Thymus in Hashimoto's disease and focal chronic lymphoid thyroiditis

Managing thymic enlargement in Graves' disease

Thymic enlargement (TE) in Graves' disease (GD) is often diagnosed incidentally when chest imaging is done for unrelated reasons. This is becoming more common as the frequency of chest imaging increases. There are currently no clear guidelines for managing TE in GD. Subject 1 is a 36-year-old female who presented with weight loss, increased thirst and passage of urine and postural symptoms. Investigations confirmed GD, non-PTH-dependent hypercalcaemia and Addison's disease (AD). CT scans to exclude underlying malignancy showed TE but normal viscera. A diagnosis of hypercalcaemia due to GD and AD was made. Subject 2, a 52-year-old female, was investigated for recurrent chest infections, haemoptysis and weight loss. CT thorax to exclude chest malignancy, showed TE. Planned thoracotomy was postponed when investigations confirmed GD. Subject 3 is a 47-year-old female who presented with breathlessness, chest pain and shakiness. Investigations confirmed T3 toxicosis due to GD. A CT pulmonary angiogram to exclude pulmonary embolism showed TE. The CT appearances in all three subjects were consistent with benign TE. These subjects were given appropriate endocrine treatment only (without biopsy or thymectomy) as CT appearances showed the following appearances of benign TE - arrowhead shape, straight regular margins, absence of calcification and cyst formation and radiodensity equal to surrounding muscle. Furthermore, interval scans confirmed thymic regression of over 60% in 6 months after endocrine control. In subjects with CT appearances consistent with benign TE, a conservative policy with interval CT scans at 6 months after endocrine control will prevent inappropriate surgical intervention. Learning points: Chest imaging is common in modern clinical practice and incidental anterior mediastinal abnormalities are therefore diagnosed frequently. Thymic enlargement (TE) associated with Graves' disease (GD) is occasionally seen in view of the above. There is no validated strategy to manage TE in GD at present. However, CT (or MRI) scan features of the thymus may help characterise benign TE, and such subjects do not require thymic biopsy or surgery at presentation. In them, an expectant 'wait and see' policy is recommended with GD treatment only, as the thymus will show significant regression 6 months after endocrine control.

Astrocyte growth enhanced by culture supernatant of a cloned rat thymic myoid cell

A conditioned medium (CM) from a cloned rat thymic myoid cell (IT-45R92) was used to investigate a possible relationship between the thymus and brain. CM stimulated the DNA synthesis of the cultured perinatal rat brain cells and spleen myelo-lymphoid cells but not that of the other types of cells including dorsal root ganglia, spinal cord, heart muscle, skeletal muscle, kidney, liver, skin, and thymic fibroblasts. CM appeared to stimulate glioblasts to differentiate into mature astrocytes that have a characteristic intracellular fibrous structure and a glial fibrillary acidic protein. These results indicated that thymic myoid cells release (a) 'cytokine(s)' for the astrocytes and myelo-lymphoid cells, similar to a 'lymphokine' (glia cell stimulating factor, GSF) produced by murine and human lymphocytes stimulated with mitogens.