Sural and Radial Sensory Responses in Patients with Sensory Polyneuropathy.

INTRODUCTION The sural/radial nerve amplitude ratio (SRAR) is the quotient of the sensory nerve action potential (SNAP) amplitudes (Amp) of the sural and the superficial radial nerve. It has been hypothesized that this ratio can be used for the detection of early axonal loss, because the sural SNAP amplitude will decrease first, thereby also decreasing the SRAR value. OBJECTIVES To determine the sensitivity and specificity of SRAR, age-adjusted sural and radial SNAP Amp in the diagnosis of axonal sensory polyneuropathy in cancer patients. DESIGN Retrospective review. SETTING Comprehensive cancer center. PATIENTS One hundred and ninety one EMG reports from January 2001 to December 2005. METHODS The independent variable is the diagnosis of axonal sensory polyneuropathy in the EMG reports that is based on multiple tests. MAIN OUTCOME MEASUREMENTS We assessed the agreement between classifications of axonal sensory polyneuropathy made using the current 'gold standard' and the proposed method that is based on patients' age-adjusted radial and sural SNAP amplitude; an SRAR being above or below the normal value (0.21). RESULTS We found that the sensitivities for age-adjusted radial SNAP Amp, age-adjusted sural SNAP Amp, and SRAR were 33%, 64%, 56% respectively; the specificities were 85%, 70%, 77% respectively. CONCLUSIONS SRAR is neither the most sensitive, nor the most specific in the diagnosis of axonal sensory polyneuropathy.