Amiodarone Induced Thyrotoxicosis: Should Surgery Always Be Delayed?

Abstract

INTRODUCTION: Amiodarone induced thyrotoxicosis (AIT) is a serious complication of amiodarone treatment. After failure of medical treatment, total thyroidectomy allows to stop hyperthyroidism and restart the antiarrhythmic. CASE PRESENTATION: A 52 years old man with obstructive hypertrophic cardiomyopathy (OHCM), echocardiography with severe left ventricular hypertrophy, preserved systolic function, SAM phenomenon and dynamic subaortic gradient, who started amiodarone after six episodes of rapid atrial fibrillation and four electrical cardioversion (EC). Two weeks later presented chest tightness, dyspnea, insomnia, warmth and loss of 2 kg. Thyroid profile shows TSH<0.008 ng/dL, T4 7.22 ng/dL, T3 406 ng/dL with no history of thyroid disease. Amiodarone was stopped, initiating antithyroid drug, propranolol and dexamethasone. After poor response (fT4 11.41 ng/dL, T3 262.40 ng/dL) plasmapheresis was made and due to the nonimprovement (fT4 9.36 ng/dL, T3 297.46ng/dL) a total thyroidectomy with general anesthesia was decided. Esmolol was required as premedication with midazolam. Anesthesia induction with remifentanil, etomidate, rocuronium and maintained with sevoflurane was performed. An intraoperative EC and two more in early postoperative period was given. At 8th day postthyroidectomy presented a new episode of atrial fibrillation requiring amiodarone impregnation. T4 was progressive decreased and levothyroxine was started. DISCUSSION: Amiodarone may be the only effective antiarrhythmic. Its suspension can be followed by a rebound increase of triiodothyronine that can take months to resolve. AIT treatment includes antithyroid drugs, corticosteroids, betablockers at high doses and plasmapheresis that may temporarily improve the clinical situation. Thyroidectomy is most commonly performed under general anesthesia technique. Adequate premedication with esmolol to control heart rate and benzodiazepines for proper anxiolysis is recomended. Etomidate was used for its almost nonexistent cardiovascular effects. Neuromuscular blocking agents should be used with caution in hyperthyroidism by association with myopathy. During anesthesia maintenance, assumes particular importance the early detection of thyroid storm as well as hemodynamic changes associated to the OHCM. The aim is to preserve systolic volume, reduce contractility and sympathetic discharge, increase afterload, reducing oxygen demand and ensure a correct systemic vascular resistance. Intraoperative transesophageal echocardiography allows to detect early any mechanical dysfunction. CONCLUSIONS: Thyroidectomy is ideally performed when the patient is euthyroid however manifestations of thyrotoxicosis and its influence on cardiac function may precede surgery. Surgery seems to be an effective and safe option when hyperthyroidism unresponsive to medical treatment and amiodarone is required.