What is the role of nerve conduction studies in the workup of periodic paralyses (PP)?

Updated: Apr 30, 2018
  • Author: Naganand Sripathi, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

The compound muscle action potential (CMAP) amplitude declines during the paralytic attack, more so in hypokalemic periodic paralysis. Sensory nerve conduction study findings are normal in most patients with periodic paralyses. Nerve conduction findings may be abnormal when the patient has peripheral neuropathy associated with thyrotoxicosis.

Repetitive nerve stimulation in hyperkalemic periodic paralysis may show a decrement in CMAP (accentuated by cooling) that is steadily progressive without tendency to recover as in myasthenia gravis. The amount of decrement is variable and increases with increased frequency of stimulation. In some patients, it is seen only with stimulation greater than 25 Hz. [14]


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