An 18 year old male presented with dyspnoea, haemoptysis, weight loss and a large right testicular swelling. On examination he appeared cachectic, diaphoretic and tachycardic. A large firm non-fluctuant right-sided scrotal swelling was present. There were no signs of goitre or dysthyroid eye disease. Thyroid function tests revealed biochemical hyperthyroidism: [fT4 38.6 pmol/L (NR: 9.418.6), TSH <0.01 mu/L (NR: 0.34.4)]. CT chest demonstrated multiple large pulmonary metastases throughout both lung fields. Testicular ultrasound revealed a 10 cm solid right sided scrotal mass which appeared to entirely replace the right testicle. Human chorionic gonadotrophin (HCG) was measured and was found to be massively raised 1118053.0 U/L (NR: 05). A diagnosis of paraneoplastic thyrotoxicosis secondary to metastatic testicular choriocarcinoma was made. Transfer to the regional cancer centre for neo-adjuvant chemotherapy with a view to subsequent surgery was agreed. His condition deteriorated steadily and he died two days later of respiratory failure. Germ cell tumours produce HCG, of which the α subunit is identical to that of TSH. Thus, the massive rise in HCG associated with germ cell tumours can stimulate the TSH receptor, overcoming its lower binding to TSH-receptors than native TSH and inducing thyrotoxicosis. This case illustrates the rare occurrence of thyrotoxicosis arising as a paraneoplastic syndrome due to testicular choriocarcinoma. The presentation was significant for clinical features of apparent hyperthyroidism including diaphoresis, palpitations and weight loss that were attributable to his underlying neoplasm. It highlights the importance of a comprehensive clinical history and examination for patients presenting with hyperthyroidism.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.