Abstract Introduction Catastrophic antiphospholipid syndrome (CAPS) is the fulminant form of antiphospholipid syndrome characterized by abrupt onset of small- and large-vessel thrombosis; historically reported mortality is near 50%, though more recent series suggest improved survival with prompt combination therapy. A high index of suspicion is essential for timely diagnosis and management. We present a case of diffuse alveolar hemorrhage (DAH) as the initial manifestation of CAPS. Case Presentation A 55-year-old male presented with a two-day history of non-productive, non-bloody cough, dyspnea, and malaise. Upon arrival, he remained normotensive but was hypoxic to 80%, prompting intubation. A CT angiogram revealed diffuse ground-glass opacities concerning for DAH, which was confirmed on bronchoscopy by fresh blood throughout the bronchial tree. He was started on empiric antibiotics and corticosteroids. His admission was further complicated by acute renal failure requiring dialysis, acute respiratory distress syndrome requiring proning and lung-protective ventilation, and an in-hospital cardiac arrest. Hematology was consulted for concern of CAPS given a positive DRVVT in the setting of DAH and multiorgan failure. The patient underwent therapeutic anticoagulation, plasma exchange (PLEX) four days after admission and remained on high-dose corticosteroids. Despite escalation — including inhaled nitric oxide and continued proning — his oxygenation progressively worsened. Given ongoing clinical decline, the family elected to withdraw care and the patient expired. Discussion CAPS classically presents with rapid multiorgan thrombosis over days and often leads to multiorgan failure; diagnostic criteria emphasize involvement of multiple organs, histologic microvascular thrombosis when available, and persistent antiphospholipid antibodies on repeat testing. As many patients lack a prior APS diagnosis, recognition is frequently delayed and initial antibody testing can be inconclusive. DAH is an uncommon but recognized and high-mortality pulmonary manifestation of APS/CAPS. Common precipitants include infection, surgery, trauma, changes in anticoagulation, substance withdrawal, and malignancy. When clinical suspicion for CAPS is high, therapy should not await full laboratory confirmation; recommended initial management is the combination of therapeutic anticoagulation, high-dose glucocorticoids, and adjunctive plasma exchange and/or IVIG(triple therapy), with cyclophosphamide used when systemic lupus is implicated and biologics such as rituximab or complement inhibitors considered for refractory cases. Conclusion This case highlights DAH as a presenting feature of CAPS. Contemporary reviews continue to report substantial mortality despite multimodal therapy; clinicians must therefore maintain a high index of suspicion, rapidly recognize evolving multiorgan thrombosis, and initiate empiric, combined therapy when CAPS diagnosis is likely, to improve the chances of survival. This abstract is funded by: Individual
Karakilic et al. (Fri,) studied this question.