During the conditioned pain modulation (CPM), the variance of different factors in the active electrical intramuscular stimulation (a-EIMS) have been considered in knee osteoarthritis (KOA) forming the basis of this research. Here, the corticospinal inhibitory systems were augmented via the a-EIMS.

To determine if in knee osteoarthritis (KOA), one session of active electrical intramuscular stimulation (a-EIMS) compared with sham causes an effect on the motor cortex excitability parameters [motor evoked potential (MEP; the primary outcome), short intracortical inhibition (SICI), intracortical facilitation (ICF) and cortical silent period (CSP)] and pain measurements [pain pressure threshold (PPT); visual analog scale (VAS) and change in numerical pain scale (NPS0-10) during the conditioned pain modulation (CPM)-task]. This study also set out to determine if serum brain-derived neurotrophic factor (BDNF) mediates the effect of treatment on the cortical spinal system as assessed by MEP and PPT.

Women with KOA, 50–75-years old received a 30-min session of either sham (n = 13) or a-EIMS (n = 13) with 2 Hz. The pain measures and excitability parameters were measured before and immediately after a-EIMS or sham.

The a-EIMS group compared with sham decreased the MEP by 31,67% [confidence interval (CI) 95%, 2.34 - 60.98]. For the secondary outcomes, the a-EIMS reduced the ICF and increased the CSP but not changed the SICI. The a-EIMS improved the pain reported on VAS, the PPT, and the score of the NPS (0 - 10) during the CPM-task The BDNF was negatively correlated with the PPT (r = −0.56).

The serum BDNF revealed an inverse relationship with PPT independent of the treatment group. These results suggest that a-EIMS enhanced the corticospinal inhibitory systems in cortical and infracortical pain processing sites most likely by bottom-up regulation mechanisms.