Primary thymic mucosa-associated lymphoid tissue (MALT) lymphoma with Sjogren's syndrome and diffuse cystic lung disease: a complex respiratory presentation of a multifaceted autoimmune disease.

Mucosa-associated lymphoid tissue (MALT) lymphoma is a rare form of B-cell lymphoma which can potentially affect the stomach, spleen, salivary glands, skin, lungs, orbit, and, rarely, the thymus. Patients with Sjögren's syndrome (SjS) are at a 15-20 times increased risk of developing lymphoma compared to the general population.Here, we present a case of primary thymic MALT lymphoma and associated diffuse cystic lung disease, incidentally identified on routine chest imaging. Thymic MALT lymphoma has to date been reported primarily in women of Chinese origin, mainly without cystic lung disease. Diffuse cystic lung disease is well documented in women with SjS and the differential diagnoses also include lymphangioleiomyomatosis, which occurs almost exclusively in women.In the case presented, CT and positron emission tomography-CT showed a large hypermetabolic anterior mediastinal mass, as well as multiple thin-walled bilateral pulmonary cysts of widely varying sizes, without abnormal uptake. The patient was largely asymptomatic. Lung function testing, however, revealed restriction rather than obstruction, which is unusual in diffuse cystic lung disease. Biopsy of the mediastinal mass confirmed thymic MALT lymphoma which was treated medically with resultant improved lung function. This case highlights the association between SjS and MALT lymphoma, illustrates features which enable distinction between different causes of cystic lung disease in SjS, and comments on the multiplicity of SjS-related lung manifestations.