Previous studies suggested that patients with pure struvite calculi rarely have underlying metabolic abnormalities. Therefore, most of these patients do not undergo metabolic studies. We report our experience with these patients and their response to directed medical therapy. Between 1/2005 and 9/2012, 75 patients treated with percutaneous nephrolithotomy for struvite stones were identified. Of these, 7 had pure struvite stones (Group 1), 32 had mixed struvite stones (Group 2), both with metabolic evaluation, and 17 had pure struvite stones without metabolic evaluation (Group 3). The frequency of metabolic abnormalities and stone activity (defined as stone growth or stone-related events) was compared between groups. The median age was 55 years and 64 % were female. No significant difference in race, infection history, family history, stone location or volume existed between groups. Metabolic abnormalities were found in 57 % of Group 1 and 81 % of Group 2 patients. A similar proportion of Group 1 and 2 patients received modification to or continuation of metabolic therapy, whereas no Group 3 patients received any directed therapy. In patients with >6 months follow-up, the stone activity rate between Groups 1 and 2 appeared similar whereas Group 3 trended towards higher stone activity rate. Metabolic abnormalities in pure struvite stone formers appear to be more common than previously reported. Directed medical therapy in these patients may reduce stone activity. The role of metabolic evaluation and directed medical therapy needs reconsideration in patients with pure struvite stones.
Keywords: Nephrolithiasis; Recurrence; Struvite; Treatment outcome.