Switching of Hashimoto Thyroiditis Into Graves’ Disease: A Case Report and Literature Review

Background: Hashimoto thyroiditis (HT) and Graves’ disease (GD) are autoimmune inflammatory thyroid disorders. The evolution from GD into HT is the most common scenario while the conversion from HT into GD seems to be less common. Case Presentation: A 20-year-old female patient referred to the endocrinology clinic with a three-month history of fatigue, lethargy, lack of appetite, constipation, menorrhagia, cold intolerance, and 5 kg weight gain in the last two months. Clinical examination showed dry skin, scalp hair loss, and painless hard goiter whereas thyroid ultrasound revealed generalized homogeneous hypoechoic thyroid hypertrophy. Laboratory tests demonstrated increased serum thyroid-stimulating hormone (TSH) 210 µIU/L (normal: 0.25-4.50), decreased free thyroxine (FT4) 0.37 ng/L (normal: 0.8-1.8) and free triiodothyronine (FT3) 1.94 pg/mL (normal: 1.8-4.6), and finally, increased thyroid peroxidase antibodies (anti-TPO) 462 IU/mL (normal: up to 34). Based on observations, HT was diagnosed and thus daily treatment with levothyroxine 75 mcg was started for the patient. Two months later, she referred with symptoms suggestive of hyperthyroidism with reduced TSH levels, which did not improve after levothyroxine cessation, thus more laboratory tests were conducted and revealed decreased TSH levels, increased T3 and T4, and TSH receptor stimulating antibody (TSAb)levels, and increased radioactive iodine uptake at 24 hours. Therefore, the diagnosis of GD was made. Five weeks after treatment, she was in full remission. Conclusion: Although the switch from HT into GD is rare, it can occur at any time during the disease. Nonetheless, early diagnosis and treatment would improve the quality of care.