[Epidemiological characteristics of urolithiasis in Okhotsk coast area in Hokkaido]

An epidemiological study of 422 stone-formers who visited our hospital from 1997 to 2001 was conducted. The mean annual prevalence and incidence of both upper and lower urinary tract stones were higher than what was found in a nationwide urolithiasis survey carried out in Japan in 1995. The incidence of upper and lower urinary tract stones was 90.8% and 9.2%, respectively. The frequency of lower urinary tract stones was higher than that found in the previously mentioned nationwide study. The male-to-female ratio of upper and lower urinary tract stones was 1.68:1 and 2.25:1, respectively. The frequency in females was higher in this study than that found in the nationwide survey. The peak age for incidence of upper urinary tract stones is 50s in males and females. In the treatment of upper urinary tract stones, ureteroscopic lithotripsy was carried out more often than shock wave lithotripsy (SWL), because our hospital had no SWL device. Many endoscopic lithotripsy procedures were performed to treat stones located in the lower urinary tract. Of the upper urinary tract stones 83.7% were composed of calcium, the incidence of uric acid stones was high (6.6%), whereas the incidence of infectious stones was low (1.9%). For lower urinary tract stones, the frequency of infectious stones was high (52.6%). In the present study, the epidemiological features were as follows: high annual prevalence and incidence, high frequency of lower urinary tract stones, high frequency in females, many endoscopic treatment procedures and high frequency of uric acid stones in the upper urinary tract.