AN ULTRASTRUCTURAL AND SYSTEMIC ANALYSIS OF GLYCOSAMINOGLYCANS IN THYROID-ASSOCIATED OPHTHALMOPATHY

Purpose To determine the ultrastructural localisation of glycosaminogl ycans (GAGs) in the extraocular muscles (EOMs) of patients with thyroi d-associated ophthalmopathy (TAO) and to see whether the quantity and type of GAGs present in blood and urine are markers of the disease. Me thods Biopsies of affected EOMs were taken and studied by transmission electron microscopy (TEM). These were either fixed conventionally for TEM, or in 0.5% tannic acid and others for immunogold staining. Serum hyaluronan (HA) was measured using a radioimmunoassay in patients wit h TAO as well as control subjects, and urinary GAG levels assessed by photometric quantitation of hexuronic acid after reaction with carbazo le. The excretion pattern of the urinary GAGs was determined by discon tinuous electrophoresis. Results TEM showed that there is a marked exp ansion of the endomysial space in TAO EOM biopsies as compared with no n-TAO strabismus specimens. This is caused by an increased number of c ollagen fibres, interspersed with a granular amorphous material surrou nding striated collagen fibres shown to be hyaluronan by immunogold st aining. In contrast, serum hyaluronan concentrations were similar in T AO and control patients, although there was a statistically significan t difference in the urinary GAG excretion between the two groups of pa tients examined. By discontinuous electrophoresis, chondroitin sulphat e and heparan sulphate were present in both patients and controls. Con clusion GAGs and in particularly HA are present at the EOM level in pa tients with recently inactive TAO. However, serum levels of HA and uri nary GAGs are not sensitive indicators for their presence within the E OMs.