Autonomously functioning thyroid nodule associated with thyrotoxic periodic paralysis

Thyrotoxic periodic paralysis (TPP) is mainly associated with Graves' disease but rarely with autonomously functioning thyroid nodule (AFTN). We herein report a case of AFTN associated with TPP in which the latter resolved after (131) I therapy for the former. We analyzed the genes encoding thyrotropin receptor (TSHR), the alpha-subunit of the stimulatory G protein (Gsalpha), calcium channel CACNA1S and potassium channel KCNE3, and found that the patient does not carry the known mutations in these genes. Whereas the pathogenesis of TPP and AFTN remains to be understood, the present case suggests that ion channel defects responsible for familial hypokalemic periodic paralysis may not be associated with TPP, and that mutations in TSHR and Gs alpha genes may be less frequent in AFTN patients in the Japanese population.