The inhibitory effect of conditioned pain modulation on temporal summation in low-back pain patients

The literature on conditioned pain modulation (CPM) is inconclusive in relation to low-back pain and it is unclear how CPM affects temporal summation as a proxy of central pain integration. The aim of this study was to examine whether the CPM effect would be different on pain induced by temporal summation than single stimuli in a group of low back pain patients. A total of 149 low-back pain patients were included. CPM was examined using single, repeated and temporal summation (repeated-single difference) of mechanical pressure pain as test stimuli at an individualized, fixed supra-pain-threshold force, before and after 2 min of cold pressor test (0-2 degrees Celsius). Participants were categorized as CPM responders or non-responders according to three different criteria: simple (any pain inhibition), strict (pain inhibition of more than 10VAS) and reversed (pain inhibition or facilitation of less than 10VAS). Clinical data on back pain was collected for correlation and descriptive purposes. Significant modulation was observed for all three test stimuli. Effects sizes were comparable in relative terms, but repeated pressure pain modulation was greater in absolute terms. No correlations to clinical data were observed, for any measure. The current data suggests that repeated pressure pain may be better suited as the CPM test stimuli, than single pressure pain and temporal summation of pressure pain, as the CPM effect in absolute terms was greater. Employing temporal summation as the test stimulus in a CPM paradigm may be more sensitive than a single test stimulus.