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Lupus-Associated ITP — SCE Rheumatology MCQ

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ModerateSLE & Antiphospholipid SyndromeLupus-Associated ITPSCE Rheumatology

A 42-year-old woman with established SLE has persistent isolated thrombocytopenia, with a platelet count of 65 × 10^9/L. Her haemoglobin and leucocyte count are normal. Blood film shows no schistocytes, haemolysis markers and renal function are normal, and she has no neurological features. Anti-dsDNA titres and complement levels are unchanged, with no other clinical evidence of active SLE. Antiphospholipid antibodies are negative. Bone-marrow examination shows increased morphologically normal megakaryocytes without dysplasia. Historical records show that thrombocytopenia was present before hydroxychloroquine was started. What is the most likely diagnosis?

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Correct answer: B — SLE-associated immune thrombocytopenia (secondary ITP)

Explanation lettering: B = shown as A · E = shown as B · D = shown as C · C = shown as D · A = shown as E

E is correct. Persistent isolated thrombocytopenia below 100 × 10^9/L, with increased morphologically normal megakaryocytes, supports peripheral immune-mediated platelet destruction. In a patient with SLE, this is secondary immune thrombocytopenia after competing causes have been excluded. TTP would require microangiopathic haemolytic anaemia, typically with schistocytes and biochemical haemolysis; these are absent. Myelodysplastic syndrome would be suggested by marrow dysplasia and often additional cytopenias. Hydroxychloroquine can cause thrombocytopenia according to its UK SmPC, so it should not be dismissed categorically, but causality is excluded here because the thrombocytopenia predates treatment. The absence of other clinical activity and stable dsDNA/complement make a generalised SLE flare with marrow suppression unlikely, although normal serology alone would not exclude lupus activity.

Reference: Bashyal KP et al. Primary Immune Thrombocytopenic Purpura (ITP) and ITP Associated with Systemic Lupus Erythematosus: A Review of Clinical Characteristics and Treatment Modalities. International Journal of Rheumatology. 2024. https://pubmed.ncbi.nlm.nih.gov/37827694/