MALT lymphoma of the thymus with Sjögren's syndrome: biphasic changes in serological abnormalities over a 4-year period following thymectomy.

Thymic mucosa-associated lymphoid tissue (MALT) lymphoma shows distinct immunological characteristics, such as the expression of the IgA isotype, the frequent presence of immunoglobulin abnormalities, and a strong association with autoimmune disease, especially Sjögren's syndrome (SjS). We report a case of thymic MALT lymphoma, who exhibited biphasic changes in her clinical characteristics during the 4-year observation period after thymectomy. A 71-year-old woman was admitted because of suspected SjS. A diagnosis of primary thymic MALT lymphoma was made, and SjS was confirmed. Serological abnormalities such as polyclonal hypergammaglobulinemia, IgA M protein, and elevated levels of rheumatoid factor were noted. These abnormalities improved rapidly after the thymectomy, but did not completely disappear. Interestingly, the remaining abnormalities, which can be ascribed to the proliferation of B cells throughout the body under the influence of SjS, have been improving slowly but steadily during the 4-year observation period. It is suspected that the removal of the tumor by thymectomy has more or less normalized the immunological environment and alleviated the SjS disease activity.