Persistent sensory dysfunction in pain-free herniotomy

Persistent post-herniotomy pain may be a neuropathic pain state based on the finding of a persistent sensory dysfunction. However, detailed information on the normal distribution of sensory function in pain-free post-herniotomy patients hinders identification of exact pathogenic mechanisms. Therefore, we aimed to establish normative data on sensory function in pain-free patients >1 year after a groin herniotomy.

Sensory thresholds were assessed in 40 pain-free patients by a standardized quantitative sensory testing (QST). Secondary endpoints included comparison of sensory function between the operated and the naïve side, and correlation between sensory function modalities.

QST showed that on the operated side, thermal data were normally distributed, but mechanical pressure and pinch thresholds were normalized only after log-transformation, and cold pain and pressure tolerance could not be normalized. Comparison of QST results revealed significant (P<0.01) cutaneous hypoesthesia/hyperalgesia, but also significant pressure hyperalgesia (P<0.01) and decreased pressure tolerance (P=0.02) on the operated vs. the naïve side. Wind-up was seen in 6 (15%) but with a low pain intensity.

Persistent sensory dysfunction is common in pain-free post-herniotomy patients. Future studies of sensory function in persistent post-herniotomy pain should compare the findings to the present data in order to characterize individual patients and potentially identify subgroups, which may aid in allocation of patients to pharmacological or surgical treatment.