Impact of Peripheral Afferent Input on Central Neuropathic Pain

Impact of Peripheral Afferent Input on Central Neuropathic Pain

The overarching aim of this study is to investigate the contribution of peripheral afferent input to spontaneous and evoked central neuropathic pain after a spinal cord lesion or disease.

A key question that has been subject to longstanding debates in the field relates to the sites and mechanisms within the peripheral or central nervous system that potentially perpetuate chronic spontaneous and evoked central neuropathic pain. The investigators hypothesize that spontaneous central neuropathic pain depends on continuous, "physiological" somatosensory input from the painful body region in the periphery. Thus, spontaneous central neuropathic pain results from pathological gain control in central somatosensory networks with decreased activation thresholds for thermo- and mechanosensitive peripheral afferents.

Inclusion Criteria:

• Definite central neuropathic pain according to current diagnostic algorithms involving at least both feet or both hands bilaterally and symmetrically with regard to the expected neuroanatomical distribution of the nerve block.
• Patients with spinal cord injury. For patients with pain in both legs, the injury has to be incomplete. For patients with pain in both arms, the injury can be complete or incomplete. The pain in the area that will be investigated (region of interest) has to be in an area with at least some preservation of sensation
• An intensity of spontaneous pain of ≥4 NRS [0-10] in the region of interest during the screening visit and at the day of the intervention.
• Participant is able and willing to give informed consent.
• For female subjects of childbearing potential: A negative pregnancy test and either use of highly effective contraception or sexual abstinence

Exclusion Criteria:

• Conus/cauda involvement or evidence of peripheral neuropathic pain due to documented peripheral lesion.
• Other known neurological and psychiatric conditions
• History or symptoms of significant diseases that may confound the measurements or represent contra-indications for the intervention (e.g., neuropathy following cancer or metabolic diseases such as diabetes mellitus, liver diseases, and kidney diseases.
• Cardiovascular diseases that preclude the anaesthetic intervention (e.g., arrythmias).
• Concomitant nociceptive pain within the innervation territory of the planned nerve block.
• Unable to understand and speak Danish
• Changes in pain medication within the last 4 weeks prior to the intervention.
• Treatment with warfarin or other blood thinning medications, that contraindicates regional anesthesia if the treating physician cannot recommend that such treatments are paused for at least 7 days before the study day
• Infection or skin disease in planned injection area
• Allergy for local anesthetics
• Pregnancy or lactation.
• Alcohol or drug abuse
• Pain intensity below 4 in the region of interest at the baseline measurement before the nerve block