced a first brain or myelitis attack, had undergone MRI of the brain or spinal cord within 6 weeks of the attack nadir, and had undergone a follow-up MRI than 6 months after the attack.

Patients who experienced a relapse during follow-up in the same region as the initial attack were excluded. Concomitant brain and myelitis attacks were analyzed separately.

An index lesion was identified for each patient. The index lesion was defined as an acute lesion that provided an anatomic explanation for the clinical symptoms. If multiple lesions were present, the largest of them was chosen as the index lesion. MRIs were examined by neuroradiologists who were blinded to patients' diagnoses and serology results.

Among the 156 participants, 67 had MS (76% women), 51 had AQP4+ NMOSD (80% women), and 38 had MOGAD (45% women). The median age at first attack for the groups was 37, 53, and 25 years, respectively.

In addition, 63 patients had relapsing-remitting MS, two had a single attack of progressive MS, and two had clinically isolated syndrome. No patients with NMOSD or MOGAD had developed progressive disease at final follow-up.

Participants experienced a total of 81 brain attacks and 91 myelitis attacks. Sixteen patients had had both a brain attack and a myelitis attack.

Symptoms corresponding to the index brain lesions were brainstem or cerebellar syndrome (56), encephalopathy or focal symptoms (12), or combinations of these (13). Among patients with an index myelitis attack, 31 had cervical involvement, 21 had thoracic involvement, and 39 had involvement of both regions.

Complete Resolution

Results showed that 72% of patients with MOGAD experienced complete resolution of the brain index lesion, compared with 17% of patients with MS and 14% of patients with NMOSD (P < .001).

Similarly, 79% of the MOGAD group experienced complete resolution of the myelitis index lesion, compared with no members of the MS or NMOSD groups (P < .001 for both comparisons).

Complete resolution of all T2-abnormalities at MRI follow-up was more common in the MOGAD group than in the other two groups.

For brain attacks, complete resolution occurred in 39% of patients with MOGAD, 10% of patients with NMOSD, and 5% of patients with MS. For spinal cord attacks, complete resolution occurred in 79% of patients with MOGAD, vs none of the patients with NMOSD or MS.

Median reduction in T2 lesion area on follow-up axial brain MRI was larger in patients with MOGAD (213 mm2) than in those with NMOSD (104 mm2; P = .02) or MS (36 mm2; P < .001).

Reductions in lesion size on sagittal spine MRI follow-up were similar between the MOGAD (262 mm2) and NMOSD (309 mm2) groups; both experienced greater reductions than the MS group (23 mm2; P < .001).

Lesion Prevention

Flanagan noted that the diagnosis of MOGAD is based on a test for MOG antibody, but sometimes false positive results occur.

"A single follow-up MRI can be useful, showing that if all the lesions went away, you would be more confident that it would be MOGAD," he said.

Study participants with MS experienced less lesion healing than the patients with MOGAD or NMOSD.

"We now have very effective medications in MS to prevent new lesions from occurring," Flanagan said. The study highlights the importance of lesion prevention, "because when you do get a lesion, it does tend to stay and not recover completely," he added.

He noted that the resolution of lesions in the study population may reflect remyelination. Future research examining whether remyelination is more efficient in MOGAD than in the other disorders could possibly lead to new approaches for MS treatment, said Flanagan.

"Maybe some of the MOGAD lesions are from edema. When we use steroids, that tends to resolve and not leave a scar. So, that's another possibility. We'd like to better understand that," he said.

Differences in Pathology

Commenting on the findings for Medscape Medical News, Bruce Cree, MD, PhD, professor of neurology, Weill Institute for Neurosciences, University of California, San Francisco, noted that the study is one of the first to systematically examine and compare MRI lesion evolution across three disease states.

Dr Bruce Cree

"What they put their finger on are differences in the fundamental pathology of these three different diseases," said Cree, who was not involved with the research.

The study's cross-sectional comparison was its main strength, he noted.

"The main weakness, from my point of view, is that in these three disorders, optic nerve involvement is very common," Cree said. "In this paper, no analysis of optic nerve lesions by MRI was performed."

The researchers acknowledge this limitation and explain that they did not have consistent, dedicated orbital imaging for such an analysis.

Cree noted that the findings also provide a reminder that the pathogenesis of MOGAD is not yet clear.

"We know that these anti-MOG antibodies are associated with this demyelinating disorder, but whether these antibodies have a pathogenic role has yet to be clearly demonstrated," said Cree. "What is actually going on within these lesions also is not fully understood."

The finding that MOGAD lesions can resolve completely suggests that repair mechanisms are at work within the brain and spinal cord, he noted.

Being able to understand and comprehend what those mechanisms at work are and why they occur in MOGAD but not in NMOSD or MS "would be of enormous clinical advantage," he said.

The current study also highlights the importance of incorporating imaging into clinical trials that study these rare disorders, especially serial imaging for MOGAD, Cree added.

This imaging is vital not only for developing new treatments but also for understanding the clinical impact of a given medication. "We really need rigorous imaging to be applied to these rare disorders, just as was done with MS," Cree concluded.

The study was funded by the National Institute of Neurological Disorders and Stroke. Flanagan has received research support from MedImmune/Viela Bio. Cree is working with two of the researchers on the steering committee for the N-MOmentum trial of inebilizumab in patients with NMOSD. He has reported no relevant financial relationships.

Neurology. Published online July 14, 2021. Abstract

Follow Erik Greb on Twitter: @MedscapeErik.

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