Is thyrotoxic periodic paralysis a disease caused by muscle membrane dysfunction?

INTRODUCTION: Thyrotoxic periodic paralysis (TPP) is characterized by recurrent episodes of reversible paralysis with hyperthyroidism. It is clinically similar to hypokalemic periodic paralysis (HOPP), which features significant ion-channel dysfunction and reduced muscle fiber conduction velocity (MFCV). However, the muscle membrane function in TPP is not known.

METHODS: For 13 patients with TPP and 15 age-matched controls, clinical assessment and serial neurophysiological testing, including nerve conduction, prolonged exercise (PE) testing, and MFCV. were performed.

RESULTS: MFCV values were elevated up to 1 year from the paralytic attack in TPP patients. In the group with a positive PE test, MFCV values were higher. There was no significant relationship between MFCV values and either hypokalemia or hyperthyroidism.

CONCLUSIONS: Although clinical manifestations in TPP are similar to those observed in HOPP, TPP appears to feature an alternate pathogenic mechanism. Specifically, MFCV values increased rather than decreased. Further studies are needed to support these findings. Muscle Nerve, 2016 Muscle Nerve 56: 780-786, 2017.