Page 51 - Problem-Based Feline Medicine

4 – THE CAT WITH STRIDOR OR STERTOR 43

Pathogenesis lateralization) may be required (see Laryngeal
paralysis section).
The cat appears to be more prone to fibrosis and stricture
formation of the upper airway than is the dog. Trauma In emergency respiratory distress, temporary
from external penetrating wounds, aspirated foreign tracheostomy may be required below the stricture,
bodies, or from caustic chemical damage, or post- although this too can lead to future stricture
operative scarring can lead to excessive scar formation formation.
and stricture.
The narrowed lumen creates the airway resistance and Prognosis
stridor. A web of fibrosis may form across the larynx
Depends upon the nature and location of the stricture.
and is especially dangerous.
Clinical signs Prevention

Laryngeal stenosis causes a dynamic airflow limitation, At the time of laryngeal trauma or surgery, corticos-
resulting in inspiratory stridor and dyspnea. teroids may help diminish scar formation.
Stridor is worse with excitement or exercise.

Occasional stertor is evident.
LARYNGEAL PARALYSIS
Voice changes (absent or whisper-like meow), or
harsh purring sounds may be reported. Classical signs

● Inspiratory dyspnea and increased airway
Diagnosis
noise.
Diagnosis is based on clinical signs and history of prior ● Stertorous breathing (snoring).
laryngeal damage or surgery. ● Stridor (high-pitched whistling =
obstructive).
Laryngoscopic inspection under heavy sedation or
● Voice changes, absence of purring.
light anesthesia with a rigid laryngoscope and blade
reveals the stricture.
Low-dose ketamine (4–6 mg/kg IV), ketamine/ Pathogenesis
diazepam (3–5 mg/kg/0.1–0.2 mg/kg IV) or propofol
Exact pathomechanism is unclear in cats because of the
(4–6 mg/kg IV) allows visual inspection.
small numbers reported.
Differential diagnosis It may be congenital, although most cases appear in
middle-aged to older cats.
Other causes of fixed upper respiratory tract obstruc-
tion are considerations, but can usually be differenti- Peripheral neuropathies of recurrent laryngeal nerves
ated visually or on biopsy. They include the following: can cause laryngeal paralysis. In dogs they have been
● Oropharyngeal neoplasia (SCC, oral melanoma, associated with endocrinopathies (hypothyroidism –
nasopharyngeal polyp). but this is rare in cats), myasthenia gravis, immune-
● Laryngeal or tracheal neoplasia (intraluminal mediated or paraneoplastic peripheral neuropathies,
adenocarcinoma, extraluminal masses) or foreign but this association has not been documented in cats.
bodies.
Trauma, either to the recurrent laryngeal nerve (head,
cervical or thoracic trauma) or to the structure of the lar-
Treatment
ynx itself, can impair the laryngeal function. Temporary
Surgical intervention is generally required. or permanent damage to the recurrent laryngeal nerve
● Surgical resection of the stricture, if possible, is may occur following cervical surgery, for example fol-
indicated. Laryngeal tie-back surgery (arytenoid lowing thyroidectomy.