Endless back pain is one of the most prevalent reported health complaints. About 8 in 10 people suffer from bouts of back pain. But every person has different pain levels, pain modulation and pain inhibitory mechanism. Thence, the pain treatment should also be different to every person. Now the question is, how we can estimate the extents of pain levels? One of the methods used to investigate individual difference in pain inhibition is the conditioned pain modulation (CPM) paradigms. This involves a psychophysical procedure in which conditioning stimulus reduces the perception of a test stimulus, applied to a remote area of the body.

Therefore, a study was conducted to investigate pain intensity and inhibition mechanism by using CPM in CBP patients with different pain extent. In the study, FMS (fibromyalgia syndrome) patient's CPM that reported most consistent, were measured for comparison. Now, depending upon pain drawings and clinical evaluation, patients were classified into chronic widespread back pain (CWP; n = 32), chronic local back pain (CLP; n = 53) and FMS (n = 92). In this study, CPM was measured by the difference in pressure pain threshold (a test stimulus) before and after tonic heat pain (a conditioning stimulus). Herewith psycho-social variables were also measured.

The CPM analysis showed that the pressure pain threshold was significantly increased among CLP patients after tonic heat pain than CWP and FMS patients (P< 0.001). The levels of CPM were same in both CWP and FMS. The CPM was decreased as the number of painful areas (0-10) increased and patients with CBP showed a higher number of painful areas as compared to FMS (P=0.903). Whereas anxiety and depression were less noticeable in CBP as compared to FMS (P<0.01).

Hence, all these findings suggest that CPM dysfunction is related to CWP and not with FMS. Further, the FMS group shows higher psychosocial burden as compared to CWP without FMS. The centrally acting treatments that target endogenous pain inhibition among CLP and CWP patients seem to be more. This indicates the pain extent is higher among patients with CBP.