Table 3.

Characteristics and variables to be extracted from included articles

Characteristics	Variables
Population	Age in years; sex; primary diagnosis; medical specialty; pain history
Intervention (parameters of TENS)	Frequency; intensity, pulse duration, modality, application area, duration of treatment; application interface; time of follow-up
Biochemical parameters	Type of proinflammatory cytokines and evaluation of their expression in blood (level pre and post-intervention)
Methodological information	Sample size, primary endpoint studied (inflammation), other outcomes, randomization, blinding, patient eligibility criteria.