This study reports a case of a 13-year-old male with a 3-year history of severe and intermittent hypokalemia episodes of unknown origin, requiring admission to the intensive care unit (ICU) for long QT syndrome (LQTS), finally diagnosed of redistributive hypokalemia secondary to the abuse of β-adrenergic agonists in the context of a probable factitious disorder.

BACKGROUND AND AIMS Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a necrotizing vasculitis characterized by inflammation of small blood vessels, being the kidney one of the most frequently affected organs. AAV has a high morbidity and mortality, developing rapidly progressive renal failure that could lead to end-stage renal disease (ESRD). The pathogenesis is complex and multifactorial; macrophages have turned out to be a key element in inflammation and also in fibrosis. As already described in previous publications, PR3-AAV and MPO-AAV show clinical-demographic differences and different renal phenotypes on kidney biopsy. Histopathological subgrouping into four classes (focal, crescentic, mixed and sclerotic, as defined by Berden et al.) was proposed to predict long-term renal survival rates, poorest in the sclerotic class. This classification, validated by our group and multiple others, is still under review. The aim of this study is to demonstrate whether interstitial fibrosis in AAV is at least as important as glomerular sclerosis in renal prognosis, being a differentiating element between MPO and PR3 vasculitis. METHOD We performed a retrospective single-center study of 95 AAV-patients (78 MPO-AAV and 17 PR3-AAV) diagnosed by renal biopsy from 1991 to 2021 and at least 1-year follow-up. Clinical and laboratory variables, presence and type of ANCA, immunosuppressant therapy and renal/patient survival were evaluated. Sixty-two kidney biopsy samples have been analyzed: histomorphometric quantification has been carried out using MetaMorph® software on trichrome-stained slides in order to measure the degree of fibrosis. Continuous variables were described using measures of central tendency and dispersion (mean and standard deviation), and categorical variables using frequency tables and percentages. Student's t-tests or Mann–Whitney U tests, as appropriate, were performed to evaluate differences in mean values, and chi-squared tests were used to evaluate differences in qualitative variables. Statistical significance was defined as P-values <.05. All P-values were two-sided. RESULTS PR3-AAV population was predominantly male (70%) with a mean age at diagnosis of 62 years and a mean follow-up of 54 months, while MPO-AAV population was mainly female (65.8%), mean age 66 years and follow-up 65 months. There were no statistically significant differences in renal function between MPO and PR3-AAV at diagnosis. However, our data showed that MPO-AAV had worse renal function than PR3-AAV at the end of follow-up (P = .01). Furthermore, it should be highlighted that renal function improved throughout the follow-up (P < .01 and P = .05 in MPO and PR3-AAV, respectively). From a histological point of view: MPO-AAV manifests more interstitial fibrosis at diagnosis than PR3-AAV (P = .01). However, there were no statistically differences in the amount of glomerular sclerosis. It is noteworthy that PR3-AAV showed more crescentic proliferation at diagnosis (P = .03) but less fibrotic crescents than MPO-AAV (not reaching statistical significance). CONCLUSION The method we used allows a quantitative assessment of renal fibrosis. Our data confirm that renal prognosis is better in PR3-AAV than in MPO-AAV, which could be explained by a greater interstitial fibrosis, as well as more fibrotic crescentic in MPO-AAV at diagnosis.

Background and Aims Primary Sjögren's syndrome (pSS) is a chronic systemic autoimmune disease, characterized by inflammation and destruction of the exocrine glands and the involvement of multiple organs. A wide variety of kidney manifestations associated with pSS have been described. The prevalence of kidney involvement is not clear. Our aim was to describe the renal involvement of patients with pSS diagnosed by kidney biopsy (KB). We also analyzed the clinical manifestations, laboratory and immunological characteristics, clinical outcomes and treatments received in patients with pSS referred to a specialized kidney centre. Method Observational, retrospective study of adult patients (age > 18 years) diagnosed with pSS (EULAR criteria) referred and treated at a kidney referral centre (Fundació Puigvert) in Barcelona, Spain. We collected data from the clinical records registry including demographic variables, laboratory parameters, biopsy results and adverse outcomes, defined by the need of renal replacement therapy (RTT) and/or death. Absolute frequencies, percentages, means and standard deviations were used for statistical analysis. Multivariate analysis was performed as appropriate in SPSS V28.0 Results A total of 27 patients with pSS underwent KB from January 1994 to July 2022; all patients were female, with a median age of 58.4 years (SD ±12.4); 85% were Caucasian. The mean baseline glomerular filtration rate (eGFR) was 65.9 mL/min (SD ±16) (before nephrologist referral), with 8 of 27 patients (29.6%) having eGFR less than 60 mL/min at baseline. The main indication for nephrological evaluation was acute kidney injury (AKI) (63%), followed by the presence of non-nephrotic proteinuria with dysmorphic haematuria (29.6%). The most common finding in KB was acute interstitial nephritis (AIN) (55.6%), as an isolated AIN kidney lesion in twelve patients (44.4%). Mild interstitial nephritis was noted in the context of a predominant glomerular lesion in three other patients (one membranoproliferative glomerulonephritis, one IgA nephropathy and one AA amyloidosis). Nine patients (33.3%) had glomerular lesion (see Table 1). In 18.5% of patients, the diagnosis of pSS was made after the renal biopsy. The percentage of patients receiving ACEI/ARB was 77.8%. A total of 25 patients received some type of immunosuppression (IS). Corticosteroids being the most frequently used (77.8%), followed by the combination IS treatment (44%) and rituximab (33.3%). At the time of the KB, the mean eGFR was 46.3 mL/min (SD ±24), compared to eFGR of 45.2 mL/min (SD ±22) one-year after KB. During follow-up, seven patients (25.9%) required RRT and three (11.1%) died from non-renal causes, mainly by infections associated with immunosuppression. Factors associated with adverse renal outcomes were AKI (p = 0.01), baseline eGFR CKD-EPI less than 60 mL/min (p = 0.005), presence of anti-Ro60 antibodies (p = 0.046), use of plasmapheresis (p = 0.013), use of cyclophosphamide (p = 0.013) and the presence of tubulointerstitial atrophy with glomerular sclerosis on kidney biopsy (p = 0.010). Conclusion Our study included a larger cohort than previously reported before in a single centre. In our cohort of patients with pSS who were evaluated by KB, AIN was the leading cause of renal involvement, as has been seen in other studies. The presence of eGFR below 60 mil/min at baseline and the finding of chronicity in the KB are associated with an adverse outcome, as well as is the presence of AKI. Early referral to nephrologist may be important for prognosis, and KB is necessary for accurate diagnosis of kidney involvement to allow targeted treatment.

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