Subclinical alterations of extraocular muscles in Graves' Disease

Purpose: To evaluate the extraocular muscles involvement in Graves’ disease (GD) patients without signs of active Graves’ orbitopathy (GO). Patients were classified with Clinical Activity Score (CAS) proposed by EUropean Group of Graves' Orbitopathy. CAS is based on the presence of ocular symptoms: active lid swelling, eyelid erythema, definitive conjunctival redness, chemosis, caruncle or plical infiammation, spontaneous orbital pain, gaze evoked orbital pain. Methods: Sixty-four GD patients asymptomatic for active GO ( CAS ≤ 2) and spontaneous diplopia were studied. CAS classification of patients was represented by thirty-five with CAS 0 with no symptoms of GO, twenty-four patients CAS 1 presented only one GO symptom, and five patients CAS 2 with two GO symptoms. All cases underwent eye examination: biomicroscopy, visual acuity, intraocular pressure (IOP) in primary gaze and upgaze with corneal applanation tonometry, cover test, ocular motility examination, red filter test (RF) to identify latent diplopia fundus examination. Thyroid function (serum FT3, FT4 and TSH) and thyroid autoantibodies (TPOAb, TGAb and anti-TSH receptor, TRAb) were also performed. At the time of the enrollment, 25/64 (39,1%) patients were subclinical hyperthyroid and the remaining 39/64 (60,9%) were euthyroid under anti-thyroid drug therapy or after thyroid definitive cure. Results: Of nineteen patients that hadn’t IOP increase in upgaze or diplopia with RF, thirteen were CAS 0 and six were CAS 1. The remaining forty-five patients (70,3%) showed diplopia with RF or IOP increase in upgaze: 12/45 (26,6%) only IOP increase in upgaze, 13/45 (28,9%) only diplopia with RF, 20/45 (44,5%) patients had IOP increase in upgaze and diplopia with RF. Thirty-three patients showed diplopia with red filter test; 21/33 (63,3%) diplopia without ocular motility alterations, 17/35 were CAS 0 (48,6%), 11/24 were CAS 1 (45,8%) and 5/5 patients were in CAS 2 (100%). Conclusions: This preliminary study shows an high prevalence of subclinical extraocular muscle alterations in GD patients asymptomatic for active GO, which resulted unrelated to thyroid function tests. The red filter test showed hidden diplopia in 51,5% (33/64). The red filter test is easy and inexpensive; we propose its use for early diagnosis of active Graves’ Orbitopathy, and earlier treatment. Other investigations are needed to confirm these results