Reference values for nerve function assessments among a study population in northern India - I: Vibration perception thresholds

Objective: This paper presents normal reference values for vibration perception thresholds for a study population in northern India. The work was in preparation for the INFIR Cohort Study, a prospective study of people newly diagnosed with multibacillary leprosy which sought to identify early changes in nerve function predictive of new onset impairment and reactions. To establish the limits of normal function we collected data on subjects with no known neurological condition and computed the reference values defining the limits of normal function. Methods: Data on vibration perception in 5 bilateral nerves was collected from 362 healthy subjects stratified by sex and by age and drawn from the same general population as the subsequent leprosy-affected cohort. Reference values were computed from log-transformed data after the exclusion of outliers. Results: Normal reference values are presented in the form of 95 th percentiles for vibration perception thresholds among normal subjects for 5 peripheral nerves within 8 age and sex groupings and by centre. The reference values are compared with those published for other populations. The incidence of impairment at diagnosis among the leprosy-affected cohort is described and illustrated.