Figure 1.3 In the normal animal, palpation of the soft palate will readily depress tissue into the dorsal nasopharyngeal wall. The presence of a mass lesion in the nasopharynx will result in resistance to depression.

Neoplastic disease or cryptococcosis within the nasal cavity leads to ipsilateral mandibular lymph node involvement and the disease process can sometimes be identified by cytology of a lymph node aspirate, even when there is no palpable enlargement. Nasal aspergillosis can result in reactive lymphadenopathy, although no fungal elements will be found. Nasal depigmentation along the drainage path of nasal discharge is a relatively specific feature of canine nasal aspergillosis found in up to 40% of cases and is thought to result from elaboration of a dermonecrotic toxin by the fungus (see Chapter 4).

Loud Breathing

      Definition

      Loud breathing most commonly results from a disorder affecting the nasal cavity or upper airway (larynx, pharynx, or cervical trachea), although occasionally animals with lower airway disease will present for loud, audible breathing. Stertor and stridor are loud sounds resulting from narrowing of upper or large airways typically, and are often audible without a stethoscope, although subtle stridor can be missed without specific auscultation over the larynx. Importantly, some animals will suffer from both stertor and stridor, which can have important ramifications for documenting the extent and severity of the obstructive disease, as well as defining optimal treatment.

      Stertor is a discontinuous gurgling or snoring sound that is produced as air flows past a soft tissue obstruction in the upper airway. It can be caused by narrowing within the nasal cavity, by elongation or thickening of the soft palate, or by edema or eversion of laryngeal saccules. Tonsillar enlargement or mass lesions in the oral cavity can also lead to stertor. In brachycephalic dogs and cats, it is not possible to localize the source of stertor on physical examination alone and stertor is often multi‐factorial. Stertor varies in tone and pitch, and it can be audible on inspiration, expiration, or both.

      In contrast, stridor is classically an inspiratory noise of a single, high pitch that results from rapid flow of air past a rigid obstruction, such as a paralyzed or collapsed larynx. Stridor can also be heard in an animal with a laryngeal mass or occasionally in an animal with nasopharyngeal stenosis. It can also be ausculted in an animal with a fixed large airway obstruction due to stenosis, hypoplasia, compression, or a mass effect. The airway obstruction can be anywhere from the larynx to the cervical or intrathoracic trachea. In severe cases where a large mass is obstructing airflow, stridor can be present on both inspiration and expiration. Finally, cervical tracheal collapse can also result in stridor typically on inspiration.

      Epiglottic retroversion is a cause of intermittent airway obstruction in dogs in which respiratory distress is present in conjunction with stridor or stertor. Although rarely reported, it is increasingly recognized as a cause of serious clinical disease (see Chapter 5).

      Signalment

      Stertor is commonly encountered in brachycephalic dog breeds such as bulldogs (English and French), Pugs, and Boston Terriers, and is also seen in Himalayan and Persian cats. Loud breathing is often present early in life and becomes worse with the development of additional respiratory disease or with weight gain. Some animals are not presented for evaluation of stertor and respiratory difficulty until late in life because of the perception that noisy respiration is “normal” for the breed.

Animals with stridor due to congenital laryngeal paralysis are usually young (6–12 weeks) when the clinical signs are first apparent, although some breeds show signs at 4–6 months and others at 1–2 years of age. Affected breeds include the Dalmatian, Rottweiler, Great Pyrenees, Bouvier des Flandres, Siberian Husky, White German Shepherd, and some cats (see Chapter 5). Acquired laryngeal paralysis is most commonly found in older large breed dogs such as Labrador and Golden Retrievers as part of a generalized polyneuropathy. Brachycephalic breed dogs that develop laryngeal collapse are usually older at the time of diagnosis; however, because this is an end‐stage manifestation of airway obstruction, the age at which the condition is recognized varies depending on the severity of the obstruction.

      Physical Examination

In a normal animal, breathing is quiet at rest. Stertor and stridor can be heard without the use of a stethoscope; however, in some instances, careful auscultation over the neck region is needed to confirm stridor. Increasing respiratory flow rate by gentle exercise can improve detection of stridor; however, panting must be discouraged. In the normal animal, auscultation over the larynx and trachea will reveal loud, hollow sounds that are heard equally on inspiration and expiration. Because upper respiratory noises are typically loud and can obscure lung sounds, auscultation of the larynx and tracheal region is recommended in all patients prior to thoracic auscultation to improve differentiation of upper from lower respiratory sounds, as well as to enhance detection of heart sounds and murmurs. This is particularly helpful in brachycephalic breeds (Figure 1.4).