Persistent severe pain following groin hernia repair: Somatosensory profiles, pain trajectories, and clinical outcomes - Synopsis of a PhD thesis.

Abstract

<h4>Background</h4>Persistent severe intensity pain after groin hernia repair (PSPG; 200-400/10,000 repairs) is a significant surgical complication impacting the activity of daily living (ADL) and psychosocial functioning. This PhD synopsis presents an outline and a summary of three clinical studies examining outcomes and pathophysiology behind the post-surgical pain state.<h4>Objective</h4>The studies assessed (I) treatment outcomes, i.e., re-surgery with meshectomy and selective neurectomy vs pharmacotherapy, (II) temporal trajectories of pain intensity following the primary repair, and (III) somatosensory profiles before and after re-surgery.<h4>Methods</h4>On a national basis, patients experiencing PSPG (>3 months) with an activity-related or maximal pain intensity >7 (NRS; 0-10) referred to our unit were examined. Validated questionnaires classifying NRS, ADL functions, and psychometrics, and standardized quantitative sensory testing assessing somatosensory phenotypes were used. Study I was a prospective, questionnaire-based cohort analysis comparing outcomes from a 5-year perspective. Study II retrospectively examined patient-reported pain intensity trajectories. Study III followed somatosensory outcomes before and after re-surgery.<h4>Results</h4>In Study I (responder ratio: 172/204 [84%]), patients were allocated to re-surgery (<i>n</i> = 54) or to pharmacotherapy (<i>n</i> = 118). Compared to baseline, both cohorts showed significant improvements in pain intensity and ADL functions (<i>P</i> < 0.0001), with a slight superiority in ADL functions for the re-surgical cohort (<i>P</i> = 0.02). The number needed to operate for one patient to achieve a positive outcome (≥25% change in NRS/ADL) ranged between 1.5 and 1.9, and for experiencing a negative outcome, between 14 and 28. Study II (<i>n</i> = 95) identified two main prototypes of post-surgical pain intensity trajectories, where 51% experienced undiminished pain after the primary repair, while 29% experienced normal post-surgical recovery followed by late development of PSPG. Study III (<i>n</i> = 60) indicated that re-surgery was associated with a loss in the cutaneous somatosensory function and deep mechanical nociceptive function (decrease in evoked pain sensitivity).<h4>Summary</h4>The thesis corroborates that both re-surgical intervention and pharmacotherapy may ameliorate high-intensity pain and increase ADL functions in PSPG. Since the study design cannot account for non-specific therapeutic effects, a high-quality RCT is still needed. The pathophysiologic results indicate that the implanted mesh acts as a "pain generator", and future research should be targeted at dampening the immuno-inflammatory response to the implanted mesh.