Quantitative motor unit action potential analysis of supraspinatus, infraspinatus, deltoideus and biceps femoris muscles in adult Royal Dutch sport horses

Reasons for performing studyReference values for quantitative electromyography (QEMG) in shoulder and hindlimb muscles of horses are limited. ObjectivesTo determine normative data on QEMG analysis of supraspinatus (SS), infraspinatus (IS), deltoideus (DT) and biceps femoris (BF) muscles. Study designExperimental observational study and retrospective case series. MethodsSeven adult healthy Royal Dutch sport horses underwent quantitative motor unit action potential analysis of each muscle using commercial electromyography equipment. Measurements were made according to published methods. One-way ANOVA was used to compare quantitative motor unit action potential variables between muscles, with post hoc testing according to Bonferroni, with significance set at P<0.05. The QEMG and clinical information from horses with lower motor neuron disorders (n = 7) or myopathy (n = 4) were summarised retrospectively. ResultsThe 95% confidence intervals of duration, amplitude, phases, turns, area and size index of quantitative motor unit action potential were 8.7-10.4ms, 651-867V, 3.2-3.7, 3.7-4.7, 1054-1457Vms and 1.1-1.5 for SS, 9.6-11.0ms, 779-1082V, 3.3-3.7, 3.8-4.7, 1349-2204Vms and 1.4-1.9 for IS, 6.0-9.1ms, 370-691V, 2.9-3.7, 2.8-4.5, 380-1374Vms and 0.3-1.3 for DT and 5.7-7.8ms, 265-385V, 2.7-3.2, 2.6-3.1, 296-484Vms and 0.2-0.5 for BF, respectively. Mean duration, amplitude, number of phases and turns, area and size index were significantly (P<0.01) higher in SS and IS than in DT and BF muscles. In addition, 4 of 7 normal horses had >15% polyphasic motor unit action potentials in SS and IS muscles. ConclusionsDifferences between muscles should be taken into account when performing QEMG in order to be able to distinguish normal horses from horses with suspected neurogenic or myogenic disorders. These normal data provide the basis for objective QEMG assessment of shoulder and hindlimb muscles. Quantitative electromyography appears to be helpful in diagnosing neuropathies and discriminating these from myopathies.