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Re: the Association of Increasing Body Mass Index and Kidney Stone Disease
1984
LETTERS TO THE EDITOR/ERRATA
We have suggested a simple method that can help investigators and their readers assess the potential impact of 2 issues that commonly plague prospective cohort studies. Respectfully, Alexander S. Parker Department of Urology Mayo Clinic Jacksonville Jacksonville, Florida 1. Friis RH and Sellers TA: Study designs: cohort studies. In: Epidemiology for Public Health Practice, 3rd ed. Sudbury, Massachusetts: Jones and Bartlett 2003; pp 253–287.
Re: the Association of Increasing Body Mass Index and Kidney Stone Disease M. J. Semins, A. D. Shore, M. A. Makary, T. Magnuson, R. Johns and B. R. Matlaga J Urol 2010; 183: 571–575.
To the Editor: We congratulate the authors on their study associating obesity, ie body mass index (BMI) greater than 30 kg/m2, with an increased risk of kidney stone disease. What is more, the magnitude of this risk appears to be stable in the morbidly obese population. However, we found that some questions remain. First, this study only showed mean age in patients with stones, without evaluating the BMI of different age groups. Actually the incidence of stone disease varies by age. For men the incidence begins to increase after age 20, peaks between 40 and 60, and then begins to decrease.1–3 For women the incidence begins to increase after age 20, and then decreases after age 50.3,4 The authors also did not offer information about patient race. It is clear that racial background would interfere with the outcome of this study because it would affect not only the incidence of stones, but also BMI values. Some studies have revealed that stone disease when categorized by racial background is most prevalent among older white males and lowest in younger black individuals, with Asians falling somewhere in between.5–7 Additionally body weight fluctuates throughout life, as does BMI, and so weight gain should have an important role in the formation of stones. Therefore, all stone formers need followup at regular intervals to investigate weight fluctuation. Although BMI is a risk factor for kidney stone formation, the article did not state whether the risk for females and males is equal. However, epidemiological studies have disclosed that the male-to-female ratio of stone disease is 3:1 to 4:1.8 Thus, the authors need to disclose whether BMI is a higher risk for male or female stone formers. Respectfully, Jiang Jun Yi, Li Jin Yi, Gao Zhi Xiang, Wang Wu Qing, Liu Ji Yong and Liu Jun Jiang Department of Urology Changhai Hospital Second Military Medical University Shanghai, China 1. Johnson CM, Wilson DM, O’Fallon WM et al: Renal stone epidemiology: a 25-year study in Rochester, Minnesota. Kidney Int 1979; 16: 624.
5. Stamatelou KK, Francis ME, Jones CA et al: Time trends in reported prevalence of kidney stones in the United States: 1976 –1994. Kidney Int 2003; 63: 1817.
2. Curhan GC, Willett WC, Rimm EB et al: A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993; 328: 833.
6. Soucie JM, Thun MJ, Coates RJ et al: Demographic and geographic variability of kidney stones in the United States. Kidney Int 1994; 46: 893.
3. Hiatt RA, Dales LG, Friedman GD et al: Frequency of urolithiasis in a prepaid medical care program. Am J Epidemiol 1982; 115: 255.
7. Chan SW, Ng CF, Man CW et al: A report on a randomly sampled questionnaire survey about renal stone disease in Hong Kong. Hong Kong Med J 2008; 14: 427.
4. Curhan GC, Willett WC, Knight EL et al: Dietary factors and the risk of incident kidney stones in younger women: Nurses’ Health Study II. Arch Intern Med 2004; 164: 885.
8. Curhan GC: Epidemiology of stone disease. Urol Clin North Am 2007; 34: 287.
LETTERS TO THE EDITOR/ERRATA
Reply by Authors: We appreciate the comments of Yi et al. As they note, we did not subcategorize BMI cohorts by age, but rather reported only mean values. However, we noted in the results section that in our study population the likelihood of being diagnosed with a stone increased with age, from an odds ratio of 1.44 for patients 35 to 44 years to 2.44 for those 55 to 64 years old. However, as we also noted, analysis with logistic regression did not demonstrate any significant effect of age on our findings. Unfortunately racial demographics were not completely recorded in our analytical data set, so we did not subject our findings to such an analysis. As Yi et al note, the effect of race on stone risk is unresolved, so future efforts on this subject would be welcome. Although the effect of BMI change on stone risk may be important, our study was of a cross-sectional design, where the BMI value investigated corresponded to time of stone event. BMI values were not consistently recorded at regular intervals in this data set, thus precluding a formal analysis of longitudinal changes in BMI and stone risk. Finally, Yi et al ask about the effect of gender on stone risk. We note in the results section that the likelihood of being diagnosed with a stone in our study population was twice as high for men as for women. In addition, the data in table 1 in the article are separated by gender, and there are separate analyses presented for both cohorts.
Re: Urethroplasty With Abdominal Skin Grafts for Long Segment Urethral Strictures J. J. Meeks, B. A. Erickson, P. Fetchev, S. E. Crawford, N. A. Fine and C. M. Gonzalez J Urol 2010: 183; 1880 –1884.
To the Editor: This controversial study drew my attention. I have serious concerns about the flawed message that this article and its associated editorial comment appear to be sending out, ie that it is safe to repair lichen sclerosus (LS) urethral strictures with nongenital skin grafts. This small study of 21 patients mixes LS disease strictures with mechanical strictures of other etiologies. The authors, and indeed the editorial comment, fail to acknowledge that these 2 categories of stricture behave differently and require a different approach to their management. Alas, the article does not separate out the incidence of stricture recurrence within the LS group. The overall quoted recurrence rate is in any case likely to be a significant underestimate, given that the development of voiding difficulties was the criterion for further assessment, and it is well known that symptoms might not present until there is advanced narrowing of the urethral lumen. The mean followup period is just more than 2 years and includes patients with as little as 11 months of followup. Such short-term followup may allow worthwhile prediction of the outcome for mechanical stricture repair. However, it is of little value in predicting LS stricture recurrence after substitution with nongenital skin. The reported satisfactory short-term outcomes, without appropriate qualification, are misleading for the readers. My experience of 25 years in treating about 1,500 patients with genital LS and repairing hundreds of LS strictures has conclusively shown me that while dilations, urethrotomies and augmentations or substitutions with genital skin usually lead to clinical recurrence within a couple of years, nongenital skin often lasts considerably longer and, therefore, may instill false hope in doctor and patient alike. For patients with aggressively behaving LS even nongenital skin can restricture within the first year or so. However, many patients have lower grade, more insidious forms of the disease, in which restrictures develop slowly spanning the course of many years. I wish that the authors were indeed reporting a satisfactory solution for LS strictures, because inserting skin grafts is technically a much easier option than resorting to bladder mucosa substitution once available oral mucosa has been used up. I, too, thought that I had hit on the solution when I started using full thickness nongenital skin graft substitution (from various donor sites) in the mid 1980s and the early 1990s. Short-term results for the first couple of years
1985
LETTERS TO THE EDITOR/ERRATA
We have suggested a simple method that can help investigators and their readers assess the potential impact of 2 issues that commonly plague prospective cohort studies. Respectfully, Alexander S. Parker Department of Urology Mayo Clinic Jacksonville Jacksonville, Florida 1. Friis RH and Sellers TA: Study designs: cohort studies. In: Epidemiology for Public Health Practice, 3rd ed. Sudbury, Massachusetts: Jones and Bartlett 2003; pp 253–287.
Re: the Association of Increasing Body Mass Index and Kidney Stone Disease M. J. Semins, A. D. Shore, M. A. Makary, T. Magnuson, R. Johns and B. R. Matlaga J Urol 2010; 183: 571–575.
To the Editor: We congratulate the authors on their study associating obesity, ie body mass index (BMI) greater than 30 kg/m2, with an increased risk of kidney stone disease. What is more, the magnitude of this risk appears to be stable in the morbidly obese population. However, we found that some questions remain. First, this study only showed mean age in patients with stones, without evaluating the BMI of different age groups. Actually the incidence of stone disease varies by age. For men the incidence begins to increase after age 20, peaks between 40 and 60, and then begins to decrease.1–3 For women the incidence begins to increase after age 20, and then decreases after age 50.3,4 The authors also did not offer information about patient race. It is clear that racial background would interfere with the outcome of this study because it would affect not only the incidence of stones, but also BMI values. Some studies have revealed that stone disease when categorized by racial background is most prevalent among older white males and lowest in younger black individuals, with Asians falling somewhere in between.5–7 Additionally body weight fluctuates throughout life, as does BMI, and so weight gain should have an important role in the formation of stones. Therefore, all stone formers need followup at regular intervals to investigate weight fluctuation. Although BMI is a risk factor for kidney stone formation, the article did not state whether the risk for females and males is equal. However, epidemiological studies have disclosed that the male-to-female ratio of stone disease is 3:1 to 4:1.8 Thus, the authors need to disclose whether BMI is a higher risk for male or female stone formers. Respectfully, Jiang Jun Yi, Li Jin Yi, Gao Zhi Xiang, Wang Wu Qing, Liu Ji Yong and Liu Jun Jiang Department of Urology Changhai Hospital Second Military Medical University Shanghai, China 1. Johnson CM, Wilson DM, O’Fallon WM et al: Renal stone epidemiology: a 25-year study in Rochester, Minnesota. Kidney Int 1979; 16: 624.
5. Stamatelou KK, Francis ME, Jones CA et al: Time trends in reported prevalence of kidney stones in the United States: 1976 –1994. Kidney Int 2003; 63: 1817.
2. Curhan GC, Willett WC, Rimm EB et al: A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993; 328: 833.
6. Soucie JM, Thun MJ, Coates RJ et al: Demographic and geographic variability of kidney stones in the United States. Kidney Int 1994; 46: 893.
3. Hiatt RA, Dales LG, Friedman GD et al: Frequency of urolithiasis in a prepaid medical care program. Am J Epidemiol 1982; 115: 255.
7. Chan SW, Ng CF, Man CW et al: A report on a randomly sampled questionnaire survey about renal stone disease in Hong Kong. Hong Kong Med J 2008; 14: 427.
4. Curhan GC, Willett WC, Knight EL et al: Dietary factors and the risk of incident kidney stones in younger women: Nurses’ Health Study II. Arch Intern Med 2004; 164: 885.
8. Curhan GC: Epidemiology of stone disease. Urol Clin North Am 2007; 34: 287.
LETTERS TO THE EDITOR/ERRATA
Reply by Authors: We appreciate the comments of Yi et al. As they note, we did not subcategorize BMI cohorts by age, but rather reported only mean values. However, we noted in the results section that in our study population the likelihood of being diagnosed with a stone increased with age, from an odds ratio of 1.44 for patients 35 to 44 years to 2.44 for those 55 to 64 years old. However, as we also noted, analysis with logistic regression did not demonstrate any significant effect of age on our findings. Unfortunately racial demographics were not completely recorded in our analytical data set, so we did not subject our findings to such an analysis. As Yi et al note, the effect of race on stone risk is unresolved, so future efforts on this subject would be welcome. Although the effect of BMI change on stone risk may be important, our study was of a cross-sectional design, where the BMI value investigated corresponded to time of stone event. BMI values were not consistently recorded at regular intervals in this data set, thus precluding a formal analysis of longitudinal changes in BMI and stone risk. Finally, Yi et al ask about the effect of gender on stone risk. We note in the results section that the likelihood of being diagnosed with a stone in our study population was twice as high for men as for women. In addition, the data in table 1 in the article are separated by gender, and there are separate analyses presented for both cohorts.
Re: Urethroplasty With Abdominal Skin Grafts for Long Segment Urethral Strictures J. J. Meeks, B. A. Erickson, P. Fetchev, S. E. Crawford, N. A. Fine and C. M. Gonzalez J Urol 2010: 183; 1880 –1884.
To the Editor: This controversial study drew my attention. I have serious concerns about the flawed message that this article and its associated editorial comment appear to be sending out, ie that it is safe to repair lichen sclerosus (LS) urethral strictures with nongenital skin grafts. This small study of 21 patients mixes LS disease strictures with mechanical strictures of other etiologies. The authors, and indeed the editorial comment, fail to acknowledge that these 2 categories of stricture behave differently and require a different approach to their management. Alas, the article does not separate out the incidence of stricture recurrence within the LS group. The overall quoted recurrence rate is in any case likely to be a significant underestimate, given that the development of voiding difficulties was the criterion for further assessment, and it is well known that symptoms might not present until there is advanced narrowing of the urethral lumen. The mean followup period is just more than 2 years and includes patients with as little as 11 months of followup. Such short-term followup may allow worthwhile prediction of the outcome for mechanical stricture repair. However, it is of little value in predicting LS stricture recurrence after substitution with nongenital skin. The reported satisfactory short-term outcomes, without appropriate qualification, are misleading for the readers. My experience of 25 years in treating about 1,500 patients with genital LS and repairing hundreds of LS strictures has conclusively shown me that while dilations, urethrotomies and augmentations or substitutions with genital skin usually lead to clinical recurrence within a couple of years, nongenital skin often lasts considerably longer and, therefore, may instill false hope in doctor and patient alike. For patients with aggressively behaving LS even nongenital skin can restricture within the first year or so. However, many patients have lower grade, more insidious forms of the disease, in which restrictures develop slowly spanning the course of many years. I wish that the authors were indeed reporting a satisfactory solution for LS strictures, because inserting skin grafts is technically a much easier option than resorting to bladder mucosa substitution once available oral mucosa has been used up. I, too, thought that I had hit on the solution when I started using full thickness nongenital skin graft substitution (from various donor sites) in the mid 1980s and the early 1990s. Short-term results for the first couple of years
1985