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The value of electrodiagnostic studies in patients with suspected polyneuropathy

In the present day, there is an increasing emphasis on the value and appropriate use of medical resources, both diagnostically and therapeutically. Patients and insurers are more closely questioning whether their care, and the cost of their care, is indicated and necessary. Among these concerns is the use of electrodiagnostic (EDx) studies in patients with suspected peripheral polyneuropathy (PN). A Polyneuropathy Task Force formed from the American Academy of Neurology (AAN), American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM), and the American Academy of Physical Medicine and Rehabilitation (AAPMR) was assembled to develop a case definition of distal symmetric polyneuropathy. They reported the combination of neuropathic symptoms, signs, and EDx findings as accurate in the diagnosis of distal symmetric PN. However, their focus was to standardize and facilitate research and epidemiological studies. Expert opinion varies on the clinical value and utility of EDx studies for PN, with some advocating restricting its use to certain uncommon situations, and others questioning whether it impacts management in comparison to the clinic assessment alone. Consequently, the role of EDx studies in evaluation of PN remains unsettled and, at present, is not optimally addressed by existing practice parameters. The study by Ginsberg and Morren in this issue of the Journal has advanced our knowledge and understanding on the issue of the value of EDx studies for suspected polyneuropathy. The authors retrospectively analyzed 162 patients referred for EDx studies for the diagnosis of “peripheral polyneuropathy” at a large tertiary institution over a 1-year period. Only a third of patients were found to have PN on EDx studies and, of these patients, more than half had additional neuromuscular diagnoses. The remainder had normal studies or other diagnoses, the most common being entrapment neuropathies and radiculopathies. Patients referred by neurologists were slightly more likely to demonstrate a PN on EDx studies than those referred by non-neurologists. Thus, neurologists and neuromuscular specialists both had a substantial number of normal studies or studies with alternative electrophysiological diagnoses. Among the numerous variables analyzed, only age, length of symptoms, and male gender increased the yield (and then only slightly) of demonstrating a PN on EDx studies. A pure PN was only found in 14.2% of patients in their study, suggesting that, in 85.8% of cases, the referring physician obtained information that could not be ascertained by the clinical examination alone. Although their study did not specifically address change in management or outcome when performing EDx studies, it is a reasonable conclusion that a normal study that excluded a large-fiber PN, and/or demonstrated an alternative neuromuscular diagnosis, substantially influenced the subsequent evaluation and treatment of these patients. It is important to note that confirming the clinical suspicion also negates the need for further testing and expense. A normal study may point to other diagnoses, some neurological (eg, small-fiber neuropathy) and some non-neurological (eg, plantar fasciitis). Most importantly, an alternative EDx diagnosis could indicate a major difference in terms of outcome. It is important to add that the authors excluded patients referred specifically for demyelinating polyneuropathy, pure sensory polyneuropathy, and mononeuritis multiplex. As the confirmation of each of these conditions is associated with a limited differential diagnosis and, in many, specific treatment, the study likely underestimates the value of EDx studies in suspected PN. The Polyneuropathy Task Force of the AAN, AANEM, and AAPMR also developed two clinical practice parameters. The first provided recommendations for the role of laboratory and genetic tests in the evaluation of distal symmetric PN, and the second on the utility of autonomic testing, nerve biopsy, and skin biopsy. Although there was an acknowledgment that EDx studies are usually performed to confirm a PN, no specific consensus statement derived from evidence-based studies was made. The Ginsberg and Morren study now adds compelling new evidence of the importance and value of performing EDx studies in the evaluation of suspected PN.