Sunday, December 31st
Dysregulated Pain Processing and Pain Plasticity in Patients with Major Depressive Disorder
We studied pain processing in patients with major depressive disorder (MDD) on several levels to understand whether the depressive condition amplifies pain experience and/or pain plasticity. Quantitative sensory testing revealed that MDD patients exhibited only liminal differences of their somatosensory pattern compared to healthy subjects. In contrast, when challenged by two different experimental models of hyperalgesia human pain-LTP or sustained painful heat exposure) MDD patients responded with similar heat hyperalgesia, but significantly enhanced secondary hyperalgesia and allodynia pointing towards increased central sensitization, which correlated to their degree of anxiety and depression. Importantly, SNRIs mitigated the hyperalgesia dose-dependently to a very relevant degree. Moreover, as tested by conditioning pain modulation, descending pain control shifted significantly towards facilitation in MDD patients. Imaging experiments revealed significantly lower functional connectivity and a complete absence of adaptive engagement of prefrontal cortical areas during the hyperalgesia-inducing sustained heat stimulation. Collectively, the data support the interpretation that MDD patients are prone to respond with exaggerated pain amplification related to an imbalance of their inhibitory vs. facilitatory descending pain control, which may be related to their deficit of prefrontal pain control.