Role of Diffusion-Weighted Magnetic Resonance (MR) Imaging in Differentiation Between Graves' Disease and Painless Thyroiditis.

Background: To assess the role of diffusion-weighted MR imaging in differentiation between Graves' disease and painless thyroiditis.

Material/methods: A prospective study was conducted among 37 consecutive patients with untreated thyrotoxicosis (25 female and 12 male; mean age of 44 years) and 15 ageand sex-matched controls. Diffusion-weighted MR imaging of the thyroid gland was performed in patients and controls. The apparent diffusion coefficient (ADC) value of the thyroid gland was calculated and correlated with Tc-99m uptake and thyroid function tests of the patients.

Results: There was a significant difference in the ADC value of the thyroid gland between patients and the control group (=0.001). The mean ADC value of the thyroid gland in Graves' disease was 2.03±0.28×10 mm/sec, and in patients with painless thyroiditis 1.46±0.22×10 mm/sec, respectively. There was a significant difference in the ADC values between Graves' disease and painless thyroiditis (=0.001). When the ADC value of 1.45×10 mm/sec was used as a threshold value for differentiating Graves' disease from painless thyroiditis, the best result was obtained with area under the curve of 0.934, accuracy of 83.8%, sensitivity of 95.8%, and specificity of 61.5%. The mean ADC value of the thyroid gland in patients positively correlated with serum TRAb and Tc-99m uptake (=0.57, =0.001 and =0.74, =0.001, respectively).

Conclusions: We concluded that ADC values of the thyroid gland can be used to differentiate Graves' disease from painless thyroiditis in patients with untreated thyrotoxicosis.