Sural Radial Amplitude Ratio: A Study in Healthy Indian Subjects

CONTEXT: The amplitude ratio of sural radial sensory nerve action potential is used as a sensitive measure for the diagnosis of an early distal axonal peripheral neuropathy. There is no age-stratified reference data available. AIM: To establish age-stratified sural radial amplitude ratio (SRAR) reference data in healthy Indian subjects. STUDY SETTING AND DESIGN: The study was conducted in the electrodiagnostic laboratory of a tertiary city hospital and is an analytical, prospective, and field trial study. MATERIALS AND METHODS: A prospective study was conducted on 146 healthy volunteers between 18 and 86 years, stratified into 6 groups, a = 18–30 years, b = 31–40 years, c = 41–50 years, d = 51–60 years, e = 61–70 years, and f = >70 years. SURAL: Radial amplitude ratio was calculated. STATISTICAL METHODS: Stata 12.1 statistical program was used. Lower limit of SRAR was obtained (mean-2SD of transformed data). ANOVA defined the intergroup variability, and linear regression and Pearson's correlation assessed the statistical significance. RESULTS: The lower limit of normal SRAR, for each age group is as follows: a: 0.30, b: 0.23, c: 0.20, d: 0.17, e: 0.17, and f: 0.08. SRAR of groups a, b, c was significantly different from groups e and f. Similarly, SRAR was significantly different between groups d and f but not between groups d and e or a, b, c, d. CONCLUSION: This study provides age-stratified reference data for SRAR. There is evidence to suggest that SRAR varies with age; hence, a single value of SRAR should not be used when diagnosing a peripheral neuropathy based on this criterion.