The following is a summary of “Unaltered responses of distal motor neurons to non-targeted thoracic spinal cord stimulation in chronic pain patients,” published in the October 2024 issue of Pain by Riera et al. 

Researchers conducted a retrospective study to analyze the effects of Spinal cord stimulation (SCS) waveforms on motor neuron recruitment in the lower limbs of individuals with chronic pain.  

They performed isometric ankle dorsal flexions at various force levels under 4 SCS conditions: SCS Off (1 week), burst SCS (40 Hz), SCS Off (acute), and tonic SCS (130 Hz). Muscle activity was noted by high-density surface electromyography (64-electrode grid) on the tibialis anterior (TA) muscle. Motor unit (MU) action potentials were examined for recruitment and de-recruitment thresholds, discharge rate, inter-spike interval, and common synaptic input.   

The results showed 9 individuals (5 females; 4 males; mean age 59) with chronic pain undergoing thoracic (Th7–Th8) epidural spinal stimulation, a total of 97 MUs were identified at 15% maximal voluntary torque (MVT) and 83 MUs at 30% MVT, averaging 10.8 ± 3.7 at 15% MVT and 10.4 ± 3.5 at 30% MVT. While some subject-specific variations were noted, the study indicated that different SCS frequencies did not significantly affect MU discharge characteristics in the TA muscle among participants, with P values at 15% MVT being 0.586 (Chi²= 1.933), 0.737 (Chi² = 1.267), 0.706 (Chi² = 1.4), and 0.586 (Chi² = 1.933). The P values from the Friedman test at 30% MVT were 0.896 (Chi² = 0.6), 0.583 (Chi² = 1.95), 0.896 (Chi² = 0.6), and 0.256 (Chi² = 4.05) and no significant differences were observed among the different stimulation types for the delta (0–5 Hz), alpha (5–12 Hz), and beta (15–30 Hz) frequency bands at both force levels.  

They concluded SCS with different waveforms (tonic/burst) did not significantly influence motor neuron recruitment in non-motor individuals with chronic pain, as there were no changes in MU oscillatory activity at any low or high bandwidths. 

Source: link.springer.com/article/10.1007/s40122-024-00670-x#Abs1