Amiodarone Induced Type II Thyrotoxicosis Requiring Thyroidectomy Four Months after Amiodarone Discontinuation

Introduction : The risk of AIT can persist for several months following amiodarone discontinuation. We report a case of severe AIT occurring four months after drug discontinuation, resulting in persistent atrial fibrillation and refractory to pharmacotherapy.

Case Description : A 75 year old woman with history of generalized anxiety disorder, ankylosing spondylitis and atrial fibrillation presented to the hospital with two weeks of palpitations, dyspnea, lower extremity edema, fatigue and heat intolerance. She was previously on amiodarone for 1.5 years for atrial fibrillation, with discontinuation four months prior at the time of successful ablation. She had no history of thyroid disease and TSH four months prior was 1.92uIU/mL (0.40-2.50). On presentation, she was found to be in atrial fibrillation with RVR, and with acute decompensated heart failure. On exam, she was tachycardic, normotensive and afebrile. Mental status was intact, and there was no thyromegaly, palpable nodules or exophthalmos. Labs revealed TSH of < 0.01 uIU/mL (0.40-2.50), free T4 of 4.91 ng/dL (0.7-1.7), and free T3 9.67 pg/mL(2.3-4.2). She underwent three cardioversions, which were unsuccessful. She was started on metoprolol, methimazole and prednisone for initial coverage of AIT type 1 and 2. TSI and TSH receptor antibody testing was negative, and neck ultrasound revealed a hypovascular, normal sized thyroid gland without meaningful nodularity, most consistent with AIT type 2. Her free T4 and free T3 continued to rise depsite maximal dosing of methimazole, and was associated with persistent, symptomatic atrial fibrillation with RVR. Given lack of response to pharmacotherapy, she underwent total thyroidectomy, prior to which she received plasmapheresis, with lowering of free T4. Pathology confirmed benign thyroid tissue, with evidence of inflammation and fibrosis, consistent with AIT type 2. Methimazole was discontinued on the day of surgery and following thyroidectomy, prednisone was tapered off. One week post-thyroidectomy, she was started on levothyroxine for hypothyroidism, with free T4 0.54ng/dL. Patient reported improvement in fatigue and palpitations following thyroidectomy, and her atrial fibrillation was adequately controlled on rate-control medications.

Discussion : This case highlights the potential for AIT to develop several months following discontinuation of amiodarone, and the importance of continued TFT monitoring. Onset of AIT following discontinuation, as well as after longer periods of use ( >30 months), is seen more frequently with type 2 AIT. Patients with AIT may initially present with recurrence of atrial fibrillation, which should prompt evaluation with TFT's and not be attributed to effects of amiodarone discontinuation alone.