A new study helps make clear what’s happening in the visual systems of patients with pediatric onset multiple sclerosis.
Patients with pediatric onset multiple sclerosis (POMS) begin exhibiting vulnerability in the extrastriate visual system, even though they are young in age and tend to have mild disability, according to new research.
Writing in the journal Human Brain Mapping, investigators from the Children’s Hospital of Philadelphia said they found decreases in visual gamma power, cuneus volume, and mean fractional anisotropy (FA) of the optic radiations in POMS subjects.
Corresponding author Amy Waldman, MD, and colleagues wrote that POMS tends to look similar to relapsing remitting MS (RRMS) in adults. Key differences, however, are that younger patients tend to have more relapses early in disease, and they do not have the same comorbidities or impacts of prolonged diseases that are evident in adult patients.
“In aggregate, it can be argued that study of POMS provides a view of the earliest impacts of MS pathobiology,” they wrote.
Previous research into the topic led Waldman and colleagues to hypothesize that white matter (WM) integrity might be an early indicator of POMS and that disruption of WM tracts could lead to anterograde loss of cortical tissue.
To test their hypothesis, the team recruited 14 patients with POMS and 15 healthy controls. The enrollees were assessed for visual gamma (30-80 Hz), motor gamma (60-90 Hz), and motor beta (15-30 Hz) cortical oscillatory responses to a visual-motor task. The subjects then underwent subsequent analysis using 3T MRI.
“Visual gamma band power was reduced in POMS and was associated with reduced FA of the optic radiations but not with loss of cuneus volume or thickness,” Waldman and colleagues wrote. “Activity in the primary motor cortex, as measured by post-movement beta rebound amplitude associated with peak latency, was decreased in POMS, although this reduction was not predicted by structural metrics.”
The authors said that they did not find a difference between the control group and the POMS group in terms of cuneus thickness, though cuneus volume was decreased in patients with POMS. They also did not find a link between cuneus volume and visual gamma power in either group.
“We acknowledge that, while the cuneus is the primary region responding to visual stimuli, other cortical regions and intercortical region communication likely contribute,” they said. “Our small sample size precluded whole brain analytical methods, although such anamnestic methods will be a priority for future work.”
The authors found that post-movement beta rebound (PMBR) amplitude associated with peak latency was higher in the control group than in the POMS group, which they said could have to do with reduced neuronal density or decreased neuronal excitability.
“However, unlike the visual system, differences in PMBR amplitude could not be explained in the POMS group by variations in corticospinal tract FA or primary motor cortex volume or thickness,” they said. “Primary motor cortex thickness and volume were not statistically different between groups, although both were decreased in the POMS group.”
Waldman and colleagues closed by writing that it is yet unclear how their findings impact higher order visual and motor performance. They say additional research into that question is warranted.
Waldman AT, Sollee JR, Datta R, et al. Structural correlates of atypical visual and motor cortical oscillations in pediatric-onset multiple sclerosis. Hum Brain Mapp. Published online July 10, 2020. doi:10.1002/hbm.25126