Case Report: Thrombotic Microangiopathy Secondary to a Hypertensive Emergency Mimicking Atypical Hemolytic Uremic Syndrome

Thrombotic microangiopathy (TMA) is characterized by endothelial injury leading to microvascular thrombosis, microangiopathic hemolytic anemia, and thrombocytopenia. Distinguishing secondary TMA associated with hypertensive emergencies from atypical hemolytic uremic syndrome (aHUS) is often challenging, as both conditions can present with similar hematologic and renal abnormalities.Moreover, aHUS frequently presents with hypertension, and certain complement gene variants are associated with a slowly progressive clinical course, further complicating the differentiation from hypertension-induced TMA.We report a case of secondary TMA triggered by a hypertensive emergency that closely mimicked aHUS.

A woman in her 60s with polymyalgia rheumatica, on long-term oral prednisolone (PSL) therapy for eight years, presented with progressive stiffness of the lower legs in late June, year X. The PSL dosage was increased from 1 mg to 15 mg per day in response to her symptoms. At that time, her serum creatinine (Cr) level was 0.71 mg/dL.
On July 4, she was admitted to another hospital because of general fatigue, low-grade fever, and right upper abdominal pain. Acute cholecystitis was suspected, and she was treated with intravenous antibiotics and fasting. During hospitalization, her blood pressure remained at 140–160/80–100 mmHg, and her serum Cr level increased to 1.19 mg/dL.
By July 9, her serum Cr level had further increased to 3.18 mg/dL, accompanied by proteinuria (urine protein-to-creatinine ratio [UP/UCr], 1.03 g/gCr) and hematuria (50–100 red blood cells per high-power field [RBCs/HPF]). Despite the resolution of cholecystitis, her renal dysfunction progressed, and she was subsequently transferred to our department for further evaluation and management.

At admission, the patient’s blood pressure was markedly elevated at 180–200 mmHg, and antihypertensive therapy with a calcium channel blocker was initiated on day 1. Despite a reduction in blood pressure to approximately 140 mmHg by day 2, renal function continued to deteriorate. By day 5, hemoglobin had decreased to 7.7 g/dL and platelet count to 92,000/μL, consistent with hemolytic anemia and thrombocytopenia. Serum haptoglobin was <10 mg/dL, and schistocytes were observed on peripheral blood smear, findings suggestive of TMA. After excluding thrombotic thrombocytopenic purpura (TTP), Shiga toxin–producing Escherichia coli (STEC)–associated hemolytic uremic syndrome, and other secondary causes of TMA, only aHUS and hypertension-induced TMA remained as potential diagnoses.
Hemodialysis was initiated on day 6. A renal biopsy performed on day 7 revealed endothelial injury with mesangiolysis and duplication of the glomerular basement membrane. Despite adequate blood pressure control, renal function and hematologic abnormalities did not improve, raising suspicion for aHUS. Plasma exchange and treatment with ravulizumab were therefore considered. However, from day 12 onward, renal function and platelet count began to improve, allowing discontinuation of dialysis on day 13. Thereafter, the platelet count continued to increase, reaching 361 × 10⁹/L by day 27. Renal function also showed sustained improvement, with serum creatinine levels remaining below 1.0 mg/dL. Given the recovery pattern following normalization of blood pressure, the final diagnosis was secondary TMA associated with a hypertensive emergency.

aHUS results from dysregulation of the complement pathway, whereas hypertensive TMA arises from endothelial injury secondary to an abrupt elevation in blood pressure. In the present case, hematologic and renal recovery following blood pressure control without the use of complement inhibitors supported a diagnosis of hypertension-induced TMA. Corticosteroid-induced hypertension has also been reported as a potential precipitating factor for TMA, and the recent escalation of prednisolone dosage in this patient may have contributed to endothelial injury. However, severe hypertension is observed in approximately 35–66% of aHUS cases, and slowly progressive variants, such as those associated with membrane cofactor protein (MCP/CD46) mutations, may show spontaneous remission but frequent relapses. Taken together, aHUS could not be completely excluded, and genetic testing should be considered if recurrence occurs.

We report a case of secondary TMA induced by a hypertensive emergency, which closely mimicked aHUS in both clinical presentation and pathological features. In case of TMA associated with severe hypertension, prompt and strict blood pressure control should be prioritized. Improvement in renal function and hematologic parameters following antihypertensive therapy provides a crucial diagnostic clue for differentiating hypertensive TMA from aHUS.