Clinical studies on thyroid CT number in Graves' disease and destructive thyrotoxicosis.

The purpose of the present study was to investigate by a computed tomography (CT) the Hounsfield unit (H.U.) of the thyroid in hyperthyroid and euthyroid Graves' disease and destructive thyrotoxicosis. The mean thyroid CT number in 95 controls was 122 +/- 18 H.U. (+/- SD) and did not change significantly with advancing age. The mean thyroid CT number (+/- SD) of 85 +/- 22 H.U. in 60 patients with hyperthyroid Graves' disease was significantly (P < 0.001) lower than either in normal controls or 116 +/- 22 H.U. in 11 patients with euthyroid Graves' disease (P < 0.001). Comparison of thyroid hormones and TSH receptor Ab values of untreated patients with a normal and an abnormally low thyroid CT number showed that serum total and free T3 were significantly (P < 0.05) higher in the latter group than in the former group. With respect to the effect of methimazole (MMI) on the thyroid CT number, in the untreated 10 patients with a low thyroid CT number, the initial mean CT number was 65 +/- 11 H.U. and increased significantly (P < 0.05) to 76 +/- 14 H.U. after treatment with MMI. In contrast, in 6 patients with a normal thyroid CT number prior to therapy, the initial mean thyroid CT number was 102 +/- 11 H.U. and fell significantly (P < 0.05) to 84 +/- 16 H.U. after treatment with MMI.(ABSTRACT TRUNCATED AT 250 WORDS)