The Effect of Remote Electrical Neuromodulation (REN) on Conditioned Pain Modulation (CPM) in Migraine and Fibromyalgia

Migraine and Fibromyalgia (FM) are chronic pain disorders characterized by altered central pain processing and impaired endogenous pain inhibition. FM presents with widespread musculoskeletal pain, fatigue, sleep disturbance, and cognitive symptoms and is strongly associated with central sensitization. Migraine similarly involves dysfunction of central inhibitory and descending pain modulation, with evidence of abnormal cortical excitability, impaired sensory habituation, and alterations in pain-related evoked potentials. Conditioned Pain Modulation (CPM) is a measure of the body's endogenous pain-inhibitory mechanism, based on the phenomenon whereby the pain evoked by one painful stimulus (the test stimulus) is reduced by the concurrent application of a second, remote nociceptive stimulus (the conditioning stimulus). It is widely regarded as a proxy for the function of descending pain-modulatory pathways. CPM is used as an experimental biomarker of descending pain inhibition across chronic pain conditions, including fibromyalgia and migraine. Studies consistently demonstrate reduced inhibitory responses in both migraine and fibromyalgia compared with healthy controls, indicating a robust deficit in descending pain modulatory systems. Combining a contact heat test stimulus (TS) with a cold pressor conditioning stimulus (CS) is a widely used and validated CPM paradigm. Nerivio, a Remote Electrical Neuromodulation (REN) device, is a non-invasive, non-pharmacological therapy indicated for the acute and preventive treatment of migraine. The REN device is worn on the upper arm and delivers peripheral electrical stimulation to activate CPM-related descending inhibitory pathways and reduce migraine pain. This distal stimulation approach is designed to activate CPM-related circuits by recruiting brainstem pain-regulatory centers and modulating central nociceptive processing. This randomized, double-blind, placebo-controlled trial is designed to assess the effect of a single REN session on CPM and cortical pain processing in adults with migraine or fibromyalgia. Using a standardized CPM induction protocol, the study will evaluate changes in behavioral CPM responses, before, during, and after REN vs. sham stimulation in patients with migraine or fibromyalgia. This study aims to clarify whether REN enhances descending pain inhibition and pain processing in populations with impaired endogenous pain modulation.