In France it has been described under the name of stridulous laryngitis, because its dominant symptom consists in attacks of intense dyspnœa, during which the respiration is accompanied by whistling. Without making any attempt to prejudge the nature of the disease, which resembles the pseudo-diphtheritic forms of laryngitis in man, we prefer the term pseudo-membranous laryngitis. Moreover, this pseudo-membranous laryngitis very frequently accompanies pseudo-membranous sore throat, tracheitis and bronchitis, with formation of false membranes.
Causation. The causes suggested are similar to those of simple sore throat: they include chills, the ingestion of ice-cold water, or the inhalation of irritant gases, during outbreaks of fire, etc., etc.; but it is quite certain that here, as in many similar cases, a primarily simple laryngitis is complicated by a well-marked infection.
Symptoms. The general symptoms seen during the early stages consist in loss of appetite, general depression, rigors, and a rise in temperature of 1° to 2° Fahr.
Then, after twenty-four or forty-eight hours, the respiration becomes more rapid, difficult, whistling and dyspnœic, with intermittent attacks of suffocation.
Examination of the chest gives negative results, but, on the throat being manipulated, the slightest pressure exercised over the larynx produces attacks of coughing. During the first few days these attacks are loud, spasmodic, and difficult, but on succeeding days they lead to the discharge, from the nostrils or mouth, of masses of false membrane accompanied by whitish and sometimes blood-stained fluid. Secondarily the mucous membrane of the nasal fossæ appears inflamed to a varying degree. The conjunctiva is also affected, the eyes are watering. An important symptom consists in the fact that this watering is accompanied by internal ophthalmia, as in gangrenous coryza.
In consequence of the respiratory difficulty, the animal takes up a characteristic attitude, holding its neck stiffly in a horizontal position and its head completely extended; the nostrils are widely dilated. When the disease is fully-developed rumination is suppressed, the bowels are constipated and the fæces are coated as in grave cases of enteritis, the yield of milk diminishes, the heart beats feebly, the pulse remains small; death may occur from asphyxia, and probably also from intoxication.
The disease usually lasts from eight to ten days, but death may occur earlier. In the majority of cases, however, the animal can be saved. All the symptoms diminish, the temperature falls, rumination again appears and with it appetite, and the whole condition becomes normal. Many animals, however, remain thin and recover slowly; these are principally cases which have suffered from pseudo-membranous bronchitis.
Lesions. The lesions may be confined to the larynx, but may also invade neighbouring cavities. They consist in the formation of mucoalbuminous and fibrinous exudates, covering the mucous membrane in superposed layers, penetrating the epithelial stratum, and adhering so strongly to the corium that attempts to loosen them cause the deeper seated structures to bleed.
Diagnosis. The symptoms are sufficiently well marked to prevent any confusion arising except with gangrenous coryza, but in this case there is no ophthalmia lesion of the nasal cavities, cutaneous eruption, or eruption over the claws.
The prognosis is grave when the disease attacks debilitated or exhausted animals.