Severe Postpartum HELLP Syndrome: Is This Atypical Hemolytic Uremic Syndrome?

Introduction: Complement dysregulation is implicated in the pathogenesis of atypical hemolytic uremic syndrome (aHUS) and there is growing evidence to support its role in HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome. Here we present a case of post-partum thrombotic microangiopathy (TMA) in the setting of HELLP syndrome. Case Description: A 22 year old G1P0 Caucasian woman presents at 37 weeks gestation with abdominal pain and severe hypertension. Labs demonstrated hemoglobin 95, platelets 30, LDH 2597, schistocytes, severe transaminitis (AST 1845, ALT 830), and proteinuric acute kidney injury. She was diagnosed with HELLP syndrome and treated with anti-hypertensives and emergency Caesarean section. Unfortunately, the infant did not survive; there was no placental abruption. Platelets recovered by day 5 postpartum, LDH by day 7. However, renal function worsened and by day 6 postpartum, she required hemodialysis when creatinine peaked at 812. A renal biopsy revealed acute and chronic TMA. She did not have cortical necrosis. Further workup revealed normal C3, C4 and ADAMTS13 levels. Dialysis was stopped after two weeks. By 6 months, her renal function and proteinuria returned to normal. Complement function testing revealed negative complement factor H autoantibody, but elevated plasma C5b-9 level (0.42 mg/L, normal <0.3). Ex-vivo serum C5b-9 deposition on human microvascular endothelial cells was assessed both on resting (182%, normal <150%) and on ADP-activated endothelial cells (273%, normal <150%). This test was repeated 6 months postpartum when renal function had normalized, and results were persistently abnormal both on resting (215%, normal <150%) and on ADP-activated endothelial cells (282%, normal <150%). aHUS genetic testing was negative. Discussion: The severity of HELLP syndrome associated organ dysfunction prompted the assessment for aHUS. Identifiable aHUS genetic mutations only occur in 50% of aHUS patients; however, the persistence of increased C5b-9 deposition mimics the findings of patients who have aHUS (Noris, Blood, 2014). Complement function testing is not routinely assessed for postpartum HELLP, and these unique results suggest the patient may be at risk for recurrent TMA/aHUS, particularly if another pregnancy is being considered. Future research should explore which pregnancy associated TMA patients may benefit from anti-complement therapy.

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