A 35 year-old man with myasthenia gravis (MG) who developed a rare lymphoma — called mucosa-associated lymphoid tissue (MALT) — in the thymus gland containing “extensive” amyloid deposits is described, for potentially a first time, in a case report.
The report, “Amyloid deposition in thymic extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue in a patient with myasthenia gravis: A case report” was published in the journal Thoracic Cancer.
MALT is a rare B-cell lymphoma that develops outside lymph nodes. MALT lymphoma has been previously linked to autoimmune diseases like Sjögren’s syndrome, and to conditions involving chronic inflammation.
This study describes a patient diagnosed with both MG and thymic MALT lymphoma, who underwent a total thymectomy, or surgical removal of the thymus gland.
The man came to the investigators’ clinic, in Korea, with a two-year history of shortness of breath (dyspnea) when doing physical activities.
Blood tests showed elevated levels of acetylcholine receptor (AChR) antibodies (7.83 nmol/liter, compared to a normal range of 0-0.5 nmol/liter). Antibodies against AChR are a well-known marker of MG and he was diagnosed with the disease.
Chest X-rays taken then also revealed a mass at the mediastinum — the chest cavity between the lungs that includes the heart, esophagus, and trachea. A computed tomography exam identified it as a 7.4 centimeter (cm) solid mass with dense calcification inside. Doctors found no evidence of invasion into surrounding organs.
At this point, clinical examination concluded that this mass was most likely a thymoma — a tumor of the thymus gland. The patient underwent a total thymectomy, a common surgery for such cases.
Followup analysis showed the mass was poorly defined but firm, with the maximum length of 7.5 cm and a calcified interior. Cancer cells stained positive for CD20, a marker of B-cells.
The tumor was also found to contain deposits of amyloids, protein aggregates rarely seen in MALT lymphomas. Most known cases with such aggregates progress slowly.
Reports of a MALT lymphoma with amyloid deposits have only been described in orbit, lung, soft tissue and breast tissue. No record exists of previous studies of these aggregates in the thymus, the researchers said.
His final diagnosis was a “thymic marginal zone MALT lymphoma with extensive amyloid deposition,” the report states.
Symptoms eased after the surgery, but the man’s levels of AChR were not seen to drop in an analysis performed two months after that procedure.
It is still not clearly whether thymic masses are associated with MG development, and further research is needed, researchers noted.
“Here, for the first time, we report a case of extensive amyloid deposition in thymic MALT lymphoma in a patient with myasthenia gravis,” the investigators wrote.
But, they added, further research is needed because it is not clear through this one case whether thymic masses are associated with MG development.
Rather, “based on the observation in this case, we emphasize the importance of considering thymic MALT lymphoma as one of the possible diagnoses in patients with a solid and cystic thymic mass and autoimmune disease, including myasthenia gravis,” they concluded.
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