Muscles alive: Ultrasound detects fibrillations

ObjectiveMuscle ultrasound is capable of visualizing muscle movements. Recent improvements in ultrasound technology have raised the question whether it is also possible to detect small-scale spontaneous muscle activity such as denervation. In this study we investigated the ability of dynamic muscle ultrasound to detect fibrillations.MethodsEight patients with fibrillations were measured simultaneously by ultrasound and EMG to verify which movements on ultrasound examination corresponded to fibrillation potentials on EMG. The temperature dependency of ultrasound detected fibrillations and the observer agreement was assessed in five healthy subjects with focal denervation induced by botulinum toxin.ResultsFibrillations appeared on ultrasound examination as small, irregularly oscillating movements within the muscle while the overall shape of the muscle remains undisturbed. Visibility of fibrillations with ultrasound decreased with lower temperatures, with a 32% decrease at 30 °C compared to 39 °C. The interobserver agreement was substantial with a kappa of 0.65 for experienced observers.ConclusionFibrillations could be visualized with ultrasound. Consistent results could be obtained from trained observers. Care has to be taken to ensure an optimal muscle temperature to avoid false negative results, especially in distal muscles.SignificanceVisualization of fibrillations by muscle ultrasound opens the way for a new diagnostic application of this technique.