Uncommon Presentation of Undiagnosed B-Cell Lymphoproliferative Disorder as Nodular Pulmonary Amyloidosis.

B-cell lymphoproliferative disorders are characterized by the accumulation of mature B lymphocytes in the bone marrow, lymphoid tissues, and/or peripheral blood. They can cause amyloid deposits in the lungs. In rare cases, lung nodules can be the first sign of this disorder. We present the case of an 89-year-old woman with stable shortness of breath and lung nodules on imaging. A positron emission tomography-computed tomography (PET-CT) scan showed the most intense hypermetabolic nodule in the patient's lung, which was 1.5 × 1.4 cm. A biopsy of this nodule showed amyloid material with trapped plasma cell infiltrate on microscopy. Congo red stain under polarizing microscopy showed apple-green birefringence, which is diagnostic for amyloidosis. Immunohistochemistry showed a mixture of kappa-positive and lambda-positive cells. B-cell gene rearrangement-clonal gene rearrangements were detected in the immunoglobulin heavy chain (IgH) gene and the kappa light chain (IGK). These findings suggest a B-cell lymphoproliferative disorder, such as a plasmacytoma or a marginal cell lymphoma with plasma cell differentiation. The patient was diagnosed with a B-cell lymphoproliferative disorder and pulmonary amyloidosis. Isolated amyloidosis in the lungs usually has a good prognosis, but it can be a sign of autoimmune diseases or B-cell lymphoproliferative disorders, as in this case. Early diagnosis of B-cell lymphoproliferative disorder can lead to successful treatment and prevents complications.