The time course of creatine kinase elevation following concentric needle EMG

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Abstract
The electromyographic (EMG) exam and creatine kinase (CK) are commonly used to evaluate patients with neuromuscular diseases. Prior studies have demonstrated minimal elevation of CK following monopolar needle examination, indicating that a false positive elevation does not occur in normal individuals. We studied the magnitude and time course of CK change resulting from concentric (CNEMG) and monopolar (MNEMG) needle EMG examination on healthy volunteers. CK increased in all subjects following CNEMG and MNEMG. Statistically significant mean CK elevations over baseline were observed at 4, 8, 12, and 24 hours for CNEMG and at 12 and 24 hours for both MNEMG. Maximum elevation occurred at 12 and 24 hours for both CNEMG (mean, 178% of baseline) and MNEMG (mean, 134% of baseline). CK returned to baseline by 48 to 72 hours. In 25–30% of subjects CK elevation significantly exceeded the normal range. The magnitude of CK elevation is greater and the time course more prolonged than previously reported. CK measurements should be avoided 4 to 48 hours following CNEMG because of the potential for false positive results. Measurements immediately after and at 72 hours are not affected by the CNEMG or MNEMG. The time course for CK change following MNEMG is similar to CNEMG, but the magnitude is less.