Retrospective Follow-Up of Patients with Struvite Calculi

Abstract

The cause and effect relationship of urinary infection and urinary calculi is an ancient concept. Contemporary clinical and experimental investigations support the traditional belief that infection-induced calculi result primarily as a consequence of the hydrolysis of urea by the bacterial enzyme urease¹. The accumulated information supports the widespread clinical experience that infection induces the formation of struvite and carbonate apatite calculi. The exact incidence of infection-induced calculi is unknown. Available data is collected largely from reference laboratories that analyze many calculi. Such data indicates that the incidence of struvite calculi is up to 20% of calculi analyzed². This may be a falsely elevated figure, because most struvite calculi are removed surgically and sent for analysis whereas a high percentage of other types of stones, such as calcium oxalate, are passed spontaneously and may not be recovered by the patient or sent by the physician for analysis. Struvite stones comprise approximately 15% of the calculi analyzed at the Baylor-affiliated Urolithiasis Laboratory. Since 1973, 2066 struvite calculi have been analyzed. A questionnaire was devised to evaluate the clinical course of these patients retrospectively. These questionnaires were sent to the attending physician for completion. An attempt was made to design a form that could be filled out easily and quickly in order to obtain a good response rate. The main objectives of the study were to evaluate the incidence of recurrent infection, recurrent calculi, and the types of procedures performed for removing calculi. The format was constructed in such a manner that the information obtained could be easily electronically processed for tabulation and analysis. Approximately 600 questionnaires were returned, and of these 527 were adequate for analysis. Ninety-two percent of the stones were removed surgically. Follow-up ranged from 5-74 months with a mean of 14.5 months.