The syndromes of thrombotic microangiopathy (TMA) are associated with acute kidney injury and end-stage kidney disease. TMAs typically present with thrombocytopenia and microangiopathic hemolytic anemia (ie, systemic TMA). Kidney-limited TMA can occur, although often overlooked and undertreated. In this study, we studied the etiology and outcome of kidney-limited TMA. Patients with TMA on kidney biopsy, either systemic or kidney-limited, were recruited and classified as definite complement-mediated (C-)TMA (ie, ≥1 pathogenic complement gene variant), probable C-TMA (ie, massive ex vivo C5b9 formation without a pathogenic complement gene variant), and non (n)C-TMA (ie, normal ex vivo C5b9 formation). Morphologic features of TMA on kidney biopsy and their clinical correlates were studied. Patients were classified as definite C-TMA (N = 14; 18%), probable C-TMA (N = 21; 27%), or nC-TMA (N = 42; 55%), including 51 (66%) out of 77 patients with kidney-limited TMA. Patients with definite and probable C-TMA often presented with hemolysis (79% and 62% vs 34%; P = .007), glomerular thrombosis (79% and 76% vs 43%), a higher creatinine level (974 and 502 vs 280 μmol/L; P = .001), and a younger age (33 and 33 vs 40 years; P = .029) as compared with nC-TMA. Morphologic features neither defined etiology nor differed between systemic and kidney-limited TMA. Eculizumab improved kidney outcomes in patients with kidney-limited C-TMA but not in those with nC-TMA akin to patients with systemic C-TMA. Kidney outcomes were not affected by chronicity grading on kidney biopsy. Kidney-limited TMA is common in diverse TMAs, including C-TMA. A kidney biopsy is needed to detect TMA at the earliest possible stage of the disease. Morphology does not allow for the identification of etiology, and patients with kidney-limited TMA should therefore be screened for complement dysregulation, having a major impact on treatment and prognosis.

Recent studies showed a high prevalence of monoclonal gammopathy (MG) in patients with thrombotic microangiopathy (TMA) aged over 50 years and suggested that complement dysregulation is pivotal for the disease to develop. Here, we studied this premise in seven patients with TMA and coexisting MG. Patients with TMA on kidney biopsy and/or peripheral blood were recruited from the prospective COMPETE cohort (NCT04745195) and Limburg Renal Registry. Patients were screened for complement dysregulation, including genetics/factor H autoantibodies (FHAA) and functional ex vivo testing on microvascular endothelial cells. Seven (8%) out of 84 patients with TMA presented with a coexisting MG. MG clustered in patients aged over 50 years (n/N = 6/32, 19%). C4 and/or C3 levels were low in three patients, while four patients presented with normal complement levels. None of the patients carried rare variants in complement genes. Massive ex vivo C5b9 formation on the endothelium was noted in one patient; purified IgG from this patient caused massive ex vivo C5b9 formation via the alternative pathway of complement activation, pointing to complement dysregulation in the fluid phase. Kidney biopsies from other nephropathies linked to MG rarely exhibited concurrent TMA (n/N = 1/27, 4%). MG clustered in patients with TMA aged over 50 years. TMA and coexisting MG represents a heterogeneous disease spectrum, including a small subset of patients who may present with complement dysregulation.

Thrombotic microangiopathies (TMAs) are severe endotheliopathies that can arise in pregnancy and require early recognition. Complement-mediated (C-)TMA should be differentiated from other endotheliopathies of pregnancy, as treatment differs. Here, we report on a case of a pregnant woman with acute kidney injury requiring hemodialysis due to C-TMA on the background of a pathogenic C3 variant at 28⁺⁵ weeks of gestation. Low soluble Fms-like tyrosine kinase-1 to placental growth factor (sFlt1/PlGF) ratio excluded preeclampsia. Eculizumab was started and therapeutic drug monitoring was applied for optimal dosing. Despite prolonged hemodialysis, fetal well-being was preserved and delivery was safely postponed till 34⁺³ weeks of gestation, resulting in a healthy neonate. We also separately report on sFlt1/PlGF ratios measured in a cohort of 11 patients with TMA and coexisting pregnancy. Ten (91%) out of 11 patients had low sFlt1/PlGF ratios, excluding preeclampsia. Thus, successful pregnancy in women with C-TMA can occur, and sFlt1/PlGF ratios may aid in clarifying the diagnosis and appropriate treatment.

Pulmonary hypertension (PH) is a serious condition linked to immune-system dysfunction. Myositis-specific/associated antibodies (MSAs/MAAs) play a role in idiopathic inflammatory myopathy (IIM) and interstitial lung disease (ILD), but their significance in PH remains unclear. We believe the presence of these antibodies may be underestimated. This study analyzed adult PH patients without pre-existing IIM for MSA/MAA prevalence using a line-blot assay. We compared PH patients with and without ILD signs to a cohort clinically suspected of IIM/ILD (n = 558). Our PH cohort (n = 121) showed a significantly higher prevalence of overall weak positive MSAs/MAAs and positive overlap syndrome-associated MAAs than the suspected IIM/ILD group (p < 0.001). Notably, MSAs/MAAs were found in PH patients both with and without ILD, though more prevalent in those with ILD. Anti-synthetase and anti-overlap syndrome antibodies were the most common. Our study is the first to systematically show a high MSA/MAA prevalence in PH without IIM presentation. This highlights the need to consider PH when diagnosing MSA/MAA-associated conditions. We recommend MSA/MAA screening for newly diagnosed PH, especially in those with ILD, for early detection and potential immunomodulatory treatment. Further research should explore the link between MSAs/MAAs and PH, and the value of monitoring patients with weak MSA/MAA positivity over time.