Female Overrepresentation in Low Back-Related Leg Pain: A Retrospective Study of the Autonomic Response to a Minimally Invasive Procedure

Background The newly proposed low back pain treatment requires case classification according to the pain mechanism (nociceptive, neuropathic or nociplastic) to determine the most effective therapeutic approach. However, there is a lack of objective tools for distinguishing these pain mechanisms. The aim of the study was to identify which symptoms, signs, and standard diagnostic parameters would allow predicting the nociplastic pain (NP) subtype among low back leg pain (LBLP) patients. Methods A retrospective analysis of an LBLP case–control study database was carried out. The presence of NP was assumed if the patient presented with myofascial pain syndrome (MPS) and developed a short-term intensive vasodilatation reaction in the perceived lower leg pain area after provocation by a minimally invasive procedure. Clinical data and standard LBLP diagnostic parameters were analyzed to classify patients as NP (+) vs NP (-). Next, to predict NP probability, logistic regression analysis and a diagnostic classification tree were constructed. Results NP was confirmed in 43.75% of LBLP patients. Women represented 95.24% of all NP (+) patients. The diagnostic classification tree indicated that NP was highly probable if the LBLP subject was female and the result of a positive straight leg raise (SLR) test was lower than 45 degrees. If the SLR test result was greater than or equal to 45 degrees, a negative result on the Bragard test would have diagnostic value. This classification tree was approved to a certain extent in the logistic regression model (deviance residuals, min: −1.8519; 1Q: −0.5551; median: −0.1907; 3Q: 0.6565 and max: 2.1058) but should be verified in a larger group of subjects. Conclusion Female sex, but not clinical data or standard diagnostic parameters, is indicative of nociplastic pain in LBLP patients. More sophisticated statistical methods, based on directly measurable parameters, should be proposed to distinguish NP involvement in LBLP.