Endocrine Abstracts

Case history: A 27 years old lady having presented with a neck mass, underwent a total thyroidectomy for thyroid malignancy in 1967. Histology confirmed papillary carcinoma of the thyroid. In 1968, she complained of tiredness and mild neck swelling despite TSH suppressive therapy. Her thyroid uptake study showed a residuum of thyroid tissue within the neck. She went on to have radioiodine ablation therapy on two separate occasions. She responded well with no evidence of residual tumour. She was maintained on TSH suppressive therapy thereafter with levothyroxine.

During the follow up, at the age of 72 years she began to complain of low energy level, constipation and tiredness which warranted further investigations.

Investigations:: Blood results normal FBC, U&E, LFT, vitamin D and elevated calcium of 2.74 mmol/l and PTH of 10.1 (normal 2.5–7.6 pmol/l) pmol/l. DXA showed spine L1–L4, T-score −1.1, and left hip total T-score −1.7. Renal ultrasound scan showed no evidence of nephrocalcinosis.

Results and treatment: Biochemical profile was consistent with primary hyperparathyroidism.

Following discussion, the patient opted for conservative management.

Conclusion and point of discussion:: External beam radiation (5–30 Gy) is associated with a dose-dependent occurrence of primary hyperparathyroidism, following a latency period of 20–45 years. In contrast, radioiodine therapy delivers a local dose of radioactivity to the thyroid and adjacent parathyroid glands in the region of 50–100 Gy for benign disease. Radioiodine has been associated with an increased risk of hypoparathyroidism.

We hypothesise that our patient developed hyperparathyroidism as a consequence of her previous radioiodine therapy, the delivered dose to the parathyroids being relatively lower due to only a small amount of residual thyroid tissue at time of ablation. This case highlights the importance of being aware of to the long-term sequelea of radioiodine therapy and the need for continued observation.