Invited review: limitations in predicting pathologic abnormality of nerves from the EMG examination.

Although electromyography (EMG = nerve conduction and needle electromyographic examination) is among the most sensitive and reliable approaches to detect and even to characterize certain aspects of nerve disease, it is important for physicians to appreciate that EMG has limited value in (1) inferring symptoms and neuropathic deficit (particularly the overall deficit recorded by clinical neurologists), (2) inferring involvement of small-diameter fibers, (3) inferring underlying biochemical or other pathophysiologic derangement, (4) inferring the presence and type and pathologic alterations in single fibers or Schwann cells, or (5) inferring interstitial pathologic abnormality. For 1 and 2, an adequate neurologic history and examination is needed. For 2, quantitative sensory (QSE) and quantitative autonomic (QAE) examination and histologic study of nerve often are especially helpful. For 3, clinical evaluation and a variety of laboratory examinations are needed. For 4 and 5, clinical evaluation and/or pathologic study of nerve may be needed. Electromyography has deservedly gained considerable acceptance as a worthwhile evaluative procedure for the study of neuromuscular disease. For some purposes, however, it is of limited value and other evaluative procedures are more informative. In this review, I trace the history of some of the reasons for the popularity of EMG and highlight some of its limitations. The purpose is not to diminish EMG or to elevate the procedure of nerve biopsy, rather to provide a conceptual framework for how these techniques and the clinical and other laboratory examinations can be used together in the assessment and follow-up of neuropathy.