Endocrine Abstracts

Background: Hypercalcaemia of hyperthyroidism via increased bone turnover is not uncommon, however it is usually mild and asymptomatic. Corrected calcium (cCa) concentrations ≥ 3.0mmol/l are seen rarely and tend to be associated with high TSH receptor antibodies concentration. Some of the less well-known effects include thymic hyperplasia (TH) and lymphadenopathy. TH is explained by thyroid hormone acting on thyrotropin receptors in thymic tissue to increase proliferation of thymic epithelial cells and thymic medullary lymphoid follicles. Thyroxine can also have a direct effect on lymph tissue causing lymphadenopathy, splenomegaly and lymphocytosis. Importantly, thymic hyperplasia and lymphadenopathy secondary to thyrotoxicosis are benign and reversible with treatment of hyperthyroidism.

Clinical Case: We present a case of a 79-year-old lady, who was admitted acutely to the Emergency Department with symptomatic hypercalcaemia manifesting as confusion, word-finding difficulty, anorexia and worsening lethargy over a period of 12 weeks. cCa on admission was 3.19 mmol/l (2.2-2.6 mmol/l), ALP 173 U/l (30-130 U/l), PTH was normal at 2.0pmol/l (1.8-6.8 pmol/l). Confusion screen revealed hyperthyroidism with free T4 49.2pmol/l (7.7- 15.1 pmol/l), TSH <0.01mu/l (0.34-5.6 mu/l). Low magnesium was also noted 0.38mmol/l (0.70-1.0 mmol/l). CT scan to screen for malignancy detected an enlarged thymus with calcifications and mediastinal lymphadenopathy. No malignancy was detected. An enlarged thymus was also noted on scan 5 years prior. Global heterogenous enhancement of the liver and spleen likely perfusional in nature was noted and was attributed to thyrotoxic state. Thyroid stimulating immunoglobulins returned strongly positive at 32.6IU/L (<0.1), confirming Graves’ Disease without associated goitre or thyroid eye disease. She was managed with intravenous pamidronate, fluids and started on carbimazole. She developed transient hypocalcaemia (cCa 2.05 mmol/l) and hypophosphatemia on days 8 – 11 post pamidronate reflecting hungry bone syndrome due to rapid cessation of bone resorption. Her calcium normalised by day 11 post pamidronate and was maintained in range with normalisation of thyroid function. Endobronchial ultrasound and lymph node sampling and interval scan was offered to further investigate the lymphadenopathy, but were declined by the patient.

Discussion: This case highlights the importance of thyroid function testing when investigating and managing hypercalcaemia as well as the relationship between thyrotoxicosis, increased organ perfusion and thymic hyperplasia, which is most often benign and reversible with appropriate management of the underlying thyrotoxicosis. While our patient declined lymph node biopsy, her lymphadenopathy was clinically consistent with her thyrotoxicosis in the absence of any other apparent sinister cause and red flags.