Case Presentation:
A 28 year old male presented to clinic with a painless, progressively enlarging mass in his right testis for 4-6 weeks. On examination a large, firm, right scrotal swelling was present. Testicular ultrasound revealed a heterogeneous 6.2 x 4.1 x 6.5 cm solid mass in the right testes. Labs were notable for a significantly elevated human chorionic gonadotropin (HCG) level of 1,414,442.8 IU/L, with a slightly elevated lactate dehydrogenase (LDH) of 1014 U/L, and normal alpha fetoprotein (AFP) of 3.3 ng/ml. CT scan of the chest and abdomen demonstrated metastasis to the lung, liver and retroperitoneal lymph nodes. Surgical intervention was advised, and a right inguinal orchiectomy was performed. Testicular pathology was consistent with choriocarcinoma with vascular invasion. Immunohistochemical staining was performed and was positive for HCG and pancytokeratin, confirming malignant choriocarcinoma as the diagnosis.
Chemotherapy was recommended and the patient was scheduled for port catheter placement. Post procedurally the patient developed atrial fibrillation with rapid ventricular response. Work up of atrial fibrillation included a normal echocardiogram, troponins, and electrolytes but was significant for a low thyroid-stimulating hormone (TSH) of 0.005 mU/L, high free thyroxine (T4) of 3.3 ng/dl and high free triiodothyronine (T3) of 11.69 pg/ml. Thyroid stimulating immunoglobulin was negative. A final diagnosis of paraneoplastic hyperthyroidism secondary to metastatic choriocarcinoma was made. The patient was administered chemotherapy for choriocarcinoma and methimazole for hyperthyroidism. Our patient responded well to chemotherapy and within months his HCG returned to normal levels with subsequent resolution of hyperthyroidism.
Discussion: Approximately 5-6 cases of testicular cancer per 100,000 males are reported each year with malignant choriocarcinoma representing less than 1% of all germ cell tumors. Paraneoplastic syndromes are triggered by functional peptides secreted by a tumor. Paraneoplastic hyperthyroidism is a rare finding associated with metastatic choriocarcinoma. The HCG hormone is structurally homologous to TSH, which can lead to stimulation of the TSH receptor. The laboratory profile mimics primary hyperthyroidism with a low TSH level and elevated free T4 and T3 levels. A paraneoplastic hyperthyroidism is usually seen in patients with HCG levels above 50,000 IU/L and improves as the underlying cancer is treated with chemotherapy.
Conclusions:
This case draws our attention to a rare case of hyperthyroid paraneoplastic syndrome associated with choriocarcinoma. It illustrates the importance of evaluating for hyperthyroidism in all patients with high HCG levels associated with choriocarcinoma.