Surgical interventions for nephrolithiasis in ankylosing spondylitis and the general population.

OBJECTIVE: The aim of this study was to estimate rates and type of definitive surgical interventions for nephrolithiasis in Swedish patients with ankylosing spondylitis (AS) compared to the general population. MATERIALS AND METHODS: This national prospective cohort study linked data from Swedish population and healthcare registries. Incidence rates and interventions for nephrolithiasis during follow-up in patients with AS were compared to general population comparator (GPC) subjects. RESULTS: In total, 8572 AS patients were followed for 49,959 person-years and 39,639 matched GPCs were followed for 225,221 person-years. Mean age at study entry was 46 years [interquartile range (IQR) 36-56 years] and 65% were male. In AS patients with a diagnosis of nephrolithiasis during the study period, 29% (72/250) underwent similar intervention for nephrolithiasis compared to 24% (114/466) GPCs (p = 0.21). The incidence rate ratio (RR) in overall AS patients was 2.9 [95% confidence interval (CI) 2.1-3.8] during a median follow-up of 6.2 years (IQR 3.2-8.6 years). With prior diagnosis of nephrolithiasis, the RR for AS patients compared to GPCs was 3.7 (95% CI 1.8-7.7); without prior nephrolithiasis the RR was 2.1 (95% CI 1.5-3.0). Increasing age [odds ratio (OR) 1.02, 95% CI 1.01-1.03], prior nephrolithiasis diagnosis (OR 3.3, 95% CI 1.97-5.62) and atherosclerotic cardiac disease (OR 2.0, 95% CI 1.03-3.91) were identified as predictors of intervention for nephrolithiasis. CONCLUSIONS: Patients with AS have an almost three-fold increased risk of surgical intervention for kidney stones, with similar management, compared to the general population.

Is nephrolithiasis an unrecognized extra-articular manifestation in ankylosing spondylitis? A prospective population-based Swedish national cohort study with matched general population comparator subjects.

BACKGROUND: Ankylosing spondylitis (AS) is associated with several extra-articular manifestations. Nephrolithiasis (NL) has not been recognized as one of those, however, several factors known to increase the risk of NL are at play in AS patients. The objective was to estimate rates and predictors of NL in Swedish patients with AS compared to the general population. METHODS AND FINDINGS: We performed a prospective population-based nationwide cohort study based on linkage of data from Swedish registries. 8,572 AS patients were followed for 49,258 person-years (py) and 39,639 matched general population comparators were followed for 223,985 py. Patients were followed prospectively together with comparator subjects from January 2001 through December 2009. The first occurrence of NL during follow-up was the primary outcome. Hazard Ratios (HR) were used to compare these rates adjusting for comorbidities and treatment, and to assess predictors for NL. Mean age at study entry was 46 years (inter quartile range 36-56 years), 65% were males. Based on 250 vs. 466 NL events, the adjusted HR of NL in AS patients was 2.1 (95%CI 1.8 to 2.4). Predictors of NL within the AS group included prior diagnosis of inflammatory bowel disease (IBD) (HR 2.3; 95%CI 1.7 to 3.3), prior diagnosis of NL (HR 16.4; 95%CI 11.5 to 23.4), and patients receiving anti-TNF treatment (HR 1.6; 95%CI 1.2 to 2.1). Male sex was a risk factor for NL both in AS patients and in the general population. LIMITATIONS: The risk for residual confounding and inability to study the chemical nature of NL were considered the main limitations of the study. CONCLUSIONS: Patients with AS are at increased risk of NL, which may be considered a novel extra-articular manifestation. Previous history of NL, IBD, AS disease severity and male sex were identified as predictors of NL in AS.