Impact of first-line treatment choice on long-term outcomes of hyperthyroid Graves’ disease patients with thyrotoxic periodic paralysis

Background: Thyrotoxic periodic paralysis (TPP) is a unique manifestation of Graves' disease. While it is uncommon in Asian, it is extremely rare in Caucasian patients (0.1-0.2%). Previous studies suggested that TPP indicate more severity of Graves' disease and definitive treatments should be used to prevent relapses. Aim: To describe clinical features and impact of first-line treatment on long-term outcomes of TPP patients. Method: A retrospective cohort study over 35 years (1985-2019) of TPP from Graves' disease patients was conducted. All cases were analyzed and their clinical courses were compared between those who received antithyroid drugs (ATD) versus radioactive iodine (RAI) as a primary treatment. None of them underwent surgery. Results: A total of 2964 hyperthyroid Graves' disease patients were treated and followed-up at least 3 months over the study period. TPP was identified in 63 cases (2.1%) of all patients. There were 60 males and only 3 females with age at presentation of 35.0 +/- 8.2 years. TPP was the first presentation of hyperthyroid Graves' disease in 82.5% of them. During the acute attack of TPP, all patients presented with bilateral lower limb flaccid weaknesses with median serum potassium of 2.1 mmol/L. No fatal TPP cases were found. RAI was selected as primary treatment in 27 patients (42.9%). Nearly all RAI-treated patients rendered hypothyroidism with the median RAI dose at 15 mCi. No patients who were in remission after RAI treatment developed recurrent attack of TPP. In the remaining 36 ATD-treated patients with mean follow-up time at 9.1 years, relapse was found in 10 patients (27.8%) after the drug discontinuation and 6 patients suffered recurrent TPP. Only 8 ATD-treated TPP patients (22.2%) went into remission. Conclusions: TPP is a rare complication of hyperthyroid Graves' disease. Definitive treatment with RAI or thyroidectomy should be employed to prevent relapse and further attacks of TPP.