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BackgroundKidney injury in mixed connective tissue disease (MCTD) is an uncommon manifestation. Prevalence has been reported to be <4% in some cohorts. The frequency of renal involvement in Hispanic patients with MCTD is not known.ObjectivesWe aimed to describe the prevalence, clinical characteristics and outcomes of renal involvement in Mexican patients with MCTD.MethodsWe conducted a retrospective single-centre study. We included patients with a diagnosis of MCTD according to the Alarcón-Segovia criteria who regularly attended to a referral centre in Mexico City (2003–2017) and we identified those with renal involvement defined as proteinuria >500 mg/d with or without active sediment, creatinine elevation 50% above baseline or development of glomerular filtration rate (GFR) <60 ml/min, with no other known cause. We collected demographics, clinical manifestations, follow-up time, treatment, outcomes and damage (SLICC/ACR-DI), renal function, serological and histological variables.ResultsOne hundred and thirty one patients with MCTD were followed at our centre. We identified 14 patients with renal involvement with a prevalence of 10.7%. Among those patients, 13 were women (92.8%); mean age at onset of renal involvement was 44±8 years. Most frequent manifestations were Raynaud’s phenomenon in 13 (92.8%) patients, arthritis in 12 (85.7%), puffy hands in 12 (85.7%), sclerodactily in 8 (77.1%), sicca syndrome in 8 (77.1%) and myositis in 7 (50%). Median time elapsed from MCTD diagnosis to renal involvement was 83 (2–365) months. In 3 patients, renal involvement was present at MCTD onset. Seven (50%) patients had other signs of MCTD activity at the time of renal involvement onset. Four (28.5%) patients presented with sub- nephrotic proteinuria, 3 (21.4%) with nephrotic range proteinuria and kidney injury, 2 (14.3%) with sub-nephrotic proteinuria and kidney injury, 2 (14.3%) with nephrotic range proteinuria, 1 only with nephrotic range proteinuria and 1 (7.1%) with end-stage renal disease. Microscopic hematuria was present in 9 (64.3%) patients and leukocyturia in 6 (42.8%). Renal biopsy was performed in 8 (57%) patients; pathological diagnoses were: crescentic and necrotizing glomerulonephritis (GN) (2 patients; one of these patients developed positive ANCA antibodies), GN ISN/RPS 2003 class III+V,1 GN ISN/RPS 2003 class III+V with thrombotic microangiopathy,1 GN ISN/RPS 2003 class IV+V and vasculopathy,1 membranous GN,1 minimal mesangial GN1 and chronic tubulointerstitial nephritis with vasculopathy.1 Ten (71.4%) patients achieved either total or partial remission at a median follow up of 82 (1–367) months. Only one patients required dialysis. At last follow up the median SLICC/ACR-DI was 1.5 (0–4) points. Two patients died.ConclusionsIn our cohort of MCTD patients, prevalence of renal involvement was low, although higher than the one reported in other populations. Clinical presentation and pathological diagnoses were diverse. Renal biopsy was helpful, since glomerulonephritis, vasculopathy and overlap with ANCA assoc...

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