The usefulness of quantitative orbital magnetic resonance imaging in Graves' ophthalmopathy

Two-thirds of patients with Graves' ophthalmopathy (GO) respond to immunosuppressive treatment (prednisone or orbital irradiation), but one-third do not respond. Responders are likely to be in the active, oedematous stage of the eye disease, nonresponders in the inactive fibrotic stage. Clinical distinction between the two stages can be difficult. Quantitative magnetic resonance imaging (MRI) might be helpful in this respect, as T2 relaxation times are longer in oedematous than in fibrotic tissues.

Prospective study on quantitative orbital MRI in healthy subjects and patients with moderately severe GO, evaluating T2 relaxation time of extraocular muscles (EOM): (a) in patients vs. controls, and (b) in patients, as a predictor of outcome to orbital irradiation.

Nine healthy volunteers and 64 consecutive patients with moderately severe untreated GO, who were euthyroid for > or = 2 months and qualified for orbital irradiation. T2 relaxation times were measured at the site of the largest diameter in all eight EOM of each subject. Baseline T2 values in patients were related to outcome of radiotherapy, as assessed by an independent observer 6 months later according to predefined criteria.

T2 relaxation times of the eight EOM were longer in GO patients than in controls: median [range] 126 [52--250] vs. 88 [50--126] msec; P = 0.003. Per subject the single eye muscle with the longest T2 time was selected to represent active inflammation (excluding the lateral muscles for technical reasons). Again patients were different from controls: 160 [68--250] vs. 103 [86--115] msec, P < 0.001. In the group of 34 responders to subsequent radiotherapy, these T2 times tended to be longer than in the 30 nonresponding patients: 168 [108--250] vs. 138 [68--216] msec, P = 0.07. Using a cut-off value of 130 msec (derived from a receiver-operator-characteristics curve) a positive predictive value of 64% and a negative predictive value of 92% for the outcome of radiotherapy was calculated.

Quantitative orbital magnetic resonance imaging was found to be less accurate in predicting successful outcome of radiotherapy than expected. It seems more useful in detecting the fibrotic end-stage than the active stage of Graves' ophthalmopathy. It is therefore of limited use in the decision whether or not to apply immunosuppression in patients with moderately severe Graves' ophthalmopathy.