Journey of a cystinuric patient with a long-term follow-up from a medical stone clinic: necessity to be SaFER (stone and fragments entirely removed)

Abstract

There is a lack of studies looking at the longitudinal follow-up of patients with cystine stones. We wanted to assess the journey of cystinuric patients through our specialist metabolic stone clinic to improve the understanding of episodes, interventions and current outcomes in this patient cohort. After ethical approval, all patients who attended our metabolic stone clinic from 1994 to 2014 with at least one cystine stone episode were included in our study. Data were retrospectively analysed for patient demographics, stone episodes or intervention, clinical parameters and patient compliance. Over a period of 21 years, 16 patients with a median age of 15.5 years underwent a mean follow-up of 8.6 years (1-21 years). The mean number of surgical interventions was 3.1 (1-8/patient), but patients who were stone free after their first treatment had lower recurrences (p = 0.91) and lower number of interventions during their follow-up (2.7/patient, compared to those who were not stone free at 4/patient). During their follow-up period, patients with < 3 interventions had a significantly better renal function than those with ≥ 3 surgical interventions (p = 0.04). Additionally, linear regression analysis showed that eGFR was demonstrated to decline with increasing numbers of stone episodes (r 2 = 0.169). It was also noted that patients who began early medical management remained stone free during follow-up compared to those who had medical management after ≥ 2 stone episodes, of whom all had a recurrent episode. Our long-term longitudinal study of cystine stone formers highlights that patients who are stone free and receive early metabolic stone screening and medical management after their initial presentation have the lowest recurrence rates and tend to preserve their renal function. Hence, prompt referral for metabolic assessment, and the stone and fragments entirely removed (SaFER) principles are key to preventing stone episodes and improving long-term function.

Cystinuria: clinical practice recommendation

“…Surgical management of cystine renal stones does not differ significantly from other stone compositions [51][52][53] . However, due to frequent recurrent episodes, complete stone clearance is of importance where possible to avoid growth of residual fragments which may result in symptoms or further surgery later 54 . Small renal stones may be observed with periodic evaluation as they may pass.…”

Intervention strategies for cystinuria: A systematic review

“…24 Stone free rates ranged from 22 to 87% with diuresis, alkalization and pharmacological management after single or multiple surgical procedures. 11, 17, 19, 25, 27, 29, 30, 32 Thiol-treated patients had decreased stone recurrence when urinary cystine excretion was maintained at <797 mg/gm creatinine/24 hours. 25…”

“…10, 11, 17-20, 23-34 20 studies reported outcomes from surgical interventions in cystinuria patients. 10, 11, 17-20, 24-26, 29, 30, 32-40 Of the 24 studies, 15 reported combined intervention methods with alkalinizing compounds, pharmacological drugs and/or surgical procedures. 10, 11, 17-20, 24-27, 29, 30, 32-34 No studies directly compared pharmacological intervention to surgical intervention.…”

“…10, 17-20, 23-28, 31, 32, 34-38, 40 Of the 24 studies, 5 reported median patient age, which ranged from 6 to 18.5 years. 11, 29, 30, 33, 39…”

“…18 Of the 24 studies, 16 reported the use of potassium citrate and sodium bicarbonate as an alkalizing agents for the management of cystinuria. 10, 11, 17-20, 24-27, 29-34 5 studies reported the detail concentration of alkalizing agents used and their outcome of treatment (Table 4). 11, 17, 18, 26, 32 Potassium citrate (1mEq/kg/day, 11, 30 40-70mmol/day, 18 1000mg three times/day 32 ) and sodium bicarbonate (8-18gm/kg/day, 17 47.6-107mmol/day, 18 500mg four times/day 32 ) were recommended for all patients after cystinuria diagnosis.…”