• E K Aasvang, M U Werner, and H Kehlet.
• Section for Surgical Pathophysiology, Copenhagen University, Rigshospitalet, Copenhagen, Denmark eske.aas@gmail.com.
• Br J Anaesth. 2015 Aug 1;115(2):294-301.

BackgroundPersistent postherniotomy pain is located around the scar and external inguinal ring and is often described as deep rather than cutaneous, with frequent complaints of pain in adjacent areas. Whether this pain is due to local pathology or referred/projected pain is unknown, hindering mechanism-based treatment.MethodsDeep tissue electrical pain stimulation by needle electrodes in the right groin (rectus muscle, ilioinguinal/iliohypogastric nerve and perispermatic cord) was combined with assessment of referred/projected pain and the cutaneous heat pain threshold (HPT) at three prespecified areas (both groins and the lower right arm) in 19 healthy subjects. The assessment was repeated 10 days later to assess the reproducibility of individual responses.ResultsDeep electrical stimulation elicited pain at the stimulation site in all subjects, and in 15 subjects, pain from areas outside the stimulation area was reported, with 90-100% having the same response on both days, depending on the location. Deep pain stimulation significantly increased the cutaneous HPT (P<0.014). Individual HPT responses before and during deep electrical pain stimulation were significantly correlated (ρ>0.474, P≤0.040) at the two test days for the majority of test areas.ConclusionOur results corroborate a systematic relationship between deep pain and changes in cutaneous nociception. The individual referred/projected pain patterns and cutaneous responses are variable, but reproducible, supporting individual differences in anatomy and sensory processing. Future studies investigating the responses to deep tissue electrical stimulation in persistent postherniotomy pain patients may advance our understanding of underlying pathophysiological mechanisms and strategies for treatment and prevention.Trial Registry NumbersClinicalTrials.gov (NCT01701427).© The Author 2015. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

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