H-magnetic resonance spectroscopy of retrobulbar tissue in Graves ophthalmopathy

Accumulation of glycosaminoglycans in the orbit may play an important role in the development of Graves ophthalmopathy. Therefore, it might be clinically useful to evaluate the concentration of glycosaminoglycans in the orbit in patients with Graves disease. We investigated the concentration of glycosaminoglycans in retrobulbar tissue using in vivo 1H-magnetic resonance spectroscopy.

A model solution of 1% chondroitin sulfate (one of the components of the glycosaminoglycans complex) was initially examined using 1H-magnetic resonance spectroscopy, and the resonance of chondroitin sulfate was identified. 1H-magnetic resonance-spectroscopy spectra of retrobulbar tissue were obtained in 16 normal volunteers (28 eyes) and 23 patients with Graves ophthalmopathy (36 eyes). The 1H-magnetic resonance spectroscopy spectrum of chondroitin sulphate in the retrobulbar in vivo tissue was identified by assignments through lineshape comparisons of spectra of the model solutions in vitro and the retrobulbar tissue in vivo. Chondroitin sulphate-peak/H2O-peak ratios were calculated. To verify the results of in vivo 1H-magnetic resonance spectroscopy, retrobulbar tissue samples from five patients, who underwent orbital decompression surgery, were tested for reactivity to chondroitin sulfate proteoglycan by enzyme-linked immunosorbent assay (ELISA).

Multiple peaks, with a large peak at 5.24 ppm, were observed in 1H-magnetic resonance spectroscopy spectra of the model solution. A peak at 5.24 ppm was also observed in spectra of the retrobulbar tissue in all of the normal subjects and the patients. The mean value of the 5.24 ppm-peak/H2O-peak ratio was 0.1781 (SD = 0.0498, range, 0.0775 to 0.2282) in the normal subjects and 0.2874 (SD = 0.1357, range, 0.1405 to 0.7377) in the patients. The 5.24 ppm-peak/H2O-peak ratios were significantly increased in the patients with Graves ophthalmopathy (P < .01). The 5.24 ppm-peak/ H2O-peak ratio was correlated with the chondroitin sulphate concentration in retrobulbar tissue samples as evaluated by ELISA (r = .69).

This study suggests that 1H-magnetic resonance spectroscopy of the retrobulbar tissue allows us to estimate the concentration of chondroitin sulphate proteoglycan in the retrobulbar tissue. 1H-magnetic resonance spectroscopy of the retrobulbar tissue may be a new clinical tool for the evaluation of Graves ophthalmopathy.