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Changing Stone Composition in Recurrent Stone Formers
Kashif Alvi, MD, Mohummad M. Siddiqui, MD, Sharif-Tabrizi Ahmad, MD Stephen P. Dretler, MD, Dianne Sacco, MD.
Massachusetts General Hospital, Boston, MA, USA.

Background:
Nephrolithiasis is a recurrent condition in which approximately 50-70% of all stone formers have a risk of subsequent stone formation. Preventative treatment is based on the stone type as well as serum and urinary metabolic factors. The possibility that a recurrent stone former can make more than one stone type over time was evaluated.

Methods:
A medical record review was performed of 120 patients who had repeat stone analysis from two 2 distinct stone events between 2003 and 2008. Stone analyses were performed on stones retrieved either after ureteroscopy/laser lithotripsy, percutaneous ultrasonic lithotripsy or from voided specimens. The same laboratory analyzed all these stones.
The stones were noted to be either Calcium phosphate, Calcium oxalate monohydrate, Calcium oxalate dihydrate, Ammonium Urate, Brushite (Calcium hydrogen phosphate dihydrate), Struvite, Uric Acid, Cystine, Ammonium Urate, and Xanthine stones.

Results:

A total of 120 patients and 270 stones analysis were reviewed. Out of the analyzed stones, 71% were of mixed composition and 29% of the stones were of pure stone composition. A total of 2.5% of the patients with pure stone type in this study converted to a pure stone of an alternate composition. An additional 21.7% patient had conversion of a pure to a mixed composition stone or vice versa. Lastly, 15% had mixed stones that changed into a different mixed composition. Therefore, stone composition changed in 39% of the patients in this study upon repeat analysis. Of the patients with stones that changed, 48% of the patients had mainly calcium oxalate monohydrate stones that changed in composition over time.

Conclusion:

Stone composition may change in recurrent stone formers with subsequent stone analysis. In our study, 39% of recurrent stone formers had a change in their stone composition. In some of these cases, changes in medical management or further metabolic workup may be indicated to address the new stone composition. These findings suggest that a solitary stone analysis may not be reliable in long term management of recurrent stone formers.


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