RESUMO
BACKGROUND: Resistance to thyroid hormone (RTH) is a rare condition characterized by elevation of thyroid stimulating hormone (TSH) and thyroid hormones (TH). Its association with Hashimoto's thyroiditis was described in 1993 and occurs in 1 of 1.3 million births. CLINICAL CASE: We present a female patient with a family history of hypothyroidism. The patient's condition began in 2008 with symptoms of hyperthyroidism, elevated triiodothyronine (T3), thyroxine (T4) and TSH levels. Thyroid scan showed hypermetabolic activity and she was positive for anti-peroxidase antibodies (anti-TPO). After administration of thiamazole, TSH increased. In 2009 she was diagnosed with clinical hypothyroidism, high levels of TSH, and normal T3 and T4 levels. Levothyroxine was prescribed but TSH increased and she presented clinical signs of hyperthyroidism. Patient abandoned treatment after 1 month. Her symptoms fluctuated among hyperthyroidism, euthyroidism and hypothyroidism. In 2010 she presented tachycardia, weight loss, and high T3, T4 and TSH levels. Thyrotropin-secreting adenoma (TSHoma) was suspected and ruled out by magnetic resonance imaging (MRI). Thyrotropin releasing hormone (TRH) test was performed. TSH increased and the α-subunit of pituitary hormones retained low levels. CONCLUSIONS: RTH diagnosis requires exclusion of a TSHoma because both present a similar pattern according to thyroid tests. The association between Hashimoto's thyroiditis and RTH is not well known. This pathological condition has a mutated TRß gene in 75% of the cases.
