Changes in brain functional connectivity associated with ongoing neuropathic pain in patients with painful...

To assess changes in brain functional connectivity associated with the painful nature of peripheral polyneuropathy.

Resting-state functional magnetic resonance imaging (rs-fMRI) was performed in 26 patients with painful or painless polyneuropathy. According to previously published results, connectivity was studied regarding the default mode network (DMN), intrathalamic and thalamocortical connections, and, the different brain networks (pain matrices) involved in the "nociceptive", "attentional" and "emotional" aspects of the chronic pain experience.

No change in DMN connectivity was found between groups. Thalamocortical connectivity was reduced in patients with painful polyneuropathy, especially for the thalamic cluster connected to the motor cortex, while intra-thalamic (mediolateral) connectivity was increased in patients with painless polyneuropathy. Intra-connectivity was increased within the pain matrices, especially the "nociceptive" matrix, in patients with painful polyneuropathy, while inter-connectivity was increased between the "attentional" and "emotional" pain matrices in patients with painless polyneuropathy. Increased connectivity between the posterior insula and parietal operculum positively correlated with the neuropathic pain symptom score and impact of pain on daily functioning.

Painful polyneuropathy was characterized by increased intra-connectivity within each pain matrix and reduced thalamocortical connectivity of certain thalamic clusters, notably linked to the motor cortex. Conversely, painless polyneuropathy was characterized by increased connectivity within the thalamus and between the different pain matrices. Although various methodological limitations must be acknowledged (small sample size, lack of a control group of healthy subjects or measurement of pain intensity during neuroimaging examination), these results provide new information on the changes in brain connectivity associated with painful polyneuropathies. This study also brings new arguments to explain the efficacy of motor cortex stimulation in the treatment of chronic neuropathic pain.