Laterality of nephrocalcinosis in kidney stone formers with severe hypocitraturia

Study Type – Aetiology (case series) Level of Evidence 4 What’s known on the subject? and What does the study add? Systemic urinary stone‐forming conditions such as hypocitraturia or cystinuria should theoretically lead to symmetric and diffuse stone formation. Small studies have shown that some patients with such conditions produce stones primarily on one side. No studies, however, have attempted to quantify the frequency at which such patients form stones asymmetrically. This study demonstrates that despite having a severe systemic condition such as hypocitraturia, patients frequently have asymmetric and focal nephrocalcinosis. This suggests that additional intrinsic local factors such as renal perfusion or vascular injury must also play a role in stone formation. OBJECTIVE To examine the hypothesis that the distribution of nephrocalcinosis in patients with severe hypocitraturia should be symmetric. PATIENTS AND METHODS Patients with profound hypocitraturia defined as a 24‐h urine citrate <50 mg at the time of initial presentation were identified from the metabolic stone clinic database at our academic medical center. Two independent blinded reviewers evaluated all of the abdominal radiographs for the segmental distribution of macroscopic nephrocalcinosis. RESULTS A total of 44 patients met study criteria, with an equal distribution of males and females and a mean age of 55.4 ± 13.7 years. Mean urinary citrate was 28 ± 11 mg/day. Nephrocalcinosis was present in at least one renal segment in 22 patients (50%). Of the 22 patients with nephrocalcinosis, 9 patients (41%) had unilateral nephrocalcinosis and 13 patients (59%) had bilateral nephrocalcinosis. Of the 35 kidneys with nephrocalcinosis, 14 kidneys (40%) had nephrocalcinosis in only one renal segment, 13 kidneys (37%) had nephrocalcinosis in two segments and eight kidneys (23%) had nephrocalcinosis involving all three segments. CONCLUSIONS Despite the systemic nature of severe hypocitraturia, nephrocalcinosis is frequently asymmetric and focal in nature. This suggests that local factors intrinsic to the renal medullary interstitium, such as vascular injury, must play a role in the formation of nephrocalcinosis. Further study to elucidate these intrinsic local factors may further improve the treatment and prevention of urinary stone disease.