Endocrine Abstracts

Introduction

The term factitious thyrotoxicosis is defined as an excess of thyroid hormone in the body caused by the ingestion of exogenous thyroid hormone. It can be intentional, usually in patients with psychiatric disorders, or accidentally. Another possible cause is the inappropriate use of thyroid hormone for the treatment of obesity, depression or infertility.

Case report

We present the case of a 32-year-old woman, with gestational hypothyroidism during her second pregnancy on treatment with Levothyroxine 50 µg and withdrawal of the treatment. She came to the clinic 2 years later, referring tachycardia, loss of 30 kg in the last 3 months, no fever or compressive symptoms. In laboratory tests she presented TSH 0.01 µIU/ml, FT4 57.67 pmol/l, T3L 14.1 pmol/l. Treatment with antithyroid drugs (Carbimazol 5 mg, 5 tablets a day) was started and a thyroid scintigraphy was requested. At the review appointment these were the blood test results: TSH <0.01 µIU/ml, FT4 97.39 pmol/l, FT3 18.1 pmol/l, TPO antibodies (TPOAb) 525.1 IU/ml, TSH receptor antibodies (TRAb) <0.8 IU/l. Thyroid scintigraphy showed absence of uptake. Due to the absence of improvement and the clinical repercussion of the patient, she was admitted to hospital for study and treatment. During admission, the patient remained in sinus rhythm with a heart rate between 60 and 100 bpm. Laboratory tests showed Thyroglobulin 1.68 ng/ml, Thyroglobulin antibodies (TgAb) <20 IU/ml. Whole body scintigraphy showed absence of thyroid uptake (ruling out struma ovarii), thyroid ultrasound with normal glandular size with heterogeneous echogenicity and no nodules. Serial analyzes were performed throughout one morning showing significant fluctuations in FT4 levels: 57.67 pmol/l – 76.98 pmol/l – 79.39 pmol/l – 80.55 pmol/l. The main suspicion was factitious thyrotoxicosis due to the coexistence of a high concentration of FT4 without thyroglobulin increase and the absence of uptake on scintigraphy. The patient did not admit the surreptitious taking of Levothyroxine and requested voluntary discharge. At discharge she was indicated treatment with cholestyramine and she was referred to a Mental Health consultation. The patient has not returned to our consultations.

Conclusion

In order to diagnose factitious thyrotoxicosis, a differential diagnosis must be made between several diseases that present with low iodine uptake on scintigraphy, such as subacute thyroiditis, iodine-induced hyperthyroidism, struma ovarii, and differentiated thyroid cancer metastases.