Background Central sensitization (CS) is a common phenomenon among patients with knee osteoarthritis. In a previous study, our team showed that CS occurs gradually, and no dummy, and has an important role in the development of chronic pain. Neuroimaging is a procedure that allows us to objectify the pain assessment. The study of the resting state help us to detect alterations in brain function at rest.
Objectives The aim of this study is to identify the subgroup of patients sensitized and to characterize their changes in functional connectivity with functional Magnetic Resonance Imaging (fMRI).
Methods This is a cross-sectional, single blind (investigator) study of 60 patients with knee osteoarthritis. Presence of CS was assessed using extended version of the Arendt-Nielsen peripatellar map, following the evidence of regional spread of pain and, also, temporal summation which is increased pain response to repeated stimulation. FMRI included two resting sequences in which the subject had to remain lying down and stay as relaxed as possible and let flow the mind. These sequences were interspersed with another sequence in which painful stimulation of the medial interline was applied in order to observe changes in functional connectivity before and after a similar pain caused by the disease itself.
Results A total of 33 patients showed some degree of CS of which 19 of them met all the established criteria. In the analysis of the resting state sequence before painful stimulation, no significant differences between sensitized and non sensitized patients were found. However, the results of resting state sequence after pain stimulation showed a significant heightened functional connectivity, especially in the posterior insula. When the somatosensory cortex (SII) was selected as a region of interest, we found enhanced functional connectivity, in resting state sequence before pain, with the anterior insula and also, a reduction of functional connectivity with the anterior cingulate cortex was identified. In the resting state sequence after pain stimulation, a similar pattern was revealed with increased intensity.
Conclusions It is widely known that SII is associated to the information processing coming from the leg and insula, which is related to information integration and visceral sensation or interoception. The increased connectivity found between both SII and insula, after painful stimulation stopped, could show that sensitized patients experience pain even when the initial stimulation has disappeared, such a fingerprint.
These results, together with those previously obtained in the sequences of painful stimulation, help to get an overall picture of these patients. This study is a starting point to investigate new therapeutic approaches to expand the current management of these patients and improve their quality of life.
Disclosure of Interest None declared