Characterization of Electroencephalographic (EEG) Signatures of Chronic Pain Patients Receiving Intravenous Ketamine.

The prevalence of chronic pain in the general population varies between 10 and 52% depending on the study, 7% of which is neuropathic pain. These neuropathic pains have various origins: post-surgical, post-herpetic, post-traumatic, etc. These chronic pain symptoms can lead to sleep and mood disorders, restrict domestic and work activities and have a significant impact on quality of life.

Anxiety-depression comorbidities are found in a large number of patients, with harmful consequences on pain since they aggravate symptoms and their repercussions. Conversely, pain increases psychological distress.

Ketamine, derived from phencyclidine, is an anesthetic agent used since the 1960s. It acts by non-competitive antagonism of the N-methyl-D-aspartate (NMDA) receptors found mainly in the hippocampus and prefrontal cortex. This receptor is one of the binding sites for glutamate, an excitatory neurotransmitter involved in the transmission of painful messages, long-term memory processes, and hyperalgesia. Ketamine has been used in the context of depressive episodes characterized by its rapid action. It is also increasingly used in chronic pain due to its regulating action on the "wind up" effect, a phenomenon involved in the central hypersensitization that is inevitably present in neuropathic pain with a prolonged course. The mechanisms underlying the improvement of neuropathic pain after ketamine infusion are not fully elucidated. Some animal studies suggest a prolonged anti-aversive effect on the anterior cingulate cortex or a weaker connectivity between the prefrontal cortex and the precuneus in patients who respond to ketamine. At the same time, the antidepressant effect seems to be linked to an action on the prefrontal cortex. Overall, the literature shows a strong association between anxiety-depressive symptoms and chronic pain.

EEG recording of patients with neuropathic pain before and during ketamine infusion would allow the acquisition of important electro-physiological data.

Several studies have found that EEG signatures was associated with a good antidepressant response to Ketamine. The frequency, absolute and relative power and cordance of the EEG signal in certain frequency ranges (theta, alpha, beta and gamma) could be useful for guiding and adapting therapies for depression as well as pain.