C44-11 Hidden in Plain Sight: Pulmonary Amyloidosis Masquerading as a Benign Hamartoma

Abstract Introduction Pulmonary amyloidosis is an uncommon and often overlooked cause of pulmonary nodules, capable of closely mimicking benign or malignant lung lesions and leading to diagnostic uncertainty. This case demonstrates how a lesion initially presumed to be a hamartoma was ultimately identified as pulmonary amyloidosis, underscoring the need for clinical vigilance in evaluating indolent or atypical pulmonary lesions. Description A 71-year-old woman with coronary artery disease, hypertension, diabetes, and asthma was being followed by pulmonology for stable, scattered pulmonary nodules, the largest measuring 1 cm over two years. She was later hospitalized for hemoptysis, and a CT chest revealed a lobulated nodule at the bifurcation of the distal left main bronchus with an endobronchial component. Despite high suspicion for malignancy, she declined a biopsy. Six months later, repeat CT showed mild progression of the endobronchial lesion, prompting bronchoscopy, which revealed a 90% partially obstructing mass in the distal left mainstem bronchus. The lesion was treated with cryotherapy, and biopsy revealed a hamartoma. However, follow-up imaging a few months later showed new and enlarging nodules. PET/CT identified multiple scattered nodules, and a new 10 mm left apical nodule suspicious for malignancy. IR-guided biopsy of this lesion revealed plasmacytoma with amyloid deposition, further classified as Amyloid Light Chain (AL) kappa-type. Retrospective review of the prior hamartoma specimen also revealed amyloid deposition. Laboratory studies showed kappa monoclonal gammopathy of undetermined significance (MGUS) without systemic or bone marrow involvement, supporting a diagnosis of localized nodular pulmonary amyloidosis. Given the stable clinical course and presence of only mild dyspnea, a conservative approach with surveillance was opted. Discussion Increased awareness of the diverse presentations and diagnostic challenges of pulmonary amyloidosis is essential to avoid misdiagnosis and guide appropriate management. In this patient, an endobronchial lesion initially diagnosed as a hamartoma was later found to harbor amyloid deposition, illustrating the potential for diagnostic pitfalls. While most nodular pulmonary amyloidosis cases are asymptomatic and incidentally discovered, they may be associated with plasma cell dyscrasias, indolent lymphoproliferative disorders, or autoimmune conditions, highlighting the importance of thorough evaluation to exclude systemic disease. Localized pulmonary amyloidosis generally carries an excellent prognosis and rarely progresses to systemic involvement, supporting conservative management with long-term surveillance. This case emphasizes the value of heightened clinical suspicion, comprehensive tissue analysis, as well as retrospective review when initial diagnoses are uncertain. It also highlights the importance of recognizing rare pulmonary entities to optimize patient outcomes. This abstract is funded by: None