We prospectively investigated the diagnostic accuracy and potential pitfalls of dynamic muscle ultrasound in the detection of fibrillations. The presence of fibrillations on both electromyography (EMG) and ultrasound was evaluated in 102 muscles of 38 patients with suspected fibrillation potentials, based on history and physical examination. Sensitivity and specificity were calculated. False-positive and false-negative results are described to identify pitfalls. Ultrasound detected fibrillations with a sensitivity of 45% and a specificity of 66%. Specificity improved to 85% when measurements were evaluated online. Proximal muscles showed higher sensitivities (63%) than distal muscles (33%). Ultrasound currently has a poor sensitivity and moderate specificity for detecting fibrillations. Several pitfalls were identified that, when avoided, could help improve diagnostic accuracy. Ensuring a distal limb temperature of at least 34°C and identifying external movement artifacts as well as voluntary contractions can improve efficacy and open the way for diagnostic application of this technique.
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