Automated hand‐held nerve conduction devices: Raw data, raw interpretations

The use of automated hand-held nerve conduction devices is among the newest and most controversial topics in the field of electrodiagnostic (EDX) medicine. These systems use anatomically configured biosensors to perform and record nerve conduction studies. A hand-held device records the responses. The user can then transmit the data to the company where a computer software system analyzes it and automatically provides an ‘‘interpretation.’’ Sounds slick and easy, right? There is no question about it: it is slick, and it is easy. But is this method of electrodiagnosis accurate enough to replace the currently acceptable standard of diagnosis for patients with peripheral nerve lesions? Can it really replace a focused history, physical examination, and tailored EDX evaluation performed by a specialist in electrodiagnostic medicine? The NC-stat system, manufactured by NeuroMetrix (Waltham, Massachusetts), is one of the most prevalent of these hand-held devices. According to company documents (www.neurometrix.com), NC-stat is capable of reliably diagnosing a number of peripheral nerve problems, including lumbosacral radiculopathy and carpal tunnel syndrome. In a high-profile article in The New York Times, the chief executive of NeuroMetrix was quoted as saying, ‘‘We’ve put the technology in the hands of all physicians, allowing them to replicate the diagnostic accuracy of the specialist.’’ But how true is this? Let us review the evidence. The U.S. Food and Drug Administration (FDA) has approved marketing of the NC-stat as a ‘‘nerve conduction velocity measurement device’’ (www.neurometrix.com). The most recent FDA 510(k) Summary states that the NC-stat is ‘‘substantially equivalent to the TECA TD-10/TD-20 EMG and nerve conduction velocity measurement device.’’ What this means is that nerve conduction measurements obtained using the NC-stat are comparable to those obtained using conventional equipment. An electrical stimulus is delivered, and nerve or muscle compound action potentials are recorded. In other words, the NC-stat is ‘‘substantially equivalent’’ in an engineering sense to conventional equipment. However, neither diagnostic accuracy nor utility (outcomes) of devices are required by the FDA for 510(k) approval, only that the device is substantially equivalent to any other device approved prior to May 28, 1976. A successful 510(k) application means only that the device has received ‘‘clearance’’ for marketing, not that it is approved for use. For physicians and patients, however, knowing the diagnostic accuracy of a procedure is the most important part. For us, interpretation of the data and the formulation of an accurate diagnosis are paramount in determining the most appropriate treatment for our patients. It is in this arena that there are concerns about the usefulness of the hand-held devices. There are a few studies that support the usefulness of hand-held devices (i.e., NC-stat), but most of these have been industrysponsored studies with a possibility of significant biases. Only a few other independent studies have addressed the diagnostic accuracy of handheld devices. One study assessed the usefulness of the NCstat system as a screening tool for carpal tunnel syndrome (CTS) in 1695 workers. Median distal motor latencies (DMLs) obtained with the device were plotted on a frequency histogram using the 95th percentile as the upper limit of normal. These results were compared with the same data interpreted by the automated NC-stat system. The automated reporting system classified 587 workers as having either ‘‘borderline’’ (n 1⁄4 221) or definitely ‘‘prolonged’’ (n 1⁄4 366) DML, whereas the independent analysis indicated that only 81 were abnormal. Thus, the automated system significantly overdiagnosed carpal tunnel syndrome in an Correspondence to: J. D. England; e-mail: jengla@lsuhsc.edu