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Catastrophic APS — SCE Rheumatology MCQ

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HardSLE & Antiphospholipid SyndromeCatastrophic APSSCE Rheumatology

A 34-year-old woman with SLE and persistently triple-positive thrombotic antiphospholipid syndrome is taking warfarin with an INR of 2.6. Over 4 days, she develops painful widespread livedo racemosa with digital ischaemia, confusion and oliguric acute kidney injury. Her platelet count is 58 × 10^9/L and LDH is elevated; the blood film shows occasional schistocytes. Brain MRI demonstrates multiple acute infarcts, and a skin biopsy shows non-inflammatory small-vessel thrombosis. ADAMTS13 activity is 46%. She is afebrile, blood cultures are negative and fibrinogen is normal. Complement levels and anti-dsDNA titres are unchanged from baseline. What is the most likely diagnosis?

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Correct answer: C — Catastrophic antiphospholipid syndrome

This is catastrophic antiphospholipid syndrome (CAPS): an acute thrombotic storm involving at least three organs within one week in a patient with established antiphospholipid antibodies, with histological evidence of small-vessel thrombosis. Thrombocytopenia, raised LDH and limited schistocytosis may accompany CAPS. TTP is less likely because immune TTP usually has severe ADAMTS13 deficiency below 10%. Sepsis-associated DIC is unsupported by the absence of infection and preserved fibrinogen. Stable complement and anti-dsDNA levels, together with non-inflammatory thrombosis rather than vasculitis or immune-complex disease, argue against an SLE flare. HUS would not as readily explain this APS-associated, simultaneous cutaneous, cerebral and renal thrombotic pattern. Treatment should begin urgently with therapeutic heparin, high-dose glucocorticoids and plasma exchange and/or IVIg, while treating any precipitating factor.

Reference: Jacobs L et al. Diagnosis and Management of Catastrophic Antiphospholipid Syndrome and the Potential Impact of the 2023 ACR/EULAR Antiphospholipid Syndrome Classification Criteria. Antibodies. 2024;13:21. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10967298/