Application of local anesthesia inhibits effects of low-energy extracorporeal shock wave treatment (ESWT) on nociceptors.

OBJECTIVE

Clinical studies of extracorporeal shock wave therapy (ESWT) provided conflicting results depending on the use of local anesthesia (LA).

DESIGN

The present study investigated whether the biological effects of ESWT differ between application with and without LA.

SETTING AND PATIENTS: In 20 healthy subjects, ESWT was applied to the ventral surface of forearm skin, either after topical lidocaine pretreatment or without on the corresponding contralateral side.

MEASURES: During and after ESWT ongoing pain, axon-reflex vasodilation (laser Doppler imaging), thresholds for pinprick, and blunt pressure were recorded.

RESULTS

The results indicate that increasing ESWT energy flux density led to increasing pain (P < 0.001). LA reduced ESWT-related pain (P < 0.02) and in parallel inhibited local axon-reflex vasodilation (P < 0.001). In addition, LA prevented ESWT-related drop in pressure pain threshold (P < 0.001).

CONCLUSION

This study provided evidence that ESWT dose-dependently activates and sensitizes primary afferent nociceptive C-fibers, and that both activation and sensitization were prevented if LA was applied locally. These results suggest that LA substantially alters the biological responses of ESWT.