Dysthyroid Orbitopathy

Dysthyroid orbitopathy is frequent: it is responsible for 15% to 30% of all unilateral exophthalmos and 80% of all bilateral exophthalmos. Although CT scan is frequently thought to be the best technique, ultrasound is useful for the diagnosis: showing hyperreflective muscles, with normal tendons. Color Doppler imaging is as efficient as MRI to evaluate the degree of inflammation of the muscles: hypervascularization of the affected muscles. It is also useful to look for damage to the optic nerve: decrease in the peak systolic velocities of the central retinal artery, with a high resistive index or dark signal of the spectral analysis curve, and dilation and reverse flow in the superior ophthalmic vein. In standardized A-mode, validated muscle indices allow for grading the severity of the disease. Differential diagnosis of large extraocular muscles includes orbital inflammation, and tumoral or vascular causes (fistulae, ischemia or traumatism).