Objective: Pretibial myxedema (PM) is a manifestation of Graves' disease (GD). Currently, its diagnosis depends on physicians' observation and biopsy. No satisfactory, objective, and non-invasive tool is available to record and investigate lesions. Digital infrared thermal imaging (DITI) detects surface temperature, and sonography reflects composition changes in soft tissue. This study was aimed to observe changes in DITI and sonography in PM, and to evaluate their clinical usefulness.
Methods: Nineteen GD patients with PM, 22 GD patients with mild diffuse non-pitting edema over lower legs, 46 GD patients with normal appearance of lower legs, and 14 normal volunteers were recruited for observation with DITI; 8, 21, 21, and 11 of them respectively also received soft tissue sonography for investigating the pathogenesis of DITI change.
Results: Lower leg temperatures of normal volunteers decreased gradually from proximal to distal parts. In all 19 patients with PM, DITI showed abnormally low focal temperatures over the lesions. In GD patients with mild diffuse non-pitting edema and GD patients with normal appearance of lower legs, DITI showed abnormally low focal temperature in 90.9 and 65.2% of the patients respectively. Areas of clinically visible PM and low focal temperature detected by DITI were sonographically characterized with increased skin thickness, hypoechoic substance deposition in the cutaneous tissue, and blurred boundary lines between dermis and subcutaneous tissue. TSH receptor antibody level correlated positively and significantly with skin thickness change and adjusted temperature difference between the center of temperature defect and the surrounding skin (P=0.046 and 0.033 respectively).
Conclusions: By using DITI and sonography, we detected characteristic changes in PM. These techniques are helpful in recording and may be useful tools to detect early changes of PM.