PPS, a late-onset neurological disorder following paralytic poliomyelitis, is characterized by new or progressive muscle weakness, fatigue, pain and functional decline. Although global vaccination efforts eradicated poliomyelitis in many regions, recent reports indicate a concerning resurgence. The underlying pathophysiology of PPS is still incompletely understood. Recent work suggested that SCGM atrophy, an estimate of LMN loss, is more pronounced in pwPPS with motor decline, independently of initial infection severity.

33 pwPPS and 33 age- and sex-matched HC underwent 3T axial 2D-rAMIRA spinal cord MRI at the intervertebral disc levels C2/3–C6/7. SCGM areas were segmented with spinal cord toolbox (spinalcordtoolbox.com). Electrophysiological markers of motor unit size (Motor Unit Size Index, MUSIX) and, in a subgroup, serum neurofilament light chains (sNfL) were assessed using SIMOA Human Neurology 2-Plex assay (www.quanterix.com).

Compared to HC, pwPPS showed significantly reduced SCGM areas at C2/3 (p<0.0001), C3/4 (p=0.0002), C4/5 (p<0.0001), C5/6 (p<0.0001) and C6/7 (p<0.0001). SCGM areas at the intervertebral disc level C6/7, corresponding to cord segment C8, were significantly inversely correlated with MUSIX values of C8-innervated musculature (r=-0.40, p=0.042). Persons within the highest MUSIX tertile showed reduced SCGM areas compared to those within the lowest tertile, adjusted for age and sex (11.8 mm² vs. 14.4 mm², p= 0.014). sNFL levels were not significantly increased in pwPPS (mean z-value adjusted for age and BMI: 0.2, SD 0.99).

This study provides evidence that pwPPS show cervical SCGM atrophy, which is inversely correlated to the electrophysiological marker of motor unit size, likely explained by compensatory reinnervation as adaptive response to LMN loss.