Effects of the glial modulator palmitoylethanolamide on chronic pain intensity and brain function

Background: Chronic neuropathic pain (NP) is a complex disease that results from damage or presumed damage to the somatosensory nervous system. Current treatment regimens are often ineffective. The major impediment in developing effective treatments is our limited understanding of the underlying mechanisms. Preclinical evidence suggests that glial changes are crucial for the development of NP and a recent study reported oscillatory activity differences within the ascending pain pathway at frequencies similar to that of cyclic gliotransmission in NP. Furthermore, there is evidence that glial modifying medications may be effective in treating NP. The aim of this Phase I open-label clinical trial is to determine whether glial modifying medication palmitoylethanolamide (PEA) will reduce NP and whether this is associated with reductions in oscillatory activity within the pain pathway. Methods: We investigated whether 6 weeks of PEA treatment would reduce pain and infra-slow oscillatory activity within the ascending trigeminal pathway in 22 individuals (17 females) with chronic orofacial NP. Results: PEA reduced pain in 16 (73%) of the 22 subjects, 11 subjects showed pain reduction of over 20%. Whilst both the responders and non-responders showed reductions in infra-slow oscillatory activity where orofacial nociceptor afferents terminate in the brainstem, only responders displayed reductions in the thalamus. Furthermore, functional connections between the brainstem and thalamus were altered only in responders. Conclusion: PEA is effective at relieving NP. This reduction is coupled to a reduction in resting oscillations along the ascending pain pathway that are likely driven by rhythmic astrocytic gliotransmission.