Recurrent Pleural Effusion and Grade 3 Pyrophosphate Uptake in Cardiac Immunoglobulin Light Chain (AL) Amyloidosis: A Transthyretin Amyloidosis (ATTR) Phenocopy.

Cardiac immunoglobulin light chain (AL) amyloidosis classically presents with biventricular heart failure and increased wall thickness. Recurrent unilateral pleural effusion as the inaugural manifestation is rarely recognized, and grade 3 99mTc-pyrophosphate (PYP) uptake is conventionally attributed to transthyretin amyloidosis (ATTR) amyloidosis. We describe a 66-year-old woman with treatment-resistant heart failure with preserved ejection fraction who presented with refractory pleural effusion requiring three large-volume thoracenteses. Echocardiography showed concentric hypertrophy with apical-sparing strain, and PYP scintigraphy demonstrated grade 3 myocardial uptake. Serum free light chains revealed a markedly elevated lambda fraction (33,562 mg/L) with a profoundly suppressed kappa-to-lambda ratio (0.001), and bone marrow biopsy confirmed coexistent multiple myeloma. First-line plasma cell-directed chemotherapy was initiated, but the patient died of septic shock and multi-organ failure 60 days after admission. This case illustrates two underrecognized phenomena: refractory unilateral pleural effusion as an inaugural feature of AL amyloidosis, and PYP-positive scintigraphy mimicking ATTR despite biochemically confirmed AL disease. Plasma cell dyscrasia must be excluded before any PYP-based diagnosis of ATTR amyloidosis is accepted, and refractory unilateral pleural effusion in a patient with diuretic-resistant heart failure warrants systematic evaluation for cardiac amyloidosis.