Re: Multiple myeloma presenting as acute tubulointerstitial nephritis and normal serum protein electrophoresis.

318 Iranian Journal of Kidney Diseases | Volume 6 | Number 4 | July 2012 kidney calculi, the clinical features and risk factors of urolithiasis were evaluated.1 They concluded that urolithiasis remains a serious problem in Iranian children. In addition, family history of urolithiasis, urologic abnormalities, metabolic disorders, and urinary tract infections were associated risk factors for pediatric urolithiasis.1 We agree that the wide geographic variations in pediatric urolithiasis exist in terms of the incidence of lithiasis in childhood, site of formation, stone composition, and predisposing etiological factors. Authors noted that the stones were only located in 90.6% of the cases in the upper urinary tract and in 2.4% it was only in the bladder1; however, in a Tunisian study on 300 children with urolithiasis, the calculi were located in the kidneys in 69.0% of patients and bladder stones were observed in 27.7% of cases.2 Importantly, bladder stones have been reported to be endemic in Asia such as Tunisia.2 Infants appear to be more affected by bladder stones than teenagers (42.4% versus 16.1%, P < .001).2 Family history of renal stones was noted in 8% of Tunisian cases,2 while it was reported in 27% of Iranian pediatric patients.1 A history of urinary tract infection was the same in the both studies, approximately 25% of individuals.1,2 Metabolic disorders were reported in 53% of Iranian pediatric with urinary calculi,1 while it was noted in 9% of Tunisian patients.2 In both studies, urolithiasis was more likely to be occurred in boys than girls, and the male-female ratio was 1.4:1 in Iranian cases and 1.54:1 in Tunisian subjects.1,2 Furthermore, in most studies male predominance was observed among pediatric urolithiasis.3,4 The urological abnormalities in Iranian children was also similar to Tunisian patients (14% versus 11%),1,2 which matches with other studies.5,6