Quantitative validation of sensory mapping in persistent postherniorrhaphy inguinal pain patients undergoing triple neurectomy.

PURPOSE: Neurectomy of the inguinal nerves may be considered for selected refractory cases of chronic postherniorrhaphy inguinal pain (CPIP). There is to date a paucity of easily applicable clinical tools to identify neuropathic pain and examine the neurosensory effects of remedial surgery. The present quantitative sensory testing (QST) pilot study evaluates a sensory mapping technique.

METHODS: Longitudinal (preoperative, immediate postoperative, and late postoperative) dermatomal sensory mapping and a comprehensive QST protocol were conducted in CPIP patients with unilateral, predominantly neuropathic inguinodynia presenting for triple neurectomy (n = 13). QST was conducted in four areas on the affected, painful side and in one contralateral comparison site. QST variables were compared according to sensory mapping outcomes: (o)/normal sensation, (+)/pain, and (-)/numbness. Diagnostic ability of the sensory mapping outcomes to detect QST-assessed allodynia or hypoesthesia was estimated through calculation of specificity and sensitivity values.

RESULTS: Preoperatively, patients exhibited mechanical hypoesthesia and allodynia and pressure allodynia and hyperalgesia in painful areas mapped (+) (p < .05); sensory mapping outcome (+) demonstrated high ability to detect mechanical allodynia [sensitivity 0.74 (95% CI 0.61-0.86), specificity 0.94 (0.84-1.00)] and pressure allodynia [sensitivity 0.96 (0.89-1.00), specificity 1.00 (1.00-1.00)], but not thermal allodynia. Postoperatively, mapped areas of numbness (-) were associated with mechanical and thermal hypoesthesia (p < .05); (-) showed high sensitivity and specificity to detect mechanical and cold hypoesthesia.

CONCLUSIONS: Sensory mapping provides an accurate clinical neuropathic assessment with strong correlation to QST findings of preoperative mechanical and pressure allodynia, and postoperative mechanical and thermal hypoesthesia in CPIP patients undergoing neurectomy.