Abstract
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. 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. Retrospective review. Comprehensive cancer center. One hundred and ninety one EMG reports from January 2001 to December 2005. The independent variable is the diagnosis of axonal sensory polyneuropathy in the EMG reports that is based on multiple tests. 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). 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. SRAR is neither the most sensitive, nor the most specific in the diagnosis of axonal sensory polyneuropathy.
Highlights
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
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
Since the sural and radial nerves are at low risk for compressive injury, the sural and radial SNAPs are especially useful in the electrodiagnosis of polyneuropathy
Summary
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. We utilized these previously established lower limits of the normal values (LLN) for sural and radial SNAP amplitudes and the age-independent value for SRAR to determine the sensitivity and specificity of these values. We compared these result to a commonlyused sural SNAP amplitude cutoff value of 5μV in the diagnosis of distal axonal sensory polyneuropathy in cancer patients
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