ABSTRACT

Background/Aims

Both extraocular muscle (EOM) and orbital fat are involved in Graves’ orbitopathy (GO) but their enlargement might occur with a different temporal pattern. Two GO subtypes have been described, one with predominant EOM enlargement and the other with prevalent fat tissue involvement. We longitudinally investigated the EOM in GO patients and their relationship with clinical activity.

Materials and Methods

By using a commercial software with a manual methodology we calculated from CAT scan EOM coronal area (CA) and total orbit coronal area (TOA) in 23 control subjects and in 32 patients with GO. The latter were studied both at presentation and 18 months later. Superior, lateral, inferior and medial EOM areas were selected. The Clinical Activity Score (CAS) was also measured.

Results

Orbital EOM CA/TOA ratio (OM/TOA ratio) after 18 months decreased in most GO patients indicating that EOM area decrement contributed significantly to OM/TOA ratio reduction. CAS decrease was significantly correlated to the OM/TOA ratio decrease .

Conclusion

An easy method to measure CA of orbit components allowed us to observe that in most GO patients the OM/TOA ratio decreases with time, suggesting that macroscopic EOM involvement occurs initially and resolve as the other aspects of the disease resolve, as indicated by the significant OM/TOA ratio correlation with CAS.