How to interpret normal electromyographic findings in patients with an alleged history of polio.

OBJECTIVE In some patients with a history of polio, the electromyography is normal, not showing the typical neurogenic signs. The aim of this study was to explain the normal findings in electromyography, especially in paralytic polio. DESIGN Retrospective study. SUBJECTS/METHODS Concentric needle electromyography, macro electromyography (including single fibre electromyography) and neurography were performed in various combinations in 688 patients with an alleged history of polio. RESULTS Thirty-five patients with paralytic polio had normal or minimally abnormal neurophysiology. In 6 patients the diagnosis of polio was rejected and was instead found to be other diagnoses. Three patients had a very atypical history. Of the 26 with possible paralytic polio, 17 showed a strong suspicion of previous paralytic polio without any neurophysiological signs of degeneration of the anterior horn cells. CONCLUSION If neurophysiological findings are normal in patients with a history of polio, the original diagnosis may be incorrect. However, the absence of electromyography changes does not entirely exclude a previous history of polio with transient functional loss without degeneration of anterior horn cells vulnerable for later functional impairment.