Atypical Hemolytic Uremic Syndrome Associated With Malignant Hypertension Presenting With Pulmonary-Renal Syndrome-like Symptoms.

Both atypical hemolytic uremic syndrome (aHUS) and malignant hypertension (MHT) are causes of thrombotic microangiopathy (TMA), and their coexistence has been reported. We describe a 22-year-old man who exhibited severe hypertension, pulmonary hemorrhage, and acute kidney injury. Laboratory evaluation revealed thrombocytopenia, microangiopathic hemolytic anemia, and severe kidney dysfunction, without evidence of retinal hemorrhage or renal artery stenosis. Given suspicion for MHT-related thrombotic microangiopathy or immune-mediated pulmonary-renal syndrome, antihypertensive therapy, continuous hemodiafiltration, corticosteroids, and plasma exchange were initiated. However, autoimmune serologic testing was negative, von Willebrand factor protease (ADAMTS13) activity was preserved without inhibitor, and stool cultures were negative, leading to discontinuation of plasma exchange and tapering of corticosteroids. Thereafter, hematologic abnormalities transiently improved, but kidney dysfunction persisted, and pulmonary hemorrhage and cytopenia recurred with a marked reduction in complement C3 despite stabilized blood pressure reduction. Plasma exchange was resumed, and ravulizumab was initiated. Kidney biopsy demonstrated ischemic glomerular changes without immune deposits and marked narrowing of the interlobar arteries. Although genetic analysis identified variants in complement-related genes, definitive causative abnormalities remained undetermined. The patient was discharged with recovered kidney function, normalization of complement proteins, and sustained hematologic remission. Collectively, this clinical course is compatible with aHUS. We consider that MHT might trigger overt aHUS with pulmonary-renal syndrome-like features.