Design and evaluation of a portable smart-phone based peripheral neuropathy test platform

In this paper, we describe a novel portable test platform that can be used to test peripheral neuropathy either within a clinic or at home. The system, called the PeriVib, is comprised of (1) a small, custom vibration motor designed to apply a vibration stimulus to the toe with constant pressure to test sensation threshold, and (2) a custom smart-phone app that enables a patient to run a series of functional gait and balance tests. Vibration is applied by PeriVib in two separate modes. The first mode, ramp-up, starts at zero amplitude and increases to a maximum level while the patient indicates when they start feeling the pressure by lifting their finger off the touch-screen on the phone. The second mode, ramp-down, starts at a maximal intensity and decreases in intensity; the patient indicates when they stop feeling the vibration. The smart-phone app determines the patient's threshold by recording the vibration amplitude when they indicate the onset or loss of vibratory sensation, depending on the mode. In both modes, the measurement is repeated five times. In addition to controlling the vibration motor during the vibration test, the smart phone app also enables collection of gait and sway metrics through the use of the accelerometer and gyroscope sensors on the smartphone. The entire set of tests requires approximately 5 minutes to complete and can be done by a patient with minimal instructions from a clinician. In a cohort of 28 subjects with a history of chemotherapy-induced peripheral neuropathy, we compared the PeriVib performance with two established threshold sensing systems: (1) a Biothesiometer device and (2) a tuning fork. We found that the sensation threshold estimated by PeriVib correlated well with the Biothesiometer ($\mathrm{R}^{2}$ of 0.68) but less well with the tuning fork ($\mathrm{R}^{2}$ of 0.15). Functional gait and balance metrics did not correlate with peripheral neuropathy severity.