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The value of electromyography: Toward an evidence‐based use of electrodiagnostic testing

Electrodiagnostic tests (electromyography and nerve conduction study) have been used for decades to evaluate patients with suspected neuromuscular diseases. The testing characterizes the physiology and helps to localize the lesions. Most neuromuscular specialists would agree that these studies are invaluable in revealing the nature of the underlying disorders, often beyond what is possible on clinical examination alone. On the other hand, it is also recognized that these tests add to healthcare cost and are uncomfortable for patients. Moreover, performance of the tests and interpretation of results are dependent on the expertise of the personnel. In this era of heightened sensitivity toward cost-effectiveness, it is reasonable to critically assess the usefulness of electrodiagnostic testing. A number of studies over the past decade have addressed the utility of electromyography in different clinical settings. Previous studies investigated the electrodiagnostic results in patients with upper extremity symptoms, weakness, and suspected neuropathy. All reports concluded that electrodiagnostic testing is informative, and the results provide a new or unsuspected diagnosis in 31–43% of cases. The study published in this issue of Muscle & Nerve is the latest such study. It is also the first to focus on the inpatient setting. In a cohort of 98 hospitalized patients, the electrodiagnostic results were confirmatory of the initial clinical diagnosis in 53% of the cases, and they provided a new relevant diagnosis in 12.6%. The relatively high percentage of confirmatory diagnoses and low percentage of new diagnoses were perhaps a result of the referral pattern of the study population. The vast majority (94%) of the cases were referrals from the Neurology service, implying that these patients had already undergone significant subspecialty evaluation at the time of referral. Remarkably, only 3% of the electrodiagnostic studies were normal. This may reflect the underlying illnesses in this inpatient cohort, although it also raises the possibility that electrodiagnostic testing was underutilized and was requested only to assess the most severely affected patients. Skeptics may argue that finding a diagnosis is one thing, but showing that it changes practice and clinical outcome is another. The cited studies took care to observe that patient management was indeed altered by the electrodiagnostic findings. The findings frequently led to further testing or new treatments. This of course hardly comes as a surprise to most neuromuscular clinicians. Although the available studies were either retrospective or unblinded, and likely subject to bias, they have provided good indications that electrodiagnostic studies are useful under appropriate clinical settings. The aforementioned studies complement the various evidence-based reviews published by the American Association of Neuromuscular and Electrodiagnostic Medicine on the utility of electrodiagnostic testing in specific neuromuscular disorders. They also represent an important first step in bringing an evidence-based approach to the practice of electrodiagnostic medicine. The relative usefulness of electrodiagnostic testing varies according to the underlying disease and alternative means available for diagnosis. The decision on testing should be based on the suspected underlying disease. Further study under specific clinical settings is needed to determine when electrodiagnostic testing is likely to be helpful, as well as when testing should not be done.