Use of MRI signal intensity of extraocular muscles to evaluate methylprednisolone pulse therapy in thyroid-associated ophthalmopathy.

PURPOSE

To quantitatively evaluate the efficacy of methylprednisolone pulse therapy for extraocular muscle inflammation in thyroid-associated ophthalmopathy (TAO) using the short-tau inversion-recovery (STIR) technique of magnetic resonance imaging (MRI).

METHODS

The signal intensities of the superior rectus (SR), inferior rectus (IR), lateral rectus (LR), medial rectus (MR), and superior oblique (SO) muscles were measured using the STIR images from 34 eyes of 17 patients with TAO before and after methylprednisolone pulse therapy and 19 eyes of 19 controls. The signal intensity ratio (SIR) of the signal intensity in muscles to that in brain white matter was calculated.

RESULTS

The mean SIRs of the controls were 1.08 ± 0.26 in the SR, 1.32 ± 0.29 in the IR, 1.34 ± 0.19 in the LR, 1.47 ± 0.25 in the MR, and 1.28 ± 0.22 in the SO muscles. SIRs exceeding 2.0 were out of the normal range. The SIRs of the patients with TAO before treatment were 2.19 ± 0.64, 2.44 ± 0.58, 1.96 ± 0.43, 2.24 ± 0.47, and 1.91 ± 0.42, respectively, which was significantly (P < 0.001) higher than those of the controls; after treatment, the mean SIRs were 1.82 ± 0.57, 1.81 ± 0.49, 1.64 ± 0.35, 1.88 ± 0.43, and 1.54 ± 0.33, respectively, significantly (P < 0.001) lower in all muscles than those before treatment. However, the SIRs of some muscles remained over 2.0. Moreover, all cases that had deterioration of TAO had one or more muscles with a SIR exceeding 2.5 after treatment.

CONCLUSION

Extraocular muscle inflammation in TAO improved with treatment. However, inflammation in some muscles persisted after treatment, and a high SIR in the muscle after treatment suggested the risk of deterioration of TAO.