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Abbreviations
CPAP

positive continuous upper airway pressure

CT

computed tomography

FeLV

feline leukemia virus

FIV

feline immunodeficiency virus

MAD

mandibular advancement devices

MJR-VHUP

The Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania

OSA

obstructive sleep apnea

A 3-year-old castrated male domestic shorthair cat was presented to the MJR-VHUP Internal Medicine service for a history of upper respiratory noise and episodic dyspnea since having been acquired as a kitten. The clinical signs had been progressive in frequency and severity over the 2 months before presentation and appeared to be worse at night. An intermittent cough was also reported. Previous diagnostic evaluation performed by the referring veterinarian included thoracic radiographs and an upper airway examination under sedation that disclosed no clinically relevant abnormalities. The cat was vaccinated, tested negative for feline immunodeficiency virus and feline leukemia virus by ELISA, and consumed a commercial cat food. Other medical history included a healed coccygeal vertebral fracture from an injury that had occurred as a kitten. The cat was receiving no medications at the time of presentation.

On physical examination, the cat was bright and alert with normal vital signs. A stertorous noise was heard on each inspiration, and also could be heard as a referred sound on thoracic auscultation. Decreased airflow was noted from both nares. Auscultation of the heart was within normal limits. No cough was elicited on palpation of the trachea. The cat was overweight with a body condition score of 7/9. Abdominal palpation revealed no abnormalities.

Results of hematology and serum biochemistry disclosed a mildly increased serum cholesterol concentration (297 mg/dL; reference, 96–249 mg/dL), but were otherwise unremarkable. Thoracic and cervical radiographs indicated a mild to moderate bronchial pulmonary pattern suggestive of lower airway disease, widening of the cranial mediastinum (most likely because of fat accumulation), and subjective evidence of narrowing of the caudal nasopharynx.

The cat was placed under general anesthesia for an oral examination, sterile endotracheal wash, computed tomography (CT) of the head, and retroflex rhinoscopy. No abnormalities in laryngeal function or mass lesions were identified on oropharyngeal examination. Cytology of the tracheal wash fluid disclosed histiocytic inflammation and hemosiderosis as well as squamous epithelial cells and extracellular bacteria.

Computed tomography of the head (Fig 1) showed no abnormalities of the nasal cavity. The caudal aspect of the nasopharynx appeared to taper abruptly on the sagittal reformatted images with no open airway connection to the common pharynx, but no obvious nasopharyngeal stricture could be identified on transverse images. When compared with other feline head CT studies, similar appearance of the pharynx on sagittal images was noted in several cats with no respiratory clinical signs. Therefore, this finding was interpreted as artifactual because of the presence of the endotracheal tube, or as the result of general anesthesia.

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Figure 1. Transverse (A) and sagittal (B) CT images. The dorsal and ventral borders of the nasopharynx are indicated with calipers. Note that the caudal nasopharynx appears patent on axial view, and appears to be tapering quickly in the caudal portion on sagittal view.

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On retroflex rhinoscopy, the caudal nasopharynx appeared collapsed. The rhinoscope could be passed rostral to the narrowing, and normal choanae could be identified. Balloon dilatation of the caudal nasopharynx was attempted with 9 and 12 mm vascular balloons sequentially. The caudal nasopharynx would open slightly with each ballooning, and eventually would collapse back down, but no bleeding or tissue trauma as evidence of successful dilatation were noted where the pharyngeal tissue was dilated. These findings were most consistent with pharyngeal collapse, as opposed to a stricture.

Six hours after recovering the cat from anesthesia, fluoroscopy of the pharynx was performed in right lateral recumbency. The cat appeared fully conscious at the time of this procedure. Dynamic collapse of the common pharynx and caudal nasopharynx was evident (Fig 2). During each inspiration, ventral deviation of the dorsal pharyngeal roof and dorsal deviation of the soft palate were observed, resulting in partial or complete airway obliteration. During expiration, the pharyngeal roof and soft palate returned to their original position. Fluoroscopy was performed on a clinically normal domestic shorthair cat as a comparison, and no collapse was identified during any phase of the respiratory cycle.

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Figure 2. Fluoroscopic images of the pharynx in right lateral recumbency on expiration (A) and inspiration (B). The dorsal and ventral borders of the common pharynx are indicated with arrows. Note the markedly reduced diameter of the common pharynx on inspiration compared with expiration.

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The cat was discharged with prednisolone (0.5 mg/kg PO q12) and amoxicillin/clavulanic acid (15 mg/kg PO q12). A weight loss protocol by decreasing caloric intake was recommended. Follow-up communication with the client last occurred 6 weeks after initial presentation. The owner reported that the coughing had been completely resolved since the start of corticosteroids and antibiotics, but the stertorous breathing and episodes of dyspnea were unchanged.

Pharyngeal collapse refers to partial or complete occlusion of the pharynx by inward movement of the pharyngeal walls during inspiration.[1] Pharyngeal collapse is a common condition in humans associated with obstructive sleep apnea (OSA). This syndrome is reported to affect as many as 24% of adult males and 9% of adult females in the United States[2] with 2–4% thought to have symptoms such as fatigue, impaired cognition, and decreased quality of life.[3] Pharyngeal collapse also has been reported in horses. In 1 study, 3 of 37 racing horses presented for poor performance were diagnosed with dynamic pharyngeal collapse by high-speed treadmill videoendoscopy.[4] We describe a domestic shorthair cat diagnosed with inspiratory collapse of the common pharynx and caudal nasopharynx.

This report describes dynamic inspiratory collapse of the common pharynx and caudal nasopharynx in a cat. The diagnosis was made by fluoroscopic imaging of the pharyngeal area in the conscious cat in lateral recumbency. Historic, radiographic, and rhinoscopic findings supported this diagnosis.

Pharyngeal collapse in humans typically is associated with OSA, and is defined as recurrent (>5 per hour) reductions or stoppages in breathing during sleep as a result of pharyngeal narrowing in the presence of ongoing respiratory efforts. Obesity has been identified as the main risk factor and increases in adipose tissue and neck circumference are strong predictors of the disease.[3]

Additional predisposing factors that are thought to have a genetic basis include certain facial features (including posteriorly placed mandible, inferiorly placed hyoid, narrowing of the lateral pharynx, tonsillar enlargement, uvular enlargement, and tongue enlargement) and familial history of OSA.[3, 5] One study implicated increasing age as a predisposing factor, although the finding of increasing parapharyngeal fat with age may explain this association. Aging also was found to be associated with decreased pharyngeal dilator muscle activity in response to negative airway pressure.[6]

The genioglossus muscle is the main dilator of the upper respiratory tract. It is controlled by the hypoglossal motor nucleus, which typically is stimulated as a reflex to negative airway pressure. Humans with OSA typically have increased genioglossus muscle activity when conscious to compensate for increased pharyngeal pressure. This dilatation reflex is decreased while sleeping, as it also is in healthy individuals.[3] The cat described in this report can be distinguished from humans with OSA in that its collapse occurred while fully conscious. The physiology of reflex pharyngeal dilatation in cats may be an interesting area for future investigation.

Treatment of pharyngeal collapse in humans with OSA often requires a multimodal approach. As obesity is almost always present, weight loss generally is the first suggestion for treatment. Success with weight loss alone rarely is achieved, and most physicians also will recommend positive continuous upper airway pressure (CPAP), which is achieved by wearing a nasal mask at night. This approach applies pressure to the upper airway to prevent collapse, but patient compliance often is problematic. Pharmacologic options include medroxyprogesterone acetate, almitrine, protriptyline, and theophylline, but these have demonstrated minimal efficacy. Mandibular advancement devices (MAD) have shown promising results, with 50% of people experiencing elimination of snoring and 90% showing clinically relevant reduction in snoring.[1]

Surgical correction is controversial, but can be considered in cases that are refractory to medical management. A medical evaluation consisting of rhinoscopy, cephalometry (radiographs of the skull), laryngoscopy, and nocturnal polysomnography (a sleep study evaluating neurologic, muscular, cardiac, and ocular electrical activity) is recommended for surgical planning.[2]

Surgical procedures that can be performed include nasal reconstruction, uvulopalatopharyngoplasty, uvulopalatal flap, laser-assisted uvulopalatoplasty, mandibular osteotomy with genioglossus advancement, hyoid myotomy suspension, laser midline glossectomy and lingualplasty, maxillomandibular advancement, radiofrequency ablation, adenotonsillectomy, tracheostomy, or maxillary distraction. Most surgeons perform their preferred surgeries in sequence, although some perform multiple surgeries simultaneously. Clinical improvement is variable and ranges from 40 to 80% in cases managed surgically.[2]

Although pharyngeal collapse has not been reported in cats, there are reports of nasopharyngeal stenosis. These cases often present with similar clinical signs, and can be amenable to balloon dilatation or nasopharyngeal stenting. However, balloon dilatation appears to be ineffective if the narrowing is not caused by fibrous tissue, and stenting is not advised for cats with very caudally located strictures (<1 cm rostral to the caudal edge of the soft palate). Caudally placed stents are reported to cause exaggerated swallowing and can interfere with the ability to swallow or vomit.[7] For this reason, stenting would not be advised for patients to correct collapse of the common pharynx.

In this cat, lower airway disease was suspected in addition to pharyngeal disease. This concern was the rationale for instituting corticosteroid therapy at the time of discharge. It is uncertain whether or not presumptive concurrent lower airway disease played a role in the development of pharyngeal collapse. Pharyngeal fluoroscopy in cats with lower airway disease and nasopharyngeal signs may be a useful diagnostic test to consider before procedures conducted under anesthesia such as CT or rhinoscopy.

In conclusion, collapse of the common pharynx should be considered as a differential diagnosis in cats with clinical signs of inspiratory noise attributable to nasopharyngeal obstruction. Diagnosis can be made in the conscious patient with fluoroscopy. The efficacy of weight loss as a treatment is unknown, and devices such as CPAP or MAD would be expected to be poorly tolerated in cats. Future studies evaluating surgical procedures to attenuate negative inspiratory pressure and the value of medical options in affected cats are warranted.

References

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  2. References
  • 1
    Rodriguez-Lozano FJ, Saez-Yuguero MR, Linares-Tovar E, Bermejo-Fenoll A. Sleep apnea and mandibular advancement device. Revision of the literature. Med Oral Patol Oral Cir Bucal 2008;13:E549E554.
  • 2
    Won CHJ, Li KK, Guilleminault C. Surgical treatment of obstructive sleep apnea. Proc Am Thorac Soc 2008;5:193199.
  • 3
    Campana L, Eckert DJ, Patel SR, Malhotra A. Pathophysiology and genetics of obstructive sleep apnoea. Indian J Med Res 2010;131:176187.
  • 4
    Dart AJ, Dowling BA, Hodgson DR, Rose RJ. Evaluation of high-speed treadmill videoendoscopy for diagnosis of upper respiratory tract dysfunction in horses. Aust Vet J 2001;79:109112.
  • 5
    Togeiro SMGP, Chaves CM, Palombini L, et al. Evaluation of the upper airway in obstructive sleep apnoea. Indian J Med Res 2010;131:230235.
  • 6
    Malhotra A, Huang Y, Fogel R, et al. Aging influences on pharyngeal anatomy and physiology: The predisposition to pharyngeal collapse. Am J Med 2006;119:72.e972.e14.
  • 7
    Berent AC, Weisse C, Todd K, et al. Use of a balloon-expandable metallic stent for treatment of nasopharyngeal stenosis in dogs and cats: Six cases (2005–2007). J Am Vet Med Assoc 2008;233:14321440.