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

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

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

Number of events and Incidence rates of first NL diagnosis during study period in AS patients (n = 8,572) compared to general population comparators (n = 39,639), overall and stratified by status on NL diagnosis prior to study entry.

<p>GPC; general population comparators.</p><p>py; person-years. Person years defined as starting at the date of entry into study (time of AS diagnosis, earliest Jan 1^st 2001) until first of death, emigration, nephrolithiasis diagnosis or end of study (Dec 31^st 2009).</p><p>IQR; interquartile range, IR; incidence rate, CI; confidence interval.</p><p>Number of events and Incidence rates of first NL diagnosis during study period in AS patients (n = 8,572) compared to general population comparators (n = 39,639), overall and stratified by status on NL diagnosis prior to study entry.</p

HRs (95%CI) for all covariates included in initial multivariate Cox regression model.

<p>HRs (95%CI) for all covariates included in initial multivariate Cox regression model.</p

Baseline characteristics of AS cohort and matched general population comparator subjects at study entry.

<p>Baseline characteristics of AS cohort and matched general population comparator subjects at study entry.</p

Incidence Rates (95%CI) of NL diagnosis in AS patients and general population comparators (GPC).

<p>Incidence Rates (95%CI) of NL diagnosis in AS patients and general population comparators (GPC).</p