Detection of Single Muscle Fiber Movements (Fibrations) in SMA Type I by High Resolution Ultrasound

Introduction: Movements of a group of muscle fibers innervated by a single motor unit (fasciculations) are detected by clinical inspection, electromyography and ultrasound. Up to now movements of single muscle fibers are realized just by electromyography and can be called fibrillations. We tried to analyze single muscle fibers by a new ultrasound technique and that was when we saw movements of single muscle fibers. Method: We examined three infants with spinal muscular atrophy (SMA) type I and typical deletion in the survival motor neuron (SMN) gene and ten children with other neuromuscular diseases by means of a high resolution ultrasound system (HDI 5000 and 15–7MHz-Compact-Linear-Broadband-Scanhead from Advanced Technology Laboratories, Washington, USA). Results: We found only in the three infants with SMA type I the well-known rhythmic and synchronous movements of groups of muscle fibers (fasciculations) as well as a turmoil of arrhythmic and asynchronous twitches of single muscle fibers. Conclusions: By means of high resolution ultrasound it was possible to detect movements of even single muscle fibers. The turmoil of single muscle fibers was very impressive. But we do not think the term fibrillations is right. Fibril is the diminutive form of fiber and myofibrils are the contractile filaments of muscle fibers. That is why we suggest the term fibrations. This term is derived from fiber, because we are not able to see movements of myofibrils but rather of single muscle fibers by the new ultrasound technique. Acknowledgements: We thank the local group of the German Society for Patients with Muscle Diseases (Deutsche Gesellschaft für Muskelkranke e.V.) in Elmshorn for financial support and we thank the departments for gynecology and pediopathology of Kiel University Hospital for technical support.