Paroxysmal Nocturnal Hemoglobinuria Presenting With Progressive Biventricular Thrombi

A 34-year-old previously healthy woman presented with right-sided, pleuritic chest pain three weeks after a viral respiratory infection. Labs revealed hemoglobin of 10.2 g/dL (nadir 7.0), platelets of 109 × 10⁹/L, LDH of 1129 U/L (Ref: 122-222 U/L), undetectable haptoglobin, indirect hyperbilirubinemia, and elevated reticulocytes. Troponins were elevated. CRP was 184 mg/L (Ref: ≤ 5 mg/L). Peripheral smear was without schistocytes. Direct antiglobulin testing was negative. Urinalysis showed microscopic hematuria and positive hemosiderin. Echocardiogram revealed normal left ventricular (LV) function with left lateral wall hypokinesis and a 2.5 × 3 cm LV thrombus. Cardiac MRI was concerning for myopericarditis and new right ventricular (RV) thrombus, later verified by biopsy. There was also an infarction of the RV endomyocardium. Anticoagulation was initiated. Bone marrow biopsy showed erythroid hyperplasia without clonal myeloid features. Flow cytometry showed 57% CD59 deficient red blood cells, 88% CD157 deficient monocytes, and 91% CD157 deficient neutrophils, consistent with a new diagnosis of paroxysmal nocturnal hemoglobinuria (PNH). She was urgently vaccinated against encapsulated organisms, treated with eculizumab, and given antibacterial prophylaxis. Follow-up imaging showed near resolution of thrombi; hemoglobin and hemolysis markers normalized. PNH is a clonal hematopoietic disorder causing complement-mediated hemolysis and thrombosis. While thrombosis typically affects atypical venous sites, intracardiac thrombi are rare. PNH was the patient's only identified prothrombotic factor. This is the first reported case of intracardiac thrombosis in a previously healthy patient with new-onset PNH. Early recognition and complement inhibition are critical to reduce hemolysis, thrombosis, and mortality in PNH.