Ten studies were included: seven RCTs (n=465, range 21 to 313); one CCT (n=15); and two follow-up trials (n=19, n=32). All studies had some methodological flaws including; not accounting for seasonal temperature effects (three studies); mostly female participants; inconsistent reporting; outdoor temperature considered as a confounding factor; ineffective training methods for biofeedback; and a lack of comparison of thermal biofeedback with a control group.
Six studies showed that thermal biofeedback did not provide better outcomes to other types of relaxation, classical conditioning, non-thermal biofeedback or a calcium channel blocker. Two studies reported problems in teaching hand warming skills and neither found any benefit of thermal biofeedback compared with a no treatment or placebo control.
Two small RCTs found that thermal biofeedback provided greater reductions in symptom frequency compared with either autogenic training or electromyography. Both these studies were considered to be the highest quality and showed statistically significant differences favouring thermal biofeedback for hand warming and reductions in attacks. The largest RCT showed no evidence of a reduction in attacks compared with control biofeedback and an increase in attacks compared with a calcium channel blocker.