The incidence of lower-pole nephrolithiasis--increasing or not?

To determine if the incidence of lower-pole nephrolithiasis is increasing.

A previously published meta-analysis of trends in the location of stones in the kidney, using data from 1984 to 1992, determined the percentage of lower pole stones in 26,722 kidney stones treated by extracorporeal shockwave lithotripsy (ESWL). We performed prospective studies on all patients treated by ESWL for a single renal stone (not manipulated from the ureter) in two organizations: at Lithotripters Inc., 47,303 stones were treated with ESWL by 1000 urologists in private practice from 1989 to 1995. At the Midwest Urologic Stone Unit, 9357 stones were treated with ESWL by 200 urologists in private practice from 1987 to 1995. The distribution of stones in both samples was compared with that reported earlier.

The meta-analysis for stone location trends from the previously published article suggested that the percentage of kidney stones in the lower pole at ESWL increased erratically from 1984 to 1989 but was then stable for 3 years. The Lithotripters Inc. sample showed an essentially constant incidence from 28% in 1990 to 30% in 1995, and the Midwest Urologic Stone Unit sample showed an essentially constant incidence from 35% in 1988 to 36% in 1995.

The incidence of lower pole nephrolithiasis has remained stable from 1990.