Somatosensory changes in the referred pain area following acute inflammation of the appendix

Abdominal pain provoked by acute gastrointestinal disease may increase the sensitivity in the referred somatic pain area. The aim of this study was to examine sensory changes in the referred pain area during acute appendicitis.

Twenty patients with clinical symptoms of appendicitis were included; 16 of these had appendicitis confirmed at operation. Ten healthy volunteers served as controls.

In patients with symptoms of appendicitis, somatic sensitivity was assessed using different stimuli presented in the area of referred pain and in a comparable non-painful area at the contralateral site of the abdomen. In healthy control subjects, the same stimuli were presented to McBurney's point and at a similar area on the left abdomen. The rating to pinprick was determined using a Von Frey hair. The rating to thermal stimuli was tested by warm and cold metal rollers. A constant current stimulator was used to measure the sensation and pain-detection threshold to single and repeated electrical stimuli. The pressure pain threshold was determined by an electronic pressure algometer.

Patients (n = 16) with verified appendicitis showed increased ratings to pinprick (50%, P < 0.05) and thermal stimuli (56%, P < 0.05) in the referred pain area. There was a reduction in pain thresholds to single electrical (4.3 v. 8.4 mA, P = 0.001), repeated electrical (3.5 v. 4.6 mA, P = 0.005) and pressure (89 v. 243 kPa, P < 0.001) stimuli in the referred pain area versus the control area. In the control group, no difference was observed between the two areas. The pain thresholds for electrical and pressure stimuli were lower in the referred pain area in patients compared with the same area in controls (P < 0.001).

Somatosensory hyperalgesia to experimental stimuli was observed in acute appendicitis. We believe that viscerosomatic convergence mechanisms and central nervous system hyperexcitability explain these findings.