Spinal Cord Gray Matter Atrophy in Post-Polio Syndrome Tied to Functional Decline

Motor Neurons (Multipolar) with many Processes (mostly Dendrites), Spinal Cord–50X. Shows: 4 multipolar neurons, processes (mostly dendrites), cell bodies, nuclei and neuroglial cells. These motor neurons are located in the anterior (ventral) horn of the spinal cord (gray matter).
Researchers sought to assess the incidence of spinal cord gray matter atrophy in patients with post-polio syndrome and its associations with muscle strength and functional decline.

Spinal cord gray matter (SCGM) that correlated with muscle strength in post-polio syndrome (PPS) is associated with PPS-related functional decline, according to a study published in the European Journal of Neurology.

Neuron damage in acute poliomyelitis is not necessarily evenly distributed or fully visible clinically. Up to 85% of polio survivors develop post-polio syndrome (PPS) years after full or partial recovery from the central nervous system infection with poliovirus. The pathophysiological mechanisms of PPS, which manifests as muscular weakness, pain and fatigue, are not well understood.

The objective of the current study was to evaluate SCGM atrophy in patients with PPS.

Twenty patients diagnosed with PPS who fulfilled March of Dimes criteria and 20 age- and sex-matched healthy control individuals participated in the study (ClinicalTrials.gov Identifier: NCT03561623). They underwent 3T axial 2D- radially sampled Averaged Magnetization Inversion Recovery Acquisitions (rAMIRA) magnetic resonance imaging (MRI) at the intervertebral disc levels C2/C3-C6/C7, T9/T10, and Tmax.

Eleven patients experienced PPS as new muscular weakness or atrophy; 2 experienced new abnormal muscular fatigue; 5 reported aggravations of persisting symptoms; 2 reported it as reactivation of previously resolved symptoms; and 20% of patients experienced respiratory failure at the initial infection.

Patients with PPS had less SCGM at the interverbal disc levels close to the cervical and lumbar enlargements (C2/C3, C3/C4, C4/C5, C5/C6, and Tmax) compared with healthy control individuals.

Controlling for pain, depression, and fatigue, the researchers found through dynamometry in myotomes that SCGM area at C2/C3, C5/C6, and Tmax remained significant predictors for neck flexion strength, wrist extension strength, and ankle dorsiflexion strength, respectively.

Adjusting for age and sex in multivariable regression analysis, the researchers found that patients with symptomatic upper limb (UL) paresis during initial infection had more cervical SCGM atrophy at levels C3/C4, C4/C5, and C5/C6 compared with the control individuals.

Those without symptomatic UL paresis at that time showed cervical SCGM atrophy solely at C4/C5.

Those with PPS-related new or worsening UL motor function had significantly reduced SCGM areas at the levels C3/C4, C4/C5, C5/C6 and C6/C7 compared with healthy control individuals.  After adjusting for severity of initial infection (based on respiratory failure or number of affected regions). the researchers found these patients had significantly reduced SCGM areas compared with stable patients at C4/C5 and C5/C6.

SCGM atrophy was not associated with age or time since acute infection, the researchers found in multivariable regression analysis, adjusting for severity of the initial infection based on regions involved.

Study limitations included its cross-sectional study design only relying on 1 center, a small sample size, and the lack of direct comparison between rAMIRA and other SC imaging approaches.

The researchers concluded, “Patients with PPS show significant SCGM atrophy, particularly at levels close to the cervical and lumbar enlargements. Even after adjustment for the level of depression, fatigue and pain, potential confounding symptoms frequently observed in PPS, SCGM atrophy is significantly and segment-wise associated with muscle strength in corresponding myotomes. Moreover, SCGM atrophy is associated with patient-reported PPS-related functional decline.”

Reference

Wendebourg MJ, Weigel M, Richter L, et al. Spinal cord gray matter atrophy is associated with functional decline in post-polio syndrome. Eur J Neurol. Published online February 1, 2022. doi: 10.1111/ene.15261