Tumors in the thymus can lead to a malfunction of the immune system, and cause the appearance of ANCA-associated vasculitis, a case report suggests. However, the association is rare, and more cases are needed to establish a line of treatment.
The study, “Microscopic polyangiitis associated with thymic tumor: a case report and review of the literature,” was published in BMC Nephrology.
The thymus, which sits atop the heart, is a specialized organ of the immune system where T-cells are made. These cells travel throughout the body to help fight infection, disease, and foreign subtances; but when the thymus is faulty, the immune system may not work as it should.
Cases of thymus enlargement and thymic tumors have been associated with a variety of autoimmune diseases. In these cases, thymectomy (surgical removal of the thymus) often leads to remission of the immune disease.
Sometimes, patients with thymic tumors also have kidney damage, but cases of thymic disease associated with ANCA-associated vasculitis have rarely been observed.
In the study, researchers in Japan described the case of an 89-year-old woman diagnosed with microscopic polyangiitis (MPA) associated with a thymic epithelial tumor (thymoma).
The patient was admitted to hospital because she was experiencing fatigue, nausea, muscle weakness in the lower limbs, and paralysis of her eye muscles. The symptoms appeared two months prior and gradually worsened.
She had no family history of renal, bronchial, or autoimmune diseases, did not smoke, and was receiving treatment for high blood pressure.
A urine analysis showed proteins and blood in the urine and increased levels of serum creatinine and C-reactive protein, all of which indicated kidney damage.
Lab tests showed that the patient had anemia, normal levels of white blood cells, and anti-neutrophil cytoplasmic autoantibodies (ANCAs).
ANCAs are abnormal antibodies that attack healthy neutrophils, a type of immune cell, causing the inflammation and damage in small blood vessels normally seen in ANCA-associated vasculitis patients.
While ANCAs normally target one of two proteins in neutrophils — myeloperoxidase and proteinase-3 — the patient had both of these ANCAs and a third one targeting the azurocidin protein.
A kidney examination showed inflammation in the glomeruli — the small tubes that filtrate urine — and thickening of the blood vessel walls of the kidney. These results led to a diagnosis of microscopic polyangiitis.
Further exams suggested myasthenia gravis, a rare disease where the thymus makes faulty antibodies that cause muscle weakness. Therefore, the patient was diagnosed with thymoma-related myasthenia gravis.
The combination of the three conditions suggested a central deficiency in the patient’s immune system. The doctors decided not to remove her thymus due to her advanced age and because, in previous cases of co-diagnosis of thymoma and ANCA-associated vasculitis, removal of the thymus had led to vasculitis flares.
The patient received corticosteroids as a remission-induction therapy. Three months after treatment, her ANCA levels had decreased, symptoms had become milder, and tumor size was reduced by half. However, her renal function did not improve, and the patient was put on dialysis three months after hospitalization.
Cases of co-diagnosis of a thymic tumor and ANCA-associated vasculitis are rare, with seven previous cases reported. In most cases, there was an additional autoimmune disease — such as myasthenia gravis in this report.
“Thymic diseases might be associated with the pathogenesis of ANCA-associated vasculitis due to central T-cell tolerance,” the researchers said. However, it is difficult to establish a line of treatment due to the low number of cases.
“To establish a treatment for thymoma-associated autoimmune diseases, further case studies are necessary,” the researchers said.