"Mirror pain" as an unusual presentation of renal colic.

Although most patients suffering from pain related to upper urinary tract stones feel the discomfort on the same side as the stone, rarely it is perceived on the opposite side. We sought to identify the prevalence of this clinical scenario and to review possible explanations. The charts and x-rays of all patients with unilateral, symptomatic, radiologically identifiable upper urinary tract stones, seen at an outpatient clinic between June 1993 and August 1996, were reviewed retrospectively in terms of the side of the discomfort in comparison to the side of the stone. Three of 631 patients presented with contralateral or "mirror pain" secondary to a renal or ureteric calculus. In each case the symptoms resolved completely following successful extracorporeal shock wave lithotripsy or spontaneous passage of the stone.