Increased Thalamocortical Functional Connectivity on Discontinuation of Treatment in Painful Diabetic Peripheral Neuropathy.

Altered functional connectivity has been demonstrated in key brain regions involved in pain processing in painful diabetic peripheral neuropathy. However, the impact of neuropathic pain treatment on functional connectivity does not appear to have been investigated. Sixteen participants underwent resting state functional MRI when optimally treated for neuropathic pain during their involvement in the Optimal Pathway for Treating Neuropathic Pain in Diabetes Mellitus trial and 1 week following withdrawal of treatment. On discontinuation of pain treatment, there was an increase in functional connectivity between the left thalamus and primary somatosensory cortex (S1) and the left thalamus and insular cortex, key brain regions that are involved in cerebral processing of pain. The changes in functional connectivity between scans also correlated with measures of pain (baseline pain severity and Neuropathic Pain Symptom Inventory). Moreover, when participants were stratified into higher- and lower-than-average baseline pain subgroups, the change in thalamic-S1 cortical functional connectivity between scans was significantly greater in those with high baseline pain compared with the lower-baseline-pain group. This study shows that thalamo-cortical functional connectivity has the potential to act as an objective biomarker for neuropathic pain in diabetes for use in clinical pain trials.