Distinguishing characteristics of idiopathic calcium oxalate kidney stone formers with low amounts of randall’s plaque

Background Overgrowth of calcium oxalate on Randall’s plaque is a mechanism of stone formation among idiopathic calciumoxalate stone-formers (ICSFs). It is less clear howstones formwhen there is little or no plaque. Design, setting, participants, & measurements Participants were a consecutive cohort of ICSFs who underwent percutaneous nephroscopic papillary mapping in the kidney or kidneys containing symptomatic stones and a papillary tip biopsy from a representative calyx during a stone removal procedure between 2009 and 2013. The distribution of Randall’s plaque coverage was analyzed and used to divide ICSFs into those with a high (³5%; mean, 10.5%; n=10) versus low (<5%; mean, 1.5%; n=32) amount of plaque coverage per papilla. Demographic and laboratory features were compared between these two groups. Results Low-plaque stone formers tended to be obese (50%versus 10%; P=0.03) and have a history of urinary tract infection (34% versus 0%; P=0.04). They were less likely to have multiple prior stone events (22% versus 80%; P=0.002) and had a lower mean 24-hour urine calcium excretion (187±86 mg versus 291±99 mg; P<0.01). Morphologically, stones from patients with low amounts of plaque lacked a calcium phosphate core by microcomputed tomography. Papillary biopsies fromlowplaque stone-formers revealed less interstitial and basement membrane punctate crystallization. Conclusions These findings suggest that other pathways independent of Randall’s plaquemay contribute to stone pathogenesis among a subgroup of ICSFs who harbor low amounts of plaque.