Before the membranous deposit takes place the surface is in a condition of catarrh. Round the membrane the mucous membrane is red and slightly swollen. Not always, however, is that so. Particularly, the epiglottis may be covered on its inferior surface with a solid membrane or be studded with tufts of membrane, without much or any hyperæmia. The same can be said of the larynx, which is supplied with but a scanty distribution of blood-vessels and a sufficient network of elastic fibres to counteract the dilatation of blood-vessels peculiar to the catarrhal and inflammatory processes.
In uncomplicated cases of membranous laryngitis the membrane is confined to the larynx. Dozens of years ago—viz. before 1858, when diphtheria began to settle amongst us, never, it appears, to give up its conquest again—that took place in most cases. But since that period we meet with few such simple cases. As a rule, the membrane makes its appearance in the pharynx first, from there to descend into the larynx, and not infrequently into the trachea and bronchi. In other—fortunately, but few—cases the membrane is formed in the bronchi and trachea first, and invades the larynx from below.
Other organs suffer but consecutively and from the results of impeded circulation only. Thus, in post-mortem examination hyperæmia of the brain, liver, and kidneys, and bronchitis, broncho-pneumonia, or pulmonary oedema, are met with. Only those cases of membranous laryngitis which are complicated with general diphtheria yield the additional changes of the latter.
ETIOLOGY.—Intense irritants will produce an irritation on mucous membranes. In the larynx the product is, according to the severity of the irritation, either a catarrhal or a phlegmonous or a croupous laryngitis. The irritating substances may be mechanical, chemical, or thermical. Heubner produced diphtheria of the bladder by cutting off, temporarily, the supply of circulation. Traumatic injury of the throat and larynx will soon show a croupous deposit. Caustic potassium, sulphuric acid, caustic ammonium, corrosive sublimate, arsenic, chlorine, or oxygen, applied to the trachea or larynx, produce croupous deposits.1 Inhalations of heat, smoke, and chlorine have the same effect. These, however, are not the usual causes of croup. Cold and moist air is a more common cause, mainly during a prevailing epidemic of diphtheria. In former times, which are unknown to the younger generation of physicians, when no such epidemics existed, the only form of diphtheria occurring now and then was the local laryngeal diphtheria called pseudo-membranous croup. It was then a rare disease, while at the present time it is of but too frequent occurrence. In my Treatise I have explained at some length the relations of the two (p. 128).
1 A. Jacobi, Treatise on Diphtheria, p. 111.
Age has some influence in its development. The disease is not frequent in the first year of life; between the second and seventh years almost all the cases are met with. There are families with what appears to be a general tendency to croupous laryngitis. It may return. Even tracheotomy has been performed twice on the same individual.2 It is contagious. In the same family, from a case of croup, either another case of laryngeal croup may originate or another form of diphtheria will develop in other members of the household. It is not so contagious, it is true, as generalized diphtheria must be, for the infecting surface is but small in uncomplicated membranous croup, and the membrane not so apt to macerate and be communicated. Boys appear to be affected more frequently than girls. But the previous constitution makes no difference.
2 Treatise, p. 27.
SYMPTOMS.—Membranous laryngitis begins sometimes with but slight symptoms of catarrh, sometimes without them. Nasal, pharyngeal, and laryngeal catarrh may precede it a few hours or a week, with or without fever and with a certain sensation of pain or uneasiness in the throat and a moderate amount of cough and hoarseness. This condition has been called the prodromal stage of membranous laryngitis, though it is just as natural to presume that the changes in the mucous membrane merely facilitated the deposit of false membrane. The latter is more apt to develop on a morbid than on a healthy mucous membrane. The membranous laryngitis proper dates from the time at which, with or without an elevation of temperature, a paroxysmal cough makes its appearance—first in long, afterward in shorter intervals—which is increased by a reclining posture, mental emotions, or deglutition. At an early period this cough, which is very labored and gives rise to dilatation of the veins about the neck and head, is complicated with hoarseness, which gradually increases into more or less complete aphonia. Respiration becomes audible, sibilant, with the character of increasing stenosis. Inspiration becomes long and drawn; expiration is loud; head thrown back; the scaleni, sterno-cleido-mastoid, and serrati muscles are over-exerted; above and below the clavicles and about the ensiform process deep recessions take place in the direction of the lungs, which are expanded with air, but incompletely; dyspnoea becomes the prominent symptom, and occasional attacks of suffocation render the situation very dangerous and exciting indeed. These sudden attacks of suffocation are due—besides the permanent narrowing of the larynx by the membranes, which gradually increase in thickness—to occasional deposits of mucus upon the abnormal surface of the larynx and vocal cords, by partly-loosened false membrane, which now and then become audible, yielding a flapping sound, by oedema in the neighborhood, and by secondary spasmodic contractions. They are mostly met with in the evening and night; there is often a slight remission in the morning, which rouses new hopes, which soon, however, prove unfounded. Meanwhile, the pulse becomes more frequent in proportion with the increase of dyspnoea, and finally irregular; the temperature rises but little, and usually only when the throat or other organs, which are in more intimate connection with the lymph circulation than the larynx, are participating in the exudative process; and the laryngeal sounds become so loud as to render the auscultation of the lungs impossible. The glands of the neck are not swollen when the process is confined to the larynx. Now and then small or larger, rarely cylindrical, pieces of false membranes are expectorated, with or without any amelioration of the condition. In this condition the patient may remain a few hours or a few days.
Then the dyspnoea will rise into orthopnoea; the anxious expression and bearing of the little patient—for the vast majority of the sufferers are children—becomes appalling to behold; cyanosis increases; the head is thrown back; the larynx makes violent excursions upward and downward; the abdominal muscles work in rivalry with those of the thorax and neck; the surface is bathed in perspiration; still, consciousness is retained by the unhappy little creature tossing about and fighting for breath, and in complete consciousness he is strangled to death. Now and then the carbonic-acid poisoning renders the pitiful sight a little less appalling to the powerless looker-on by giving rise to convulsions or anæsthesia and sopor, which finally terminate the most fearful sight, the like of which the most hardened man, the most experienced medical attendant, prays never to behold again.
Besides the brain symptoms just mentioned, but few other organs give rise to abnormal function. In the kidneys the stagnant circulation results in albuminuria—in the bronchi and lungs, in hyperæmia, inflammation, and oedema.