Increased spinal pain sensitization in major depressive disorder: A pilot study.

Although patients suffering from major depressive disorder (MDD) often complain from painful symptoms, the relationship between experimental pain processes and depression has yet to be clearly characterized. Only recently have studies employing temporal summation (TS) paradigms offered preliminary insight into the co-occurrence of pain and depression. This study sets out to evaluate the contribution of spinal and supraspinal processes in pain sensitization in MDD using a TS paradigm. Thirteen volunteers with no psychiatric disorders (controls) and fourteen MDD subjects were included in the analysis. Low-(0.14Hz) and high-(1Hz) frequency intermittent stimulations of the sural nerve were used to induce TS. Spinal pain sensitization was quantified by measuring the change in the amplitude of the nociceptive-specific flexion reflex (NFR) response, and supraspinal pain sensitization was obtained by measuring change in subjective pain rating, from the low- to high-frequency stimulation condition. We found an increased sensitization in the NFR response (p<0.05) in MDD subjects in the high-frequency condition, which did not translate into an increase of their subjective responses. However, we found a positive association between spinal sensitization and painful somatic symptoms in MDD subjects. Together, these results suggest increased spinal pain sensitization in MDD, which might explain the high prevalence of painful somatic symptoms in these patients.