Somatosensory and trophic findings in the referred pain area in patients with kidney stone disease.

Background and purpose Visceral and somatic afferents activate the same neuronal structures in the central nervous system. Assessing somatosensory function and trophic changes in the referred pain area may therefore indirectly increase information on mechanisms involved in painful visceral diseases. The aim of this study was to evaluate the sensory and trophic changes in the flank corresponding to the referred pain area in patients with kidney stone disease. Methods A total of 24 patients with unilateral pain-causing kidney stone disease were studied before and after endoscopic percutaneous kidney stone surgery. Trophic changes and sensitivity on the affected and on the contra-lateral side in the pain free period were investigated. For this purpose we used standardized experimental sensory testing including pressure stimulation and electrical (single and repeated) skin stimulation. Five repeated stimuli were used to investigate temporal summation (increased responses to repeated stimuli). To investigate trophic changes ultrasound as well as CT-scan was used, since the latter is considered more precise for exact tissue layer measurements. Results The pain tolerance thresholds to pressure and pain thresholds to electrical stimulation were not significantly different on the two sides (all P>0.1). After surgery no significant alterations in sensitivity were detected, but there was a tendency to higher pain thresholds to electrical stimuli on the affected side (single stimuli P=0.06; repeated stimuli P=0.09). No trophic changes were observed (all P>0.3), and there were no relations between the pain thresholds or trophic findings and the number of colics (all P >0.08). Conclusion In patients with unilateral pain-causing kidney stone disease the pain to experimental pressure and electrical stimuli were comparable on the affected and contra-lateral side. For the first time a CT-scan was used to evaluate tissue thickness in the referred pain area. No trophic changes were seen in the muscle or subcutaneous tissue at the affected side, and there were no correlations between the pain thresholds or trophic findings and the patients history of number of colics. After the operation no significant alterations in sensitivity were detected. Implications This study could not confirm previous studies showing referred hyperalgesia in the skin and trophic changes in the referred pain area to painful visceral disease. Differences in the pain intensity/duration between different diseases and hence the corresponding central neuronal changes may explain the negative findings in the present study.