ABSTRACT

flavoprotein (Fp), the ‘‘64 kDa protein’’ and G2s, the terminal fragment of the winged-helix transcription factor Fox p1, may be markers of eye muscle damage in patients with Graves’ hyperthyroidism. Here, we report upon the sensitivity and specificity of EMAb testing in patients with thyroid disorders with and without ophthalmopathy from a single center. Patient charts were reviewed and EMAb results correlated with clinical diagnosis and features of ophthalmopathy. A single endocrinologist assessed each patient and serum was tested for eye muscle antibodies and levels of free thyroxine (T4) and thyrotropin (TSH). Medical records, laboratory reports, and EMAb test results were reviewed and relevant clinical and biochemical findings extracted and entered into a database. One hundred and sixty-three EMAb tests were carried out on 99 patients. A statistically significant association between anti-G2s antibodies and clinical features of the ocular myopathy subtype of TAO, but not of the congestive ophthalmopathy subtype, was demonstrated. Anti-Fp antibody test results were not found to be significantly associated with any eye findings. We also report preliminary data on the first 15 patients with newly diagnosed Graves’ hyperthyroidism treated with radioiodine or antithyroid drugs and followed for 1 year or more. In the first 15 patients followed for 1 year or more, serum antibodies against both Fp and G2s were found to be significantly associated with Graves’ disease, but not other thyroid diagnoses. None of the four patients treated with antithyroid drugs developed autoantibodies or demonstrated features of extraocular disease. On the other hand, eye muscle antibodies were detected in eight of the nine patients treated with radioiodine, in five cases after therapy. Of the six patients who had eye muscle involvement as defined by increased intraocular pressure on upgaze, diplopia or restricted motility, all received radioiodine and had detectable serum autoantibodies. None of the results were statistically significant, possibly due to the small numbers of patients so far analyzed.

In conclusion, anti-G2s and anti-Fp antibodies are associated with clinical eye findings in patients with autoimmune thyroid disease and in patients with Graves’ hyperthyroidism

studied prospectively following treatment with radioiodine, but not antithyroid drugs. This suggests that EMAb testing may be of clinical use in evaluating ophthalmopathy in patients with thyroid autoimmunity and as markers for the eye disorder.

INTRODUCTION

Ophthalmopathy is a common manifestation of autoimmune thyroid disease. Periorbital swelling, exophthalmos, eyelid lag, and impaired vision may occur. From 25% to 50% of patients with Graves’ hyperthyroidism will have some features of ophthalmopathy (1–3). Patients with Hashimoto’s thyroiditis may also develop eye symptoms, although much less frequently. Thyroid-associated ophthalmopathy (TAO) may comprise two distinct subtypes, namely congestive ophthalmopathy and ocular myopathy (4–6). Congestive ophthalmopathy results from the swelling of the eyelid and surrounding orbital connective tissue (OCT). Clinically, this may result in a range of findings including eyelid lag and retraction, chemosis, conjunctival injection, orbital puffiness, redness and other signs of inflammation. Ocular myopathy results from autoimmune attack of extraocular muscle tissue. This results clinically in impaired extraocular muscle function and diplopia (4–6).

The mechanism for the development of the eye changes in patients with Graves’ hyperthyroidism is still unclear. Congestive signs may be caused by an autoimmune attack against OCT antigens such as the TSH receptor and collagen type XIII, possibly in association with impaired venous drainage from the orbit (7). Ocular myopathy appears to be immune mediated (1,3,8) although the identity of the prime target antigen(s) is unclear. Several markers of immune-mediated damage to eye muscles have been identified. In particular, serum antibodies against 64 and 55 kDa eye muscle membrane proteins have been found in patients with TAO (5,8,9). The 64 kDa eye muscle protein has been identified as the flavoprotein (Fp) subunit of the mitochondrial enzyme

succinate dehydrogenase (8). The novel thyroid and eye muscle shared 55 kDa eye muscle protein G2s has recently been identified as the terminal 141 amino acids of the winged-helix transcription factor Fox p1.

Anti-Fp and anti-G2s antibodies are detected in the serum of the majority of patients with TAO (reviewed in Ref. 2). However, it has not yet been conclusively determined that a positive EMAb test is a useful clinical marker of TAO. The relationship between treatment of Graves’ hyperthyroidism and ophthalmopathy is unclear. While some workers suggest that ophthalmopathy may worsen after radioiodine treatment, others have not found such an effect and the issue remains controversial (reviewed in Ref. 10). We are studying patients with newly diagnosed Graves’ hyperthyroidism treated with antithyroid drugs or radioiodine in a 2 year prospective study. All patients undergo an eye examination each 3 months, at which time serum is taken for EMAb testing. Here, we report results on the first 15 patients after 1 year of follow-up. We have also determined how such EMAb testing is associated with clinical findings in a well-characterized group of patients with TAO from one center.

CLINICAL SUBJECTS AND METHODS

Patients

The first study sample consisted of patients seen at the thyroid clinic of the Queen Elizabeth II Health Sciences Centre in Halifax, Nova Scotia. The same endocrinologist (JRW) saw all patients between April 1999 and September 2001. Patients were assessed for thyroid diagnosis and eye symptoms. Serum was sent for EMAb testing and T4 and TSH measurements. Patients with no eye findings who were sent for EMAb testing were taken as a control group. For patients who were seen more than once, each EMAb test and concordant TAO status was recorded as a separate entry in the study. Overall, 163 EMAb tests were performed on 99 patients, 91 females and 8 males. Their ages ranged from 18 to 82 years with a mean