Endocrine Abstracts

Background: Neck irradiadion is associated with several complications including both hypo- and hyperthyroidism. We present a case of severe hypothyroidism, followed 5 years later by thyrotoxicosis.

Case description: A 27-year-old female presented with clinical and biochemical thyrotoxicosis (TSH 0.01 μIU/ml (ref. range: 0.27–4.2 μIU/ml); FreeT₄ 1.58 ng/dl (ref. 0.98–1.63 ng/dl); FreeT₃ 4.56 pg/ml (ref. 2.6–4.4 pg/ml). Clinical examination revealed tachycardia about 100 beats/min. and no obvious goitre. Autoimmune profile was suggestive of Graves’ disease (anti-TSH-receptor antibodies (aTSHR) 16.69 IU/l (ref. 0–1.75), anti-thyroid peroxidase antibodies (aTPO) 1780 IU/ml (ref.: 0–34 IU/ml). She had a history of Hodgkin’s lymphoma, diagnosed and treated with chemo- and radiotherapy (including the neck) at the age of 18. At the age of 20 she developed severe hypothyroidism (TSH >100 μIU/ml), with high titres of both aTPO (150 IU/ml) and aTSHR (37.56 IU/ml) antibodies. Thyroid function tests normalised after treatment with thyroxine (100 μg od). At the age of 26 she became ‘anxious’ and experienced ‘heart palpitations’. She was found to have suppressed TSH, that remained suppressed even when the dose of thyroxine was reduced and then discontinued. After further 4 months she was found to have raised free T₃ (see above). Thyroid scintigraphy revealed a normal and homogenous iodine uptake (41%). The patient responded very well to treatment with low dose thiamazole (10 mg od).

Conclusions: Our case illustrates that after neck irradiation, even severe hypothyroidism can be followed by thyrotoxicosis. There is a possibility that in this case there was a gradual switch from a TSH receptor blocking antibodies into TSH receptor stimulating antibodies.