Bone metastasis of malignant thymomas associated with peripheral T-cell lymphocytosis

BACKGROUND: Malignant thymomas are rarely associated with bone metastasis and T-cell lymphocytosis. CASE PRESENTATION: A 47–year-old female patient was admitted to our hospital for ptosis. A diagnosis of malignant thymoma was made based on the thymectomy and pathological result. Peripheral T-cell lymphocytosis and bone metastasis were found later. T-cell lymphocytosis was relived after surgical and radiation therapy to the metastasis. CONCLUSION: Peripheral T-cell lymphocytosis is a rare paraneoplastic phenomenon associated with thymomas. This report is the first to describe an invasive thymoma with late bone metastasis accompanied with T-cell lymphocytosis. We should be aware of peripheral T-cell lymphocytosis in thymomas and it may contribute to a better understanding of the complex physiology and pathogenesis of thymoma.