Medición manual de potenciales de unidad motora «miopáticos»

Abstract

Objective To investigate in patients with myopathy the possible existence of motor unit action potentials (MUAPs) whose individual duration is below a normal limit, and therefore patients having a pathological and possibly myopathic significance. Material and method The individual duration of 20 MUAPs was measured in the tibialis anterior of 82 healthy subjects, using the MUAP with the shortest duration from each subject. The same measurement was obtained for 24 patients diagnosed of myopathy, in these cases, using the MUAPs with individual duration below the minimum value found in the healthy subjects. Results The minimum individual duration found in healthy subjects was 6.8 ms. Number of MUAPs of 6.7 ms or less found in tibialis anterior of subjects with myopathy: 17 (33% of the subjects with myopathy). The minimum durations were compared between both healthy and ill subjects, there being significant differences between both, considered as pathological and specifically myopathic in the case of the subjects with myopathy. Conclusions Given the probably pathological and specifically myopathic significance of the MUAPs below 6.8 ms found in the tibialis anterior of the subjects with myopathy, the term «myopathic» MUAP is proposed herein for this type of MUAPs. The use of this finding as a specific electromyographic criterion for the diagnosis of myopathies is also proposed.