Periodic paralysis as a new phenotype of resistance to thyroid hormone syndrome in a Chinese male adult

Abstract

Context: A majority of patients with resistance to thyroid hormone (RTH) are asymptomatic, whereas some patients show signs of hyperthyroidism, or hypothyroidism, or both. Thyrotoxic periodic paralysis is the mostcommonform of acquired periodic paralysis. However, it has not been reported in a patient with RTH up to now. Objective: We evaluated a 36-year-old male patient from China with elevated serum free T4 and free T3 and inappropriately high TSH who presented with periodic paralysis. Study Design: Clinical, biochemical, and radiological assessments, as well asDNAsequencing, were performed. Results: The patient's laboratory tests revealed the following: TSH, 6.14 mIU/L (0.27-4.2 mIU/L); free T3, 12.85 pmol/L (2.8-7.1 pmol/L); free T4, 33.62 pmol/L (9.05-25.5 pmol/L); and serum SHBG, 19.4 nmol/L (18.3-54.1 nmol/L). No significant suppression of TSH was observed in the rapid TSH suppression test with somatostatin analogs. Compound muscle action potential after exercise of the patient was reduced by 58%. Sequencing of thyroid hormone receptor genes confirmed a C446S mutation in the THR gene. Conclusions: This is the first report of periodic paralysis as anewphenotype ofRTHsyndrome.