A case of immune thrombocytopenia complicated by catastrophic antiphospholipid antibody syndrome and subsequent intramuscular haemorrhage.

backgroundImmune thrombocytopenia (ITP) and antiphospholipid syndrome (APS) are autoimmune disorders that may coexist, creating a challenging clinical scenario characterised by bleeding risk alongside paradoxically increased thrombotic risk. Catastrophic antiphospholipid syndrome (CAPS) is a rare but life-threatening manifestation of APS. The occurrence of CAPS in a patient with ITP receiving thrombopoietin receptor agonist therapy is uncommon and highlights important diagnostic and therapeutic challenges, particularly in the presence of concurrent bleeding manifestations. CASE PRESENTATION: A 51-year-old White British woman presented with new-onset immune thrombocytopenia that initially responded to corticosteroid therapy but subsequently relapsed, requiring treatment with avatrombopag. She later developed an unprovoked pulmonary embolism and, months afterward, rapidly progressive multiorgan thrombosis involving the kidneys, spleen, adrenal glands, retina, and brain following a urinary tract infection. Laboratory evaluation demonstrated a positive lupus anticoagulant and medium-titre anti-β2-glycoprotein I antibodies, supporting a diagnosis of probable catastrophic antiphospholipid syndrome. Avatrombopag was discontinued, and treatment with therapeutic anticoagulation, high-dose corticosteroids was initiated, resulting in clinical improvement. Her subsequent course was complicated by a large intramuscular thigh haematoma during anticoagulation and adrenal insufficiency secondary to bilateral adrenal involvement. Following further management, including rituximab therapy, the immune thrombocytopenia entered complete remission, and she remains on long-term anticoagulation and endocrine follow-up.

conclusionsThis case highlights the complex interplay between immune thrombocytopenia, antiphospholipid antibody positivity and thrombopoietin receptor agonist therapy. Clinicians should maintain a high index of suspicion for APS in patients with ITP who develop thrombotic events. Early recognition and treatment of CAPS are critical, even in the presence of significant thrombocytopenia, and careful balancing of thrombotic and bleeding risks is essential for optimal patient outcomes.