Pulmonary coexistence of immunoglobulin light chain amyloidosis and light chain deposition disease: A case report

We report the case of a 73-year-old woman with diffuse pulmonary cysts and multiple nodules incidentally detected during the follow-up for chronic liver disease. High-resolution computed tomography revealed numerous thin-walled cysts, predominantly in the lower lobes, with randomly distributed nodules. Pathological evaluation of the surgical lung biopsy specimens revealed nodular deposits of eosinophilic, amorphous material with peribronchiolar lymphoplasmacytic inflammation and identified pulmonary mucosa-associated lymphoid tissue lymphoma. Congo red staining revealed coexisting positive and negative foci within a single nodule, whereas immunohistochemistry showed kappa (κ) light chain positivity in both. Laser microdissection with liquid chromatography-tandem mass spectrometry identified a κ light chain dominant signature with amyloid signature proteins in the Congo red-positive region, consistent with immunoglobulin light chain amyloidosis (AL) κ-type, and abundant κ light chain peptides without amyloid signature proteins in the Congo red-negative region, consistent with non-amyloid κ light chain deposition. Systemic evaluation revealed no extrapulmonary amyloid or light-chain deposition, whereas Sjögren disease was confirmed by serological testing and minor salivary gland histology. The patient was managed conservatively with surveillance and remained clinically and radiographically stable without disease progression for approximately 1 year. Pulmonary AL and light-chain deposition are rare lung disorders, and pathologically proven pulmonary coexistence is rare. This case may help delineate the clinicopathological features of pulmonary monoclonal light chain deposition disorders.