A Case of Thyrotoxic Hypokalemic Periodic Paralysis with Typical Electromyographic Findings during Paralytic Attack and after Recovery

J Korean Assoc EMG Electrodiagn Med 2004;6(1):71-75.
Published online May 10, 2004.

Abstract

Thyrotoxic periodic paralysis is an uncommon illness characterized by recurrent episodes of flaccid paralysis of skeletal muscles, usually accompanied by hypokalemia. The underlying pathophysiology remains largely unexplained and controversial. Up to now there are many clinical studies of thyrotoxic periodic paralysis, but a few electrophysiologic studies were reported in Korea, especially during paralytic attack. We encountered a patient with thyrotoxic periodic paralysis and carried out EMG study during paralytic attack and after a remission and got the following results. 1) Sensory nerve conduction study showed normal SNAPs from all tested nerves. 2) Motor nerve conduction study showed normal onset latencies and conduction velocities but reduced amplitudes of CMAPs. 3) Needle EMG showed considerably decreased insertional activities, but no abnormal spontaneous activities at rest and on volition, low-amplitude, shortduration and polyphasic MUAPs and reduced interferential patterns. 4) After a remission all abnormal findings returned to normal values on nerve conduction and needle EMG studies.

Key Words: Thorotoxicosis, Periodic paralysis, Hypokalemia, Electromyography