Automation Is No Substitute for Accuracy in Nerve Conduction Studies

Newswise — To the patient, automated nerve conduction studies (NCSs) may sound appealing because they are less invasive than needle electromyography (EMG). To the physician with no formal electrodiagnostic (EDX) training, the ability to perform an automated test in their office is convenient for patients and may generate additional revenue for their practice. A team of trained electrodiagnostic physicians from the Mayo Clinic set out to evaluate the accuracy of the NC-stat®, an automated NCS device, in patients experiencing unilateral leg symptoms as compared to standard EDX techniques and found that comfort and convenience are no substitute for accurate and quality diagnostic testing for patients.

Fifty patients were recruited who had been referred to a tertiary EDX laboratory for evaluation of unilateral leg symptoms, a common symptom for patients with possible lumbosacral radiculopathy (LSR). Twenty-five patients who experienced leg symptoms, but had no evidence of LSR on standard EDX were enrolled into group 1. Group 2 consisted of 25 patients with unilateral leg symptoms and evidence of LSR on standard EDX. After completing standard EDX, all 50 patients underwent automated NCS, utilizing the protocol recommended by the manufacturer. The computer generated reports were compared to the diagnoses generated by standard EDX.

Preliminary data showed that in group 1, more than 93% of subjects had findings suggestive of LSR on automated testing. Five patients with alternative diagnoses identified on standard EDX (including plexopathy and amyotrophic lateral sclerosis) were suggested to have LSR by automated testing. In group 2, only two cases showed perfect concordance of findings on standard EDX and automated testing. Notably, the automated device failed to identify a radiculopathy present on standard testing in three cases.

The NC-stat® device was found to have low specificity in the identification of LSR. The value of the device as a screening tool for LSR appears limited, as nearly every patient evaluated with automated testing demonstrated abnormalities that would likely be secondarily referred. According to the researcher, Dr. Kevin Schmidt of Mayo Clinic in Rochester, Minnesota, “The study results showed that this device over diagnoses LSR. Patients could potentially be unnecessarily treated if treatment was initiated based on these results, or a large majority would be referred for a secondary study. To add another expense that is not providing useful diagnostic screening information is probably not warranted, and more concerning is if surgical procedures are recommended based on these results alone.” The senior investigator on the study, Dr. Andrea Boon, noted that due to the high rate of false positive results identified with automated testing, a protocol modification was applied for, to include 25 normal subjects, with no history of leg symptoms who underwent both standard EDX including needle EMG, and automated testing. This group also showed an alarmingly high rate of false positive results, with 18 of 25 normal subjects being diagnosed with LSR on automated testing. Only one subject was found to have evidence of an old LSR on standard EDX.

The complete findings and results of this study are being presented at the American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) 56th Annual Meeting in San Diego, California, at the Manchester Grand Hyatt, October 7-10, 2009. With over 5000 members, the AANEM is the world’s largest organization dedicated to advancing neuromuscular, musculoskeletal, and electrodiagnostic medicine.