Functional and Structural Brain Connectivity in Psoriasis Patients and Healthy Controls : a Brain Imaging Study After Exposure To Mentally-induced Itch

While psoriasis has been extensively studied as a prevalent dermatological disease, its impact on central nervous system is relatively unknown. We have employed MRI techniques in order to study the effect of mentally-induced itch and to reveal if any differences exist between psoriasis patients and healthy subjects. Fourteen patients with chronic psoriasis and fifteen healthy controls were asked to watch two itch inducing videos consisting of people scratching themselves in the scanner. Considering functional connectivity, our results showed that an interconnected network of brain regions was more connected in patients than in healthy controls. This network involves many regions among which the cerebellum, the antero-posterior cingulate gyrus, the thalami and the para-hippocampal and hippocampal gyri play a central role. This network mostly gathers regions involved in either itching or chronic pain sensation but not only. We show that this network can be easily divided into two subnetworks for which the variations observed are not in the same proportions when compared to healthy subjects. Our analysis of DTI images showed that chronic itch can also affect the microstructure of white matter by increasing the fractional anisotropy measure in several tracts connecting the above mentioned areas for patients.With cautious interpretations and further replication of these results, we propose that the subnetwork encoding the perception and control of itch sensation is much more affected than the rest of the network representing mentalizing and empathy. With an approach consisting of measuring microstructural changes at a local level in the brain, we also contradict the findings obtained with global measures which stated that chronic psoriasis cannot alter the anatomy of the brain. This confirms that itchy pathophysiological conditions have similar effects on functional and structural connectivity as those observed in chronic pain.