Background and aims:
The extensive mutual co morbidity of chronic pain and major depression disorder (MDD) is not well characterized.
Methods:
Experimentally induced hyperalgesia was assessed in 38 acute/remitted MDD patients, 51healthy subjects by two human surrogate models, namely repeated strong heat stimulation (60 x 48°C for 6 s, RHS) and by electrical high-frequency stimulation - 5 x 1 s trains at 100 s and 10x detection threshold; HFS). Pain was estimated by numerical rating scales before and after hyperalgesia induction. Hyperalgesia was tested by short heat ramps, electrical stimuli, punctate
stimuli and light touch stimuli in the primary and secondary pain areas. Conditioned pain modulation (CPM) elicited by 3 min cold pressor test was assessed by change of pressure pain threshold.
Results:
MDD patients exhibited significantly increased hyperalgesia in both models to punctate and light touch stimuli in primary and secondary hyperalgesia areas (all p< 0.05), but not enhanced heat hyperalgesia. The magnitude of hyperalgesia correlated significantly with depression and trait anxiety. Medication by monoamine reuptake inhibitors (in half of the MDD patients cohort) mitigated the magnitude of hyperalgesia significantly (p< 0.005). Significant CPM was present in healthy subjects, but not MDD patients.
Conclusions:
Enhanced hyperalgesia in experimental models highlights a risk of exaggerated pain plasticity in MDD patients related to the magnitude of depression and anxiety. This paralleled blunting of the CPM response. Notably, monoamine reuptake inhibitors had a dual effect being an adequate antidepressant treatment but also mitigating pain plasticity.
Funding Deutsche Forschungsgemeinschaft (DFG-CRC 11 58 project B09).

EXAGGERATED HYPERALGESIA AND BLUNTED CONDITIONED PAIN MODULATION IN PATIENTS WITH MAJOR DEPRESSIVE DISORDER