Correlation between orbital MR imaging and clinical activity score: prediction of the disease activity and CAS value.

Aim of the Study: Graves’ Ophthalmopathy (GO) is a chronic inflammatory autoimmune disease of periorbital tissue, conjunctiva and retrobulbar structures, e.g. ex- traocular muscles; more often associated with Graves’ hyperthyroidism. The predominant pathogenic factor is autoimmune attack by TSH receptor auto-antibodies, sharing as targets TSH receptors localized on orbital fi- broblasts and adipocytes, determining swelling of the ex- tra-ocular muscles and an increase in orbital connective tissue and fat volume, with consequent restrictive oph- thalmoplegia. Two phases characterize GO clinical course: 1) ”active phase”, presenting oedema and enlargement of muscles; 2) “inactive or chronic phase”, due to fibrosis and fatty infiltrations of muscles. Clinical evaluation must be integrated with imaging methods, i.e. orbital ecography, Computed Tomography, Magnetic Resonance (MR). Clini- cal Activity Score (CAS), proposed by Mourits, is a vali- dated scoring system, to distinguish inflammatory from noninflammatory GO. The purpose of our study is to dem- onstrate the statistically significant correlation between CAS and signal intensities on orbital MRI with contrast administration. Materials and Methods: An observational study has been conducted, including sixteen consecutive GO pa- tients and six normal volunteers. Patients were clinically observed using CAS by two different “blinded” operators. Orbital MRI was performed on a 1.5 Tesla MR Unit. MR scans were assessed by an experienced neuroradiologist, blinded to the clinical examinations, positioning ROIs around the edges of right and left inferior and medial rec- tus muscles, on coronal acquisitions. Results: Spearman’s rank correlation coefficient was used to analyse correspondence between signal inten- sity values and CAS. Significant statistic correlation was found between STIR signal intensity values and CAS. Sig- nal intensity values in enhanced-T1 sequences also cor- relate with CAS and with those detected on STIR images. Conclusions: Early diagnosis avoids permanent injuries (proptosis, sight impairment).CAS scoring system evalu- ates disease activity and response to immunosuppressive therapy, but actually does not fully describe the overall status of GO. MRI allows to discriminate active from inac- tive phase, choosing right treatment. Short Time Inver- sion Recovery sequences have been found useful in de- tecting oedema in extra-ocular muscles. We prove signal intensities values on STIR sequence increase in inflamma- tion oedematous phase and the direct proportion between STIR values and enhanced-T1 ones. We confirm the cor- relation between signal intensities on this sequence and CAS. Our study supports the diagnostic accuracy of the clinical score and its prediction capabilities in patient with Graves’ disease, to fit imaging with clinical evaluation, re- sulting in more objective assessments and fair treatment settings or even pre-clinical information.