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SLE TMA vs TTP — SCE Rheumatology MCQ

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HardSLE & Antiphospholipid SyndromeSLE TMA vs TTPSCE Rheumatology

A 55-year-old man with SLE develops acute kidney injury, thrombocytopenia, microangiopathic haemolytic anaemia with schistocytes, and fluctuating confusion. His anti-dsDNA titre has risen and C3 and C4 are low. PT, APTT and fibrinogen are normal; antiphospholipid antibodies and stool testing for Shiga toxin-producing Escherichia coli are negative. His blood pressure is 154/92 mmHg. Before receiving plasma products or plasma exchange, ADAMTS13 activity is 48% with no detectable inhibitor. What is the most likely diagnosis?

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Correct answer: E — Secondary thrombotic microangiopathy associated with active SLE

This is secondary TMA associated with active SLE: microangiopathic haemolysis, thrombocytopenia and acute organ injury occur during a serologically active lupus flare. Immune-mediated TTP can coexist with SLE, but it is characterised by severe ADAMTS13 deficiency, conventionally below 10%; the pretreatment activity of 48% with no inhibitor strongly excludes it. Evans syndrome causes autoimmune haemolytic anaemia and immune thrombocytopenia rather than schistocytic microangiopathic haemolysis. Normal coagulation studies and fibrinogen argue against DIC, while negative Shiga-toxin testing makes STEC-HUS unlikely. The absence of antiphospholipid antibodies and severe hypertension also removes important alternative causes of TMA. This diagnosis does not by itself prove a primary complement-mediated disorder, and treatment should be individualised with specialist rheumatology, nephrology and haematology input.

Reference: Yue C et al. Characteristics and Outcomes of Patients with Systemic Lupus Erythematosus-associated Thrombotic Microangiopathy, and Their Acquired ADAMTS13 Inhibitor Profiles. Journal of Rheumatology. 2018;45:1549–1556. https://pubmed.ncbi.nlm.nih.gov/35979405/