Paralysis of the External Tensors of the Cords.
This is a rare disease, but is present in complete paralysis of the superior laryngeal nerve. It is then associated with anæsthesia of the superior portion of the glottis, as well as paresis of the depressors of the epiglottis, and generally of the constrictors of the vestibule of the larynx.
ETIOLOGY.—It may be the result of injury to the external branch of the superior laryngeal in its distribution to the muscles. It may be caused by diphtheria. It is possible that the motor fibres of the superior laryngeal nerve may be alone involved, while the sensitive portion is still normal. Cases of partial paralysis are recorded by Von Ziemssen, Gerhardt, and others.
The SYMPTOMS are such as we should expect in diminished tension of the vocal bands: lowering of the pitch of the voice, with inability to reach the higher notes. There ought to be, therefore, hoarseness. Acute paralysis of this muscle has been known to produce aphonia (Ramon).
DIAGNOSIS.—It is said that this form of paralysis gives rise to a well-recognized condition which may be seen in the laryngeal mirror. The cords are described as wavy, irregular in their relation to each other, like the position of two pieces of ribbon, which, having an attachment at their extremities near to each other, are allowed to fall into folds. This condition, if ever present, is, I am convinced, very rare. It is probable that the descriptions have been given to correspond with what ought to be seen, rather than what is actually seen, in the mirror. There is said to be a slight depression of the vocal processes in the act of inspiration, and a corresponding elevation of them in the act of expiration and phonation. The diminished tension should produce this change in position. The disease may also be recognized by placing the finger upon the edge of the crico-thyroid muscle during the effort to speak. The muscle acts so strongly in the healthy condition that it may be easily felt; in paralysis this contraction is wanting.
The course and duration of the disease must depend upon the cause and complications. When the muscles suffer in common with the sensory apparatus supplied by the superior laryngeal nerve, as in the case of diphtheria, there is reason to expect that it will disappear with the other morbid phenomena.
Paralysis of the Posterior Crico-Arytenoids.
The functions of these muscles render any loss of their power as glottis-openers a matter of importance. It will be remembered that they are so situated that they not only rotate the arytenoids, turning the vocal processes away from each other, but they also serve to fix the cartilages, giving them a firm support as points of attachment for the vocal cords. The outer fibres tend also to draw the body of the arytenoids away from each other, as well as to fix them in a postero-lateral position. They are, more than any other of the muscles of the larynx, organs of respiration. They are also in constant action: with each inspiration they contract, and during expiration they fall into rest. In this respect they resemble the other muscles of respiration and the central organ of the circulation. In some respects they also resemble the muscles of the heart in the degenerative changes to which they are subject. Their antagonists are the lateral crico-arytenoids. When both sets of muscles are paralyzed, the glottis is in what is known as the cadaveric condition; that is, the vocal cords are neither widely separated nor parallel to each other. There is an opening of a triangular shape as in the act of easy inspiration, not sufficiently approximated to admit of speech, but sufficiently open to admit of free inspiration. With this understanding of the physiology of the parts, we can readily appreciate the results of the loss of power of these muscles. As stated by Bosworth, the especial danger is in the integrity of the adductors, tending for the want of antagonism to keep the glottis closed. Of all the muscles of the larynx, these are therefore the most important so far as life is concerned.
The disease is progressive (Lefferts, Semon, Bosworth).
The first symptom which attracts attention is generally inspiratory dyspnoea while taking active exercise. The difficulty continues to increase till there is constant difficulty in the act of inspiration, usually with spasm. The dyspnoea is more marked during sleep than when awake. Death may occur at this period of the disease before the gravity of the trouble has been recognized. As a rule, tracheotomy will be required to prolong life, after which the dangers to the patient are passed.