Voluntary muscle testing and dynamometry in diagnosis of motor impairment in leprosy: a comparative study within the INFIR Cohort Study

[[[ Aim: ]]] To evaluate hand muscle weakness detected through dynamometry as an indicator for change in motor nerve function detected by Voluntary Muscle Testing (VMT) of ulnar and median nerves. [[[ Design: ]]] The research was carried out as part of the INFIR Cohort Study among 303 subjects newly diagnosed with MB leprosy in two centres in UP state, northern India. [[[ Methods: ]]] To assess grip strength, key pinch and pulp-to-pulp pinch we adapted the cuffs of adult and neonatal sphygmomanometers. The testing was carried out at diagnosis and at each visit during a 2-year follow-up. [[[ Results: ]]] 303 subjects with newly diagnosed MB leprosy were included in the study. We found statistically significant differences in grip strength, key pinch and pulp-to-pulp pinch between groups defined by ulnar VMT grades at time of diagnosis. There was also a statistically significant difference in hand grip between groups defined by median VMT at diagnosis. In each case, strength tended to reduce with increasing motor involvement. We explored reduction in grip strength, key pinch or pulp-to-pulp pinch as indicators of change in ulnar VMT during follow-up. A 25% reduction over two visits was the most effective indicator. Changes were also associated with marginal changes in motor and sensory nerve function, most commonly associated with Type I reactions. [[[ Conclusion: ]]] Dynamometry is recommended as an additional method that may be used to monitor changes in nerve function in leprosy, particularly in subjects with early motor impairment of the ulnar nerve.