Conversion of Primary Hypothyroidism to Hyperthyroidism: A Case Report

Effects of block-replace regimen in patients with autoimmune hypothyroidism converted to Graves' disease

PURPOSE

We present two cases of autoimmune hypothyroidism converted to Graves' disease (GD) and their medical management.

METHODS

We tested thyroid function and thyroid antibodies and performed an ophthalmologic examination and neck ultrasound in two patients with autoimmune hypothyroidism converted to GD during a follow-up of several years.

CASE REPORTS

The first case is a 33 year-old woman with hypothyroidism due to Hashimoto's thyroiditis (HT). She developed signs and symptoms of hyperthyroidism after 7 years of treatment with the same dose of levothyroxine (LT4). Even when LT4 therapy was discontinued, she remained thyrotoxic, with mild Graves' ophthalmopathy (GO) and very high thyroid-stimulating hormone receptor antibodies (TRAb > 40 IU/L, reference range: <1.75 IU/L). Antithyroid medication was started on a titration regimen, without achievement of euthyroidism. She was switched to a block and replace regimen, using 20 mg of methimazole (MMI) and 75 mcg of LT4 daily, with normalization of thyroid hormones and improvement of GO without steroids. The second case is a 57 year-old man with a 2-year positive medical history of HT and 6 months of LT4 treatment. He developed hyperthyroidism and moderate-severe GO. Despite stopping LT4 and initiating antithyroid medication in a titration regimen, he did not achieve euthyroidism and had active GO. Pulse glucocorticoid therapy and switching to a block-replace regimen was required to achieve euthyroidism and reduce ocular proptosis and diplopia.

CONCLUSION

Spontaneous autoimmune conversion of hypothyroidism to hyperthyroidism can occur at any time: it is important to promptly identify these cases so as to manage them effectively.

Autoimmune Thyroiditis Shifting from Hashimoto's Thyroiditis to Graves' Disease

In 15-20% of cases, Graves' disease (GD) shifts to Hashimoto's thyroiditis (HT), while the shift from HT to GD is rare. We present a case of a patient in whom HT shifted to GD, along with a literature review. A 50-year-old woman with myxedema was diagnosed with Hashimoto's disease due to hypothyroidism and the presence of antibodies against thyroid peroxidase (TPOAb) and thyroglobulin (TgAb); she also had thyroid stimulating antibodies (TSAb) without any signs of GD. Although thyroid hormone replacement therapy improved her thyroid function, 2 months later, hyperthyroidism appeared and did not improve after discontinuation of the replacement therapy. The patient was diagnosed with GD, which improved with antithyroid agent administration. To date, only 50 cases regarding conversion from HT to GD have been reported. The median age is 44 years (range, 23-82 years), and the median time of conversion is 7 years (range, 0.1-27 years). The male-to-female ratio of HT conversion to GD is 1:9, closer to that of regular GD (1:10) than that of general HT (1:18). All patients received thyroid hormone replacement therapy for hypothyroidism due to HT. Continuous evaluation of TSAb levels is recommended in HT, particularly in cases of TSAb-positive and those under replacement, since it may help predict conversion to GD. Evaluating the clinical characteristics of patients with HT preceding GD is crucial to ensure appropriate treatment and reduce the risk of adverse events.

New-Onset Graves’ Disease in the Background of Hashimoto’s Thyroiditis: Spectrums of the Same Disease With Changing Autoantibodies

Hashimoto’s thyroiditis and Graves’ disease represent two spectrums of the same autoimmune thyroiditis. Evolution from Graves’ disease to Hashimoto’s thyroiditis is a common scenario but conversion is a rare occurrence that we observed in the presented case of a 56-year-old Hispanic female with a history of Hashimoto’s thyroiditis with positive anti-thyroperoxidase (TPO) antibodies who was euthyroid on levothbefore75 µg for six years prior to her presentation to the emergency department (ED) with complaints of palpitations, exertional dyspnea, and unintentional weight loss of 20 lbs for four months. The patient denied any recent change in levothyroxine dosage. The patient was noted to have tachycardia at rest, hyperdynamic circulation, and fine tremors on outstretched hands-on examination but no exophthalmos, thyromegaly, or pedal swellings. Her initial laboratory workup revealed thyroid-stimulating hormone of <0.01 mIU/L, with elevated free T3 and free T4 levels. Levothyroxine was held and beta-blockade therapy was started for symptom control. Further workup showed elevated thyroid-stimulating immunoglobulin and thyroid receptor antibody levels and normalization of anti-TPO antibody levels. The radioactive iodine uptake scan was initially delayed because the patient underwent a pulmonary angiogram in the ED. A later scan showed thyromegaly with heterogeneous uptake of 82% in both lobes. Hence, the patient was diagnosed with Graves’ disease and managed with radioactive iodine ablation therapy. On follow-up, the patient developed post-ablation hypothyroidism; she was started back on levothyroxine therapy and became euthyroid. This case highlights that patients can develop Graves’ disease in the background of a hypothyroid state, and this conversion might be postulated secondary to a combination of atypical destructive thyroiditis and a switch of autoantibodies from blocking to stimulating ones. Clinicians should suspect the possibility of changing antibodies when there is a change in the patient’s euthyroid state.