Overview of Laryngeal Disorders
Also see Laryngeal Hemiplegia in Horses.
Laryngitis, an inflammation of the mucosa or cartilages of the larynx, may result from upper respiratory tract infection or by direct irritation from inhalation of dust, smoke, or irritating gas; foreign bodies; or the trauma of intubation, excess vocalization, or injury from roping or restraint devices (in livestock). Laryngitis may accompany infectious tracheobronchitis and distemper in dogs; infectious rhinotracheitis and calicivirus infection in cats; infectious rhinotracheitis and calf diphtheria in cattle; strangles, herpesvirus 1 infection, viral arteritis, and infectious bronchitis in horses; Fusobacterium necrophorum or Trueperella pyogenes infections in sheep; and influenza in pigs.
Edema of the mucosa and submucosa is often an integral part of laryngitis and, if severe, the rima glottidis may be obstructed. Edema may also result from allergy, inhalation of irritants, or surgery in the area. Intubation for anesthesia, especially when attempted with inadequate induction or poor technique, is likely to provoke laryngeal edema. Brachycephalic and obese dogs, and dogs with laryngeal paralysis (see Laryngeal Paralysis) develop laryngeal edema and laryngitis through severe panting or respiratory effort during excitement or hyperthermia. In cattle, laryngeal edema has been seen in blackleg, urticaria, serum sickness, and anaphylaxis. In pigs, it may develop as a part of edema disease. In horses, cattle, and sheep, laryngeal edema may lead to arytenoid chondropathy.
Laryngeal chondropathy is a suppurative condition of the cartilage matrix that principally affects the arytenoid cartilages; it is believed to result from microbial infection, often as a sequela of inhalation of irritants or trauma to the area. In herbivores, trauma can occur when administering medications by bolus or drench or by ingestion of rough foodstuffs; in dogs, trauma can occur from sticks or foreign bodies. Laryngeal chondropathy is characterized by necrosis and ulceration of the laryngeal mucosa, over or just caudal to the vocal cords, and abscessation within the arytenoid cartilage. Initially, there is often acute laryngeal inflammation. Later, there is progressive enlargement of the cartilages that commonly results in a fixed upper airway obstruction with stertorous breathing and reduced exercise tolerance. Laryngeal chondropathy is seen in horses, sheep, and cattle, most often young males. There is a distinct breed predisposition in Texel sheep and Belgian Blue cattle. Laryngeal contact ulcers are common in young feedlot cattle and often result in necrotic laryngitis and chondropathy.
A cough is the principal sign of laryngitis when edema is slight and the deeper tissues of the larynx are not involved. It is harsh, dry, and short at first, but becomes soft and moist later and may be very painful. It can be induced by pressure on the larynx, exposure to cold or dusty air, swallowing coarse food or cold water, or attempts to administer medicines. Vocal changes may be evident, especially in small animals. Stridor may result from swelling and reduced motion of the arytenoid cartilages in laryngeal chondropathy. Halitosis and difficult, noisy breathing may be evident, and the animal may stand with its head lowered and mouth open. Swallowing is difficult and painful. Systemic signs are usually attributable to the primary disease, as in infectious bovine rhinotracheitis, in which temperatures of 105°F (40.5°C) may occur. Secondary systemic signs due to inappetance and dehydration rapidly become apparent. Death due to asphyxiation may occur, especially if the animal is exerted.
Edema of the larynx may develop within hours. It is characterized by increased inspiratory effort and stridor arising from the larynx. Respiratory rate may slow as the effort of breathing becomes exaggerated. Visible mucous membranes are cyanotic, the pulse rate is increased, and body temperature rises. Horses may sweat profusely. Dogs with obstructions of the conducting airways may show extreme disturbance of thermoregulation in hot weather; marked hyperthermia is not uncommon. Untreated animals with marked obstruction eventually collapse and often have signs of pulmonary edema.
A tentative diagnosis is based on the clinical signs, auscultation of the laryngeal region, and exacerbation of stridor by palpation of the larynx. Definitive diagnosis requires laryngoscopy. In conscious horses and cattle, this can be achieved with a flexible endoscope passed per nasum; in dogs and cats, anesthesia or analgesia usually is required. The history and signs usually permit rapid identification of the primary disease and the associated laryngeal involvement. Bilateral laryngeal paralysis, laryngeal abscess, pharyngeal trauma and cellulitis, and retropharyngeal abscesses or masses can cause similar signs.
In laryngeal obstruction, a tracheotomy tube should be placed immediately; if a tracheotomy is not possible, airway patency may be established by passage of a pliable tube through the glottis. Corticosteroids should be administered to reduce the obstructive effect of the inflammatory swellings. Concurrent administration of systemic antibiotics is also necessary. In cases in which corticosteroids cannot be used, NSAIDs can be given. Administration of diuretic drugs, eg, furosemide, may be indicated to resolve laryngeal edema and, if present, pulmonary edema. Identification and treatment of the primary disease is essential. Palliative procedures to speed recovery and give comfort include inhalation of humidified air; confinement in a warm, clean environment; feeding of soft or liquid foods; and avoidance of dust. The cough may be suppressed with antitussive preparations, and bacterial infections controlled with antibiotics or sulfonamides. Control of pain with judicious use of an analgesic, especially in cats, allows the animal to eat, and thus speeds recovery. Subtotal arytenoidectomy is an effective remedy for laryngeal chondropathy of horses, although a return to full athletic capacity in competitive horses is uncertain. Tracheolaryngostomies and permanent tracheostomies have been used successfully to salvage cattle and sheep with laryngeal chondropathy but carry significant anesthetic risk. A medical alternative for ruminants is prolonged antibiotic therapy, 14–21 days of parenteral lincomycin (5–10 mg/kg), plus initial, short-acting corticosteroids.