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.