Intermuscular coherence as a candidate biomarker for primary lateral sclerosis

Objective: Reliable and widely accessible neurophysiological biomarkers are needed to assess upper motor neuron (UMN) dysfunction. We investigated whether intermuscular coherence in the beta-gamma frequency range (IMCβγ) and its imaginary component (ICOHβγ) can serve as a biomarker for PLS. Methods: IMCβγ and ICOHβγ were evaluated in upper and lower limb muscle pairs in 21 individuals with PLS along with 42 age- and sex-matched neurotypical control participants. PLS participants underwent clinical evaluations including deep tendon reflex assessment and manual muscle strength testing. Results: IMCβγ and ICOHβγ were significantly lower in PLS patients in both the arms and legs. Area under the receiver-operating characteristic curve ranged between 0.71 and 0.77 for differentiating PLS from neurotypical control participants based on measurements in a single limb. Using an abnormal coherence measurement in any two limbs as a diagnostic test for PLS, test sensitivity was 0.76, specificity was 0.86, and accuracy was 0.83. Conclusions: Both IMCβγ in the arms and ICOHβγ in the legs distinguish PLS patients from neurotypical control participants, supporting their potential as accessible biomarkers of UMN dysfunction.