Relationship between magnetic resonance imaging signal intensity and volume of extraocular muscles in thyroid-associated ophthalmopathy with methylprednisolone pulse therapy

Purpose: To characterize the relationship between inflammation and swelling of extraocular muscles in thyroid-associated ophthalmopathy before and after methylprednisolone pulse therapy. Methods: The signal intensities and volumes of the superior rectus (SR), inferior rectus (IR), lateral rectus (LR), medial rectus (MR), and superior oblique (SO) muscles were measured with magnetic resonance imaging in 25 eyes of 25 patients with thyroid-associated ophthalmopathy in the acute inflammatory phase before and after methylprednisolone pulse therapy. The signal intensity ratios (SIRs) of muscles and brain white matter were calculated. Result: The mean SIRs before treatment were 2.28+/-0.74 in SR, 2.66+/-0.57 in IR, 2.03+/-0.42 in LR, 2.45+/-0.49 in MR, and 1.98+/-0.48 in SO muscles. The mean SIRs after treatment were 1.82+/-0.62, 1.84+/-0.52, 1.70+/-0.35, 1.95+/-0.46, and 1.60+/-0.36, respectively. The mean volumes (cm(3)) before treatment were 1.35+/-0.67 in SR, 1.21+/-0.39 in IR, 0.66+/-0.13 in LR, 0.94+/-0.31 in MR, and 0.58+/-0.14 in SO muscles. Those after treatment were 1.12+/-0.45, 0.91+/-0.31, 0.61+/-0.12, 0.85+/-0.28, and 0.49+/-0.11, respectively. The SIRs showed significantly positive correlations with volumes both before and after treatment in SR muscles (before, r=0.77; after, r=0.69), IR muscles (before, r=0.65; after, r=0.60), MR muscles (before, r=0.69; after, r=0.73), and SO muscles (before, r=0.52; after, r=0.50) (P<0.01 for all correlations). Conclusion: Swelling reflected the inflammation in extraocular muscles of thyroid-associated ophthalmopathy both before and after treatment.