From Famine to a Feast: Little Endogenous Thyroxine to Overproduction

Abstract

Objective: Spontaneous conversion of autoimmune hypothyroidism to Graves disease is a rare occurrence. We present a case of antibody-confirmed autoimmune hypothyroidism, in which the patient was on replacement therapy with levothyroxine for 8 years and had spontaneous conversion to Graves disease with positive thyroid-stimulating hormone receptor antibodies (TRAbs). Methods: A 79-year-old woman was evaluated for persistent fatigue following acute dermatomal herpes zoster. She had developed progressive tremor of the extremities and heat intolerance. Her other problems included Hashimoto thyroiditis and vitiligo, diabetes mellitus, cerebrovascular disease, coronary artery disease, osteoporosis, and hypercholesterolemia. Her medications included metformin, aspirin, lisinopril, atorvastatin, zoledronic acid, and levothyroxine. Clinical examination was notable for healed lesions of herpes zoster and hand tremors. Results: Laboratory evaluation revealed triiodothyronine level of 1.83 ng/mL (normal range, 0.80 to 2.00 ng/mL), free thyroxine level of 1.53 ng/dL (normal range, 0.93 to 1.70 ng/dL), and thyroid-stimulating hormone (TSH) level of 0.007 μIU/mL (normal range, 0.27 to 4.20 μIU/mL). Of note, TRAb was positive at 5.37 IU/L (normal range, 0.00 to 1.75 IU/L). Radioactive iodine uptake scan was normal. Conclusion: TSH-stimulation blocking antibodies cause hypothyroidism, whereas thyroid-stimulating antibodies are responsible for Graves hyperthyroidism resulting from overactivation of TSH receptors. Our patient was on stable dose of levothyroxine for 8 years without any complications. We hypothesize that the conversion of blocking to stimulating antibodies was induced by the stress of the herpes zoster infection. Factors that possibly increased her odds for this phenomenon included her gender, thyroid replacement therapy, advanced age, and a background of autoimmune hypothyroidism. This case highlights the critical need to recognize that this transition can occur, since it requires a reversal of treatment plans. Abbreviations: GD = Graves disease;HLA = human leukocyte antigen;HT = Hashimoto thyroiditis;T3 = triiodothyronine;T4 = thyroxine;TRAb = thyroid-stimulating hormone receptor antibody;TSAb = thyroid-stimulating antibody;TSH = thyroid-stimulating hormone