Dr Lucy Birtwistle1, Dr Viduranga Wijeratne1
1Department of Renal Medicine, Gosford Hospital, Gosford, Australia
Biography:
Lucy Birtwistle is a Basic Physician Trainee with a budding interest in nephrology. She recently completed her term in renal medicine at Gosford Hospital and has trained as a junior doctor at Royal North Shore Hospital and Port Macquarie Base Hospital. She has an interest in clinical and translational research having studied medicine and advanced science at the University of Sydney. She has conducted research into therapeutic role of mesenchymal stem cell-derived extracellular vesicles in acute kidney injury, operative outcomes of adrenal tumours, CAR T-cell therapy, and presented a case on neonatal autoimmune haemolytic disease secondary to maternal Evans syndrome.
Background:
When a patient does not fit a familiar diagnosis, it is important to reconsider whether the sound of hooves signals zebras rather than horses. This challenge applies to diagnosing thrombotic microangiopathies (TMA), which are histologically characterised by microvascular thrombosis, and are associated with microangiopathic haemolytic anaemia (MAHA), thrombocytopenia, and end-organ ischaemia. TMA includes thrombotic thrombocytopenic purpura (TTP), Shiga toxin-producing Escherichia coli-mediated haemolytic uraemic syndrome (STEC-HUS) and complement-mediated TMA (CM-TMA).
Case Report:
We present a diagnostically challenging case of STEC-HUS in a 55-year-old female with a complex autoimmune history including ulcerative colitis (UC), primary sclerosing cholangitis, ankylosing spondylitis, hyposplenism, migraines, and pre-eclampsia. She presented with four days of bloody diarrhoea and abdominal pain and was initially managed as an UC flare. Subsequently, she developed MAHA, thrombocytopenia, and acute kidney injury (peak creatinine 834 µmol/L), raising suspicion for TMA. Diagnostic clarity was obscured by her UC background, adalimumab therapy, remote history of breast cancer, and alleged reports of Escherichia coli contamination in the local water supply. TTP was excluded by a normal ADAMTS13 level, and she received two doses of eculizumab to empirically treat for CM-TMA. Ultimately, stool PCR returned positive for Shiga toxin-producing Escherichia coli O157:H7, carrying the Stx 2c, Stx 1a subtypes, confirming STEC-HUS. She was transitioned to supportive care and received eight sessions of intermittent haemodialysis over 29 days of hospitalisation. At day 72, her renal function remains incompletely recovered (eGFR 28 mL/min/1.73m², creatinine 170 µmol/L).
Conclusion:
This adult case of STEC-HUS highlights the need to avoid diagnostic anchoring in patients with common conditions. It reinforces the need to “spot the zebra amongst the horses” in the timely identification and differentiation of TMA.