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.
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