Endocrine Abstracts

A 20-year-old man presented to his general practitioner in 1990 with 4-months history of general malaise. He was clinically and biochemically thyrotoxic. Carbimazole was started but the patient stopped treatment on his own after 2 months. Two years later he was referred to our department with severe thyrotoxicosis marked by lethargy, shaking, palpitations and weight loss (FT₄ 116.6 pmol/l (reference range 10–24.5 pmol/l) TT₃ 8.8 nmol/l (1.0–2.5 nmol/l), TSH <0.05 miu/l (0.2–5.5 miu/l)). He had generalised smooth enlargement of thyroid gland with audible bruits but no evidence of thyroid eye disease or pre-tibial myxedema. Carbimazole was re-started but compliance with treatment remained poor with persistence of hyperthyroidism suggested clinically and biochemically as well as by technetium uptake scan. In 1993 he was, therefore, treated with radioiodine 200 MBq followed by 6 months of carbimazole. In 1995 he became hypothyroid (TSH 20.7 miu/l) and was started on thyroxine replacement. He continued thyroxine (average dose 150 mg once a day) with regular monitoring of his thyroid function tests until Septemeber 2007 when he presented with shaking, headache and weight loss. Thyroid function tests suggested recurrence of thyrotoxicosis (FT₄ 29.8 pmol/l, FT₃ 12.8 pmol/l (3.5–6.5 pmol/l), TSH <0.05 nmol/l) which persisted despite withdrawal of thyroxine. Thyroid auto-antibodies were positive (Anti-TPO 361 u/ml (0–60 u/ml)). Initial treatment with carbimazole was followed by radioiodine therapy in February 2008. Two months later patient developed hypothyroidism (TSH 70.8 miu/l) and has continued thyroxine on latest review in September 2008.

Recurrence of hyperthyroidism after radioiodine induced hypothyroidism is rare, much rarer is recurrence of hyperthyroidism after 12 years of replacement therapy with thyroxine as seen in our patient. Our case highlights that although unusual, clinicians should be aware of this possibility. Indefinite follow-up of thyroid function tests, as suggested in RCP guidelines, is therefore essential.