Endocrine Abstracts

Background: Hashimoto’s thyroiditis and Grave’s disease are the common autoimmune diseases of thyroid gland across all age groups. Some patients with autoimmune hyperthyroidism can become hypothyroid however it is rare for patients with hypothyroidism to develop Grave’s disease. Although some cases have been reported in adults, this phenomenon is very rare in the paediatric age group.

Case: 13 year old Caucasian girl who was diagnosed with aplastic anaemia and treated with bone marrow transplant two years ago was referred to our endocrine clinic with history of neck swelling. On examination she had grade 2 goitre. Her initial investigations showed low Free T4 6.5pmol/l (9.0- 25.0), raised TSH >150 mIU/l (0.3-5.0) with elevated thyroid peroxidase (TPO) antibodies 329 IU/ml (0 -60). She was diagnosed with hypothyroidism secondary to Hashimoto’s thyroiditis and commenced on levothyroxine. The dose of levothyroxine was titrated to 100 mg once daily and her condition was stable for eighteen months. On routine monitoring, her Free T4 was raised (34 pmol/l) and TSH suppressed (<0.05 miu/l). She remained asymptomatic with no signs of hyperthyroidism. After excluding possibilities of drug overdose and drug interactions, the repeat thyroid function test (TFT) showed similar findings. The dose of Levothyroxine was weaned over next few months and eventually stopped. After 4 weeks her repeat TFT was still suggestive of hyperthyroidism {Free T4 43 pmol/l, TSH <0.05 miu/l and Free T3 22.6 pmol/l (3.5-6.5)}. She also developed increased sweating, palpitation, tiredness and sleep disturbance. We commenced her on Carbimazole and propanalol. Her Anti TSH receptor antibodies was positive 4.4 IU/l (0- 0.09) confirming a diagnosis of Grave’s disease. Her symptoms improved and she was maintained euthyroid on carbimazole 20 mg once daily. Her USS thyroid did not show any thyroid nodules.

Discussion: The pathophysiology for this rare transition is not clear and few hypotheses have been postulated in the literature. One of them was switching of balance between the types of TSH receptor antibodies from blocking to stimulating antibodies (1).

Conclusion: Patients with established autoimmune hypothyroidism can rarely develop hyperthyroidism. Hence regular monitoring of TFT and improved awareness about this phenomenon is important.