Reliability and Validity of a Point-of-Care Sural Nerve Conduction Device for Identification of Diabetic Neuropathy

Abstract

BackgroundConfirmation of diabetic sensorimotor polyneuropathy (DSP) relies on standard nerve conduction studies (NCS) performed in specialized clinics. We explored the utility of a point-of-care device (POCD) for DSP detection by nontechnical personnel and a validation of diagnostic thresholds with those observed in a normative database.Research Design and Methods44 subjects with type 1 and type 2 diabetes underwent standard NCS (reference method). Two nontechnical examiners measured sural nerve amplitude potential (SNAP) and conduction velocity (SNCV) using the POCD. Reliability was determined by intraclass correlation coefficients (ICC [2], [1]). Validity was determined by Bland-Altman analysis and receiver operating characteristic curves.ResultsThe 44 subjects (50% female) with mean age 56±18 years had mean SNAP and SNCV of 8.0±8.6 µV and 41.5±8.2 m/s using standard NCS and 8.0±8.2 µV and 49.9±11.1 m/s using the POCD. Intrarater reproducibility ICC values were 0.97 for SNAP and 0.94 for SNCV while interrater reproducibility values were 0.83 and 0.79, respectively. Mean bias of the POCD was −0.1±3.6 µV for SNAP and +8.4±6.4 m/s for SNCV. A SNAP of ≤6 µV had 88% sensitivity and 94% specificity for identifying age-and height-standardized reference NCS values, while a SNCV of ≤48 m/s had 94% specificity and 82% sensitivity. Abnormality in one or more of these thresholds was associated with 95% sensitivity and 71% specificity for identification of DSP according to electrophysiological criteria.ConclusionsThe POCD demonstrated excellent reliability and acceptable accuracy. Threshold values for DSP identification validated those of published POCD normative values. We emphasize the presence of measurement bias – particularly for SNCV – that requires adjustment of threshold values to reflect those of standard NCS.

NC-stat for the diagnosis of diabetic polyneuropathy

“…The novel NC-stat®/DPNCheck™ device consists of a single handheld unit which is placed on the lateral aspect of the patient's lower leg such that the two stimulation (stainless steel) probes contact the leg just posterior to the lateral malleolous whereas the disposable biosensor, which records the sural response, is at a fixed distance of 9.22 cm proximal to the stimulating probes at the opposite end of the device, contacting the patient's lower calf [7]. More specifically, the largest probe is placed halfway between Achilles tendon and the lateral malleolus over the anatomical position of the sural nerve (anterior to the Achilles tendon and posterior to the lateral malleolus).…”

“…Thereby, automatic correction for skin temperature is achieved, compensating for SNCV with a linear temperature compensation factor of 1 m/s per°C (with a reference temperature of 28°C) and preventing beginning of tests when ankle temperatures are below 23°C (in this case the test will stop with°C displayed on the screen) [7]. Compensation is not applied on SNAP due to the more restricted effect of temperature on this parameter [7]. On the opposite of the probes and biosensor, a display screen and a single button is found.…”

“…On the opposite of the probes and biosensor, a display screen and a single button is found. Once the button is pressed, test is initiated and orthodromical nerve stimulation (between 4 and 16 times within 10-20 s) occurs [7]. SNAP is measured peak to peak and SNCV is measured to the onset of the initial negative deflection [9].…”

“…Among these new diagnostic methods, NC-stat ®/DPNCheck™, a novel point-of-care, portable, noninvasive device for automated nerve conduction study (NCS), manufactured by NeuroMetrix Inc. (Waltham, MA) is very promising [7]. This apparatus is fully integrated, in contrast to an earlier alternate version (NC-stat® by the same manufacturer), which included a remote on-call information system that received, interpreted, and then transmitted to physician's office patient NCS data [7,8].…”

“…This apparatus is fully integrated, in contrast to an earlier alternate version (NC-stat® by the same manufacturer), which included a remote on-call information system that received, interpreted, and then transmitted to physician's office patient NCS data [7,8]. The new device is designated to report two conduction parameters, namely sural nerve conduction velocity (SNCV) (latency to the initial positive peak) measured in meters per second (m/s), and sural nerve amplitude potential (SNAP) (baseline to initial negative peak) measured in microvolts (μV) [7].…”