I investigated the facial muscles of a child with Moebius syndrome, and many patients with chronic facial paralysis with the help of ultrasound (paresis in part for more than 10 years). I could see that, despite the long period of paralysis still facial muscles were sonographically detectable. So, what mechanism prevents a complete atrophy of the muscles and is there a realistic potential for regeneration?
Facial paralysis in Moebius syndrome is the result of agenesis of the 6th and 7th cranial nerve nuclei in the brainstem. In other words, the peripheral nerves never develop, therefore, muscles are either permanently atrophic or fail to develop. I'm not sure what you are seeing sonographically, but I can tell you when I perform smile reanimation surgery on these children at 4-5 years of age there are no muscles present, only fat. Whether the facial muscles failed to develop or they underwent atrophy from early in development due to lack of innervation, I have never found any evidence of any target muscles to reinnervate. Also, whether it's Moebius syndrome or other source of paralysis greater than 2 years, the result is often permanent and irreversible atrophy due to loss of motor end plates. Muscles may be present in these other circumstances, but they are irreversibly atrophied.
Thanks for the answer!
In the child with "Moebius syndrome" we were able to clearly identify sonographically mimic muscles. The muscles were strong atrophied and the echo intensity was increased, but also muscular units were detectable. Similarly, (sonographically) strongly atrophied facial muscles we could identify in children with facial palsy. Even with such strongly atrophied muscles, we showed an increase in muscle size and decrease in echo intensity at Renervation.These results correlated with the clinical recovery.
So, is there a kind of incomplete form of Moebius Syndrome? With typical clinic but with facial muscles...?
Hi, Maik.
You should search in Pubmed something related to long term denervation in mammals. Years ago, Prof U Carraro, asked me to make some electrophysiology in very long term denervated rat muscles. If I remember well they were denervated since half or one year. Fibers were incredibly atrophied, but they sill have a (very poor) membrane potential, even if without any oscillation (the so called fops; see an old paper by Purves and Sakmann on J physiol, if I remember well) nor fibrillatory spontaneous action potentials (in fact membrane potential was highly depolarized). Recordings remained as a simple observation and they were not published.
I hope this could give you some information.
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