Endocrine Abstracts

Introduction: Graves’ disease is a common cause of hyperthyroidism in pregnant woman, but usually improves during pregnancy.

Case: A 23-year-old Pakistani woman in her first pregnancy had no personal or family history of thyroid disease. At 30 weeks gestation she developed a swollen, red left eye, which progressed to involve the right eye. Orbital MRI demonstrated left-sided proptosis, bulky superior and inferior rectus muscles, but no extra-orbital mass. Thyroid function tests showed biochemical euthyroidism (TSH 2.62 mIU/l, T4 11.7 pmol/l, T3 3.9 pmol/l). She was managed conservatively.

At 36 weeks gestation she suddenly developed loss of vision in the right eye, with bilateral opthalmoplegia. Visual acuity 6/12 left eye, and hand movement right eye. Anti-TPO (4 U/ml), anti-thyroglobulin (0 U/ml), and total TSH-R (5 U/l) antibodies were not raised. Treatment was initiated with intravenous methylprednisolone 1 g daily for 3 days, and then oral prednisolone.

Over the following week there was dramatic improvement in the opthalmoplegia, proptosis, and visual acuity (6/18 right and 6/4 left). She was discharged home at 38 weeks gestation, with the plan to await spontaneous vaginal delivery.

Further TSH receptor antibody assays were carried out, giving positive results: Thyroid stimulating antibody using cAMP bio-assay 186 pmol/l neat (negative control <5 pmol/l) and TSH binding inhibitory Ig assay 15% inhibition (positive >10%).

Discussion: It is unusual for Graves’ opthalmopathy to present de novo in pregnancy, and especially in a biochemically euthyroid woman, negative for conventional thyroid antibodies. The only case in the literature is a woman with known treated Graves’ disease.

It is hypothesized that differences in presentation of autoimmune thyroid disease during pregnancy is due to altered levels or ratio of blocking and stimulating antibodies. Although the commercial TSH-R assay did not demonstrate raised levels, the bioassay confirmed the presence of functionally active antibodies.