Thyrotoxicosis and Pregnancy

A 35-year-old woman became aware of a swelling in her neck about ten weeks before referral. She had been trying to conceive for ten months. She had had a missed abortion fi ve months earlier. Because of the neck swelling, her family doctor arranged thyroid function tests, which were in the thyrotoxic range on two occasions fi ve weeks apart: serum free thyroxine, 26 and 28 pmol/l (normal range, 11–23); serum free tri-iodothyronine, 10.9 and 11 pmol/l (normal range, 3.5–6.5); serum thyroid-stimulating hormone (TSH), <0.05 mU/l (normal range, 0.3–4.1). Her previous medical history included a partial thyroidectomy for thyrotoxicosis at the age of 24. Other than a goitre, she had no symptoms except increased appetite and a slight tremor, which she had been aware of for about eight weeks. Following the missed abortion, she had two normal menstrual periods. Her only medication was folic acid supplements. She worked part-time and had a two-and-a-half-year-old child. On examination she was of average weight. Her hands were warm and moist. There was a fi ne tremor. A previous thyroidectomy scar was noted. The right lobe of the thyroid was palpable and felt smooth. There was a bruit over the right thyroid lobe on auscultation. She had lid retraction and lid lag but no other signs suggestive of thyroid-associated ophthalmopathy (TAO) (Figure 1). Her pulse rate was 100 beats per minute and regular. Her blood pressure was 150/70 mm Hg. The rest of the examination was normal. Thyrotoxicosis is no more than a descriptor for a pattern of biochemical abnormalities. Before considering treatment, it is the clinician's task to defi ne the underlying cause, as an accurate diagnosis is an essential guide to the most appropriate treatment (Box 1). The most likely causes in this case were Graves disease, thyroiditis, toxic multinodular goitre (TMNG), and toxic adenoma. The hallmark of TMNG or toxic adenoma is the presence of one or more palpable thyroid nodules. In this case the patient had previously undergone a partial thyroidectomy and a vascular thyroid remnant was palpable on the right thyroid lobe. Post-partum thyroiditis occurs within 12 months of childbirth; a variant of this condition occurs after miscarriage. In this patient's case post-partum thyroiditis was unlikely because her previous pregnancy was 2.5 years earlier; however, the miscarriage fi ve months earlier may have been relevant. Viral thyroiditis is usually preceded by an upper respiratory tract infection and the thyroid …