Reduction in movement-evoked pain and fatigue during initial Transcutaneous Electrical Nerve Stimulation treatment predicts responders in women with fibromyalgia

Transcutaneous Electrical Nerve Stimulation (TENS) is a safe, economical non-pharmacological adjunctive intervention. Using data from the Fibromyalgia Activity Study with TENS (FAST) we performed a responder analysis to identify predictors of reduced pain and fatigue after 1-month of daily TENS use in women with FM. Women with FM were randomly assigned to active-TENS (2-125Hz; highest-tolerable intensity), placebo-TENS, or no-TENS for 1-month. After the randomized phase, placebo-TENS and no-TENS groups received active-TENS for 1-month. Responders to TENS were defined as those achieving a 30% reduction in movement-evoked pain and/or 20% reduction in movement-evoked fatigue., The predictor model was developed using data from the randomized phase of the active-TENS group (n=103) and validated using data from the placebo-TENS and no-TENS groups after active-TENS for 1 month (n=155). Participant characteristics, and changes in pain, fatigue, and function were assessed as potential predictors using a logistic regression model. Number needed to treat (NNT), and number needed to harm (NNH) calculations were made comparing the active-TENS group to the placebo-TENS and no-TENS groups using an intention-to-treat analysis. Predictors of clinical improvement in pain at 1-month follow-up were initial decrease in pain during the first TENS use and widespread pain index (AUC=0.80; 95%CI: 0.73,0.87). Predictors of clinical improvement in fatigue at 1-month follow-up were marital status, sleep impairment and initial decrease in fatigue during the first TENS use (AUC=0.67; 95%CI: 0.58,0.75). NNT for pain and fatigue ranged between 3.3-5.3. NNH ranged from 20-100 for minor TENS-related adverse events. The current study shows that 1 in 3 women with FM will experience a clinically significant reduction in pain, while 1 in 5 will experience a clinically significant reduction in fatigue with minimal harms. How a person responds to the first TENS treatment predicts response to daily use over of a 1-month period. Trial Number: NCT01888640, Funded by NIH UM1 AR06338, NIH UM1 AR063381-S1, T32 NS045549-12, and K99AR071517.