Newly Studied Neurological Impact of Polio Could Have Implications for SMA

Researchers are offering new insight into the neurological impact of polio, suggesting the now relatively rare condition impacts not just the spinal cord but also the brain.

The researchers assert that the findings could have far reaching implications that extend beyond polio, as they suggest corticomuscular coherence (CMC) could be a potential biomarker of altered motor network function in other conditions, such as spinal muscular atrophy.

“Our research findings show for the first time that the brain ‘rewires’ in those who suffered from polio in childhood,” said Orla Hardiman, professor of neurology, clinical Medicine, Trinity College, and co-author of the study, said in a statement. “This has implications for our understanding of brain plasticity, and in the longer term for rehabilitation and new biomarker development.”

The study included 24 patients who had polio as children, as well as 11 age-matched controls. Surface electroencephalography (EEG) and electromyography (EMG) were recorded during a pincer grip task, which highlighted differences in CMC between the 2 groups and revealed abnormal coherence patterns in the polio survivors.

For example, the polio survivors did not exhibit the typical beta-band CMC over contralateral motor area. The CMC was also scattered and inconsistent across the 5 tested EEG electrodes, 3 muscles, and the frequency bands.

According to the researchers, the difference in CMC among the 2 groups was statistically significant. Among the polio survivors, the significant CMS appeared consistently in the low gamma (31-47 Hz) frequency band across several EEG-EMG channels in not only primary motor areas but also over parietal and frontal areas.

The findings indicate that CMC patterns between the 2 groups differ in both frequency and location.

“The observation of alterations in corticomotor circuity following poliomyelitis has implications for other conditions, notably spinal muscular atrophy (SMA), for which quantitative biomarkers of drug efficacy are urgently required,” wrote the researchers. “In conditions such as SMA, for example, a consistent abnormal CMC measure in (adult) SMA, could be used as a potential biomarker to track network function. Such biomarkers can identify network-level changes associated with lower motor neurons following administration of a disease modifying agent, thus providing a quantitative biomarker of efficacy in clinical trials.”

According to the researchers, recent imaging studies have implicated altered cortical connectivity in patients with SMA, suggesting that CMC changes are a generic compensatory physiologic reorganization of cortical circuitry following damage to the lower motor neuron.

Reference

Coffey A, Bista S, Fasano A, et al. Altered supraspinal motor networks in survivors of poliomyelitis: A cortico-muscular coherence study. Clin Neurophysiol. 2021;132(1):106-113.