STONE DISEASE

Renal Stone Epidemiology in Rochester, Minnesota: An Update
Lieske JC, Pena de la Vega LS, Slezak JM, Bergstralh EJ, Leibson CL, Ho KL, Gettman MT
Department of Internal Medicine, Division of Nephrology and Hypertension, Mayo Clinic, Rochester, Minnesota, USA
Kidney Int. 2006; 69: 760-4

• Studies in Western countries have suggested an increasing incidence of nephrolithiasis (NL) in the latter part of the 20th century. Therefore, we updated NL epidemiology data for the Rochester population over the years 1970-2000. All Rochester residents with any diagnostic code that could be linked to NL in the years of 1970, 1980, 1990, and 2000 were identified, and the records reviewed to determine if they met the criteria for a symptomatic kidney stone as defined in a previous Rochester, MN study. Age-adjusted incidence (+/-s.e.) of new onset symptomatic stone disease for men was 155.1 (+/-28.5) and 105.0 (+/-16.8) per 100,000 per year in 1970 and 2000, respectively. For women, the corresponding rates were 43.2 (+/-14.0) and 68.4 (+/-12.3) per 100,000 per year, respectively. On average, rates for women increased by about 1.9% per year (P=0.064), whereas rates for men declined by 1.7% per year (P=0.019). The overall man to woman ratio decreased from 3.1 to 1.3 during the 30 years (P=0.006). Incident stone rates were highest for men aged 60-69 years, whereas for women, they plateaued after age 30. Therefore, since 1970 overall NL incidence rates in Rochester have remained relatively flat. However, NL rates for men have declined, whereas rates for women appear to be increasing. The reasons remain to be determined.
  
  
• Editorial Comment
  Though most recent studies suggest an increase in the incidence of nephrolithiasis, attributed to dietary and lifestyle changes, this interesting study suggests the contrary. An increase in incidence in females is balanced by a decrease in incidence in males, leading to a flat incidence rate when compared to 30 years ago.
  The authors note that affluence and dietary factors associated with higher socioeconomic status have been implicated as risk factors for stone disease. It would be important therefore to evaluate any changes in the socioeconomic status of their study group; for example has the average income, unemployment rate, average education etc. remained stable during this time period? The intriguing question remains what has changed in men from 1980 onwards that has dramatically decreased the incidence of stone disease? What has changed in women from 1970 onwards that has resulted in a dramatic increase in stone disease? Is it dietary, hormonal, environmental, iatrogenic (increased use of oral contraceptives, calcium supplements, or other agents)? The authors reported only the incidence of symptomatic stones, though they did extract all stones including those detected incidentally by high-resolution imaging technologies. It would be interesting for the investigators to report these numbers also, so as to predict the increased volume of patients being referred for prophylactic surgical and medical therapy.

Dr. Manoj Monga
Professor, Department of Urology
University of Minnesota
Edina, Minnesota, USA