Pulmonary Amyloidoma Discovered During Lung Cancer Screening

Abstract

INTRODUCTION: Primary pulmonary amyloidosis is a rare form of localized amyloidosis typically presenting incidentally as one or more lung nodules which can prompt a concern for pulmonary malignancy.CASE PRESENTATION: A 75-year-old woman with a 45-pack-year smoking history and family history of Waldenstrom macroglobulinemia in a first-degree relative was evaluated by low-dose CT scan for routine cancer screening and found to have a spiculated, noncalcified nodule of the right lower lobe measuring 1.9 cm x 1.6 cm with notable linear extensions toward the pleura. PET scan demonstrated the nodule to be hypermetabolic with a peak standard uptake value of 5.8 for 18-fluoro-deoxyglucose without any other areas of abnormal uptake. Navigational bronchoscopy to obtain transbronchial lung biopsies was nondiagnostic. She was referred to cardiothoracic surgery and underwent robotic-assisted right lower lobe wedge resection with mediastinal lymph node dissection. Histochemical staining of the nodule with Congo red was positive for apple green birefringence under polarized light compatible with amyloid. Mediastinal lymph nodes were negative for malignant process. Additional investigations in search of underlying conditions including lymphoproliferative disorders, plasma cell dyscrasias, infectious, or chronic inflammatory conditions were negative.DISCUSSION: Amyloidosis is a rare condition that can occur as either a systemic or localized process resulting from abnormal extracellular protein deposition. Approximately 6-10 cases occur annually per 100,000 in Western Europe and the United States with its exact incidence unknown. Primary pulmonary amyloidosis is seen when disease remains limited to the lung and occurs in three distinct forms: nodular parenchymal, diffuse alveolar-septal, and tracheobronchial amyloidosis, based on lung involvement and characteristic radiographic findings (1). Nodular parenchymal amyloidosis typically remains localized, often presenting incidentally in the 6th decade of life as one or more lung nodules known as amyloidomas. Diagnosis is confirmed upon biopsy with characteristic histological findings of eosinophilic material highlighted by Congo red staining demonstrating apple-green birefringence under polarized light. Prognosis is excellent provided no underlying process is identified with a disease-specific 10year survival of 96.0% for localized pulmonary amyloidosis compared to 51.9% for systemic amyloidosis (2).CONCLUSIONS: Although primary pulmonary amyloidosis remains a rare occurrence, it should be considered in the diagnostic workup of lung nodules. False-positive PET results can be seen in non-malignant disorders, highlighting a limitation of diagnostic accuracy (3).