The most consistent weakness in the previously reported cases was the lack of a complete and accurate neurological examination by the clinician. Where autopsy material has been available, there has been a lack of microscopic cell and filament counts in and about the brain-stem nuclei. As regards older reports, it is realized that facilities for doing accurate histological examinations were not as great as they are at the present time, especially in view of the greater number of stains and counterstains available to the present-day pathologist. Biopsy material and evaluation of the electrical responses of the facial nerves and muscles also were not obtained in the past.
The following facts are presented in an effort to establish an etiological trend:
1. If the condition is considered to be entirely neurological in origin, several discrepancies which arose in the examination of the cranial nerves must be explained.
a. In none of the examinations in the three cases here presented was there any sensory loss over the distribution of the cranial nerves.
b. The oculomotor-nerve involvement is consistently incomplete, with preservation of function of the medial rectus and absence of function of the remaining recti (superior and inferior) and of the inferior oblique.
c. The facial musculature offers a confusing picture, since in a peripheral type of unilateral facial-nerve paralysis the overlap innervation of the frontalis muscle preserves the function of the frontalis muscle on the involved side, whereas in the central type of lesion—that is, above the nucleus—this overlap innervation is obliterated and the entire face is paralyzed. In these cases of Möbius' syndrome, however, the upper quadrants of the face are always involved, either unilaterally or bilaterally and, if any facial expression remains, it is always in the lower quadrants. This would be impossible to explain on the basis of a neurological lesion.
d. The electrical examination, both galvanic and faradic, at the motor points of the facial nerves and muscles indicates definitely that the nerves are present and functioning. Stimulation of the main facial-nerve trunk in one case in which the facial musculature of the upper quadrant was functionless and that of the lower quadrant was voluntarily active resulted in contracture of the muscles in the lower quadrant only.
2. It is impossible to implicate a definite period of time as that when failure of development would hinder the development of both the cranial-nerve nuclei and the extremities. A correlation can be made, however, between the stem tissue of the extremities and the branchial musculature, both being of mesodermal origin, while the cranial-nerve nuclei are of ectodermal origin.
3. In the syndrome of facial diplegia, which consists of paralysis of the sixth and seventh nerves only, a small lesion of the brain stem can easily explain the clinical findings. In the Möbius syndrome, however, which often includes involvement simulating other cranial-nerve lesions, as well as the malformations of the extremities, the intracranial lesions would certainly have to be multiple, and many of them would have to be incomplete to explain satisfactorily the preserved sensory apparatus and the partial motor involvement.
4. The most important conclusion to be drawn from the information presented in this paper is based on the pathological reports. In none of these reports was there any evidence of normal muscle, degenerated muscle, or remnants of pre-existing muscle. In none of the previous autopsy reports which showed absence or degeneration of the cranialnerve nuclei was there any mention of the status of the facial musculature. For this reason, the author would agree with Lennon's explanation of the etiology, which assigns the condition to a mesenchymal defect,—that is, absence of muscles with secondary failure of development of the nerves and ultimate degeneration of the nuclei as a result of disuse.
One of the most important orthopaedic conditions of unknown etiology to be kept in mind in any theory on the etiology of the Möbius syndrome is that of arthrogryposis multiplex congenita. J. R. Moore has pointed out that the Möbius syndrome may be arthrogryposis which is limited to the facial musculature, both stemming from a primary mesenchymal defect. For this reason, if the opportunity should arise to perform an autopsy in either type of case, a thorough histological examination of the musculature, peripheral nerves, cord, and brain stem should be performed.
Certainly all the findings in these children can be more easily and scientifically explained by Lennon's theory than by a theory which would presuppose primary, multiple, complete, and incomplete nervous-system lesions.