Mistaken diagnoses in continuous muscle fiber activity of peripheral nerve origin. The syndrome of continuous muscle fiber activity of peripheral nerve origin has manifestations that resemble those of many other more common neurologic disorders during childhood and infancy. This similarity often leads to misdiagnosis when an adequate index of suspicion is not entertained and a comprehensive electromyographic examination is not performed. Two affected patients from 1 family are reported to illustrate the type of diagnostic errors that were made before the establishment of the correct diagnosis. 