A Challenging Case of Atypical Hemolytic Uremic Syndrome in a Young African American Patient
Authors: Vusqa Urwat Til , Asawa Palash , Samhouri Yazan , Bhagavatula Rama , Kaplan Robert B. 
Published: November 2021

Abstract
Background
It is known that malignant hypertension (mHTN) and thrombotic microangiopathy (TMA) commonly coexist. Deciding which phenomenon preceded the other remains a clinical dilemma, specifically in African American patients. However, making that determination is of utmost importance because the management will be different, and that can have dramatic effects on prognosis and outcomes. Herein, we report a case of atypical hemolytic uremic syndrome (aHUS) presenting as mHTN.
Case Presentation
A 35-year-old African American male with known history of hypertension, presented with nausea, vomiting, and diarrhea for four days. He also reported fatigue and exertional shortness of breath. Upon presentation, his blood pressure was 260/160 mmHg, otherwise physical exam was unremarkable. Initial work up showed hemoglobin of 8.8 g/dL (baseline 13.5), platelet count of 21,000/mL (baseline 250,000), serum creatinine of 16.99 mg/dL (baseline 0.99), MCV (84 fl), increased reticulocyte production index (3.58), increased LDH (1709 U/L), undetectable haptoglobin, and numerous schistocytes on peripheral blood smear. He was admitted as a case of hypertensive emergency and TMA. IV labetalol and hemodialysis were started. Given his gastrointestinal symptoms; stool for Shigella and E.Coli O157:H7 were checked and they were negative.
Given the severity of his hematologic derangements and difficult to control blood pressure, we decided to proceed with renal biopsy to rule out primary aHUS which showed thrombotic microangiopathy, global glomerulosclerosis, moderate interstitial fibrosis and tubular atrophy suggestive of aHUS or rheumatologic disorders like systemic sclerosis and arguing against malignant HTN as the sole player. ANA and anti-Scl-70 antibodies were negative. Final impression was aHUS by exclusion, and patient received meningococcal vaccines (Menactra and Bexsero) in preparation to start eculizumab. aHUS genetic panel was sent which came back equivocal as it showed mutations of unknown significance (homozygous missense mutation in the MASP2 gene and 2 heterozygous mutations in the C2 gene).
He was started on eculizumab 900 mg weekly for 4 weeks then 1200 mg biweekly starting week 5. He was seen in the office 2 months after initial presentation and receiving 5 doses of Eculizumab. His kidney function showed improvement with &gt; 2 liters of urine output daily, blood pressure was better controlled. A decision by nephrology was made to give him a break from dialysis and remains dialysis-free a year later.
Discussion
aHUS is a rare disorder with an estimated prevalence of seven per one million children in Europe. It causes uninhibited activation of complement factors that leads to renal endothelial damage and activation of coagulation cascade leading to TMA. The diagnosis of aHUS requires the fulfillment of the classical triad (microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure) with a positive gene mutation or antibodies to complement factors. However, absence of these mutations or antibodies, as in the presented case, do not exclude the diagnosis. The early diagnosis of aHUS is necessary for treatment with eculizumab, a monoclonal antibody against C5 to block the terminal complement cascade. Kidney biopsy can be helpful in equivocal cases especially if it shows only the typical changes of malignant hypertension which essentially rules out aHUS. Hypertension with concurrent TMA is treated with strict BP control which is often enough to resolve TMA features and restores renal function, at least partially. On the contrary, aHUS causing severe HTN needs more sophisticated testing and blockade of the terminal complement component to improve outcome; that's why the distinction of which one is the primary process is of utmost importance. Our case emphasizes the importance of having low threshold for testing for aHUS in patients with mHTN and TMA, especially in African American patients where malignant HTN is known to happen more commonly, and to notice the subtle hints that may help in this distinction, such as profound hemolysis or thrombocytopenia out of proportion to what one would expect from mHTN alone. Early recognition of aHUS may save a patient's kidney.

Disclosures
No relevant conflicts of interest to declare.