Upper respiratory tract obstruction is a life-threatening condition in animals. Rapid assessment of respiratory impairment and treatment is crucial. The possible causes of upper respiratory tract obstruction in cats include pharyngeal polyps, laryngospasm, laryngeal or pharyngeal trauma, tracheal or laryngeal foreign body penetration, and neoplasia of the trachea or larynx (8). When diseases of the laryngeal movement cause respiratory distress, the characteristic “stridor” breathing sound can be confirmed (9). Tumors, granulomas, or foreign bodies at the level of the larynx can lead to obstruction, and dyspnea can occur even when there is a functional problem such as laryngeal paralysis. However, severe edema due to inflammatory laryngeal diseases rarely causes obstruction (1,8,10). It can be life-threatening in case of upper airway obstruction when general antibiotics or anti-inflammatory medication is insufficient to relieve inflammation. Differentiation of these diseases is important for fundamental treatment. Rapid triage and emergent treatment are also important for the prognosis of cats that come to the hospital for upper respiratory dyspnea.

Here, we report an emergency case of a cat with upper airway obstruction due to inflammatory laryngitis, which is rare.

A 5-year-old neutered male domestic short-haired cat presented with acute dyspnea for 2 days, accompanied by lethargy, anorexia, and fever. The cat lived in a multi-cat environment and had no history of vaccination. No prior events that could affect the respiratory tract, such as general anesthesia via endotracheal tube intubation and trauma, were found.

Immediate stabilization with oxygen supplementation was initiated as emergency treatment. Physical examination revealed open-mouth breathing and stridor, which are upper respiratory distress patterns. Other examinations, including vital signs, hydration status, and lung parenchymal and cardiac auscultation, were unremarkable. Differential diagnoses for laryngeal disease were made as follows: polyps (nasopharyngeal), acute laryngitis or obstructive laryngitis, laryngeal trauma, foreign body, and neoplasia as major structural abnormalities and laryngeal paralysis in neuromuscular disease or paraneoplastic syndrome as a functional abnormality.

In a direct visualization via laryngoscopy under light anesthesia (midazolam 0.1 mg/kg intravenously [IV], Bukwang pharm., Seoul, Korea; alfaxalone 5 mg/kg IV, Alfaxan^®, Jurox, Rutherford, Australia), diffuse laryngeal swelling, especially severe thickening and swelling of the vocal folds bilaterally, was observed (Fig. 1A). Laryngeal movement according to the respiration phase was weakly identified, and the upper respiratory tract was almost obstructed with an extremely narrow lumen due to severe edema. No discrete mass suspected to be a polyp or neoplasia was identified, and there was no evidence of trauma or foreign bodies. As an urgent treatment, a temporary tracheostomy tube placement (all-silicone tracheostomy tube with a high-volume low-pressure cuff; Sewoon Medical, Cheonan, Korea) was performed immediately while the diagnostic procedure. Laryngeal ultrasonography showed circumferential thickening and hyperechoic changes in laryngeal-level soft tissue, including arytenoid, thyroid, and cricoid cartilage (Fig. 2A). Mild enlargement and rim enhancement of the bilateral tonsils were also identified on computed tomography (CT), which were considered inflammatory changes and not neoplastic lesions (Fig. 3). Bilateral retropharyngeal lymph node enlargement was also considered secondary reactive lymphadenopathy due to regional inflammation. No clearly demarcated masses (i.e., polyps or neoplasia) were identified in the larynx.

Figure 1. Direct visualization of the larynx. (A) Diffuse laryngeal swelling (asterisk) and hypervascularization (arrow head) on admission, (B) recovery from the obstructive laryngitis on day 17.

Figure 2. Ultrasonography of the larynx (A) and FNA cytology (B). (A) Hyperechoic changes (asterisk) in the soft tissue located on the right side of the trachea at the laryngeal level. (B) Laryngeal fine needle aspirates obtained under ultrasound guidance show predominant infiltration of neutrophils and mature squamous epithelial cells, and some of the neutrophils show degenerative changes. Mild dysplastic changes are observed in mature squamous epithelial cells, which are presumed to be inflammatory changes (200×, Diff-Quik stain).

Figure 3. Circumferential thickening of the laryngeal soft tissue around the arytenoid, thyroid, and cricoid cartilages (asterisk) (A), heterogenous contrast enhancement of the larynx (asterisk) (B), and bilaterally enlarged retropharyngeal lymph nodes (arrow head, C).

Ultrasound-guided aspirated cytological evaluation from the larynx showed predominant infiltration of neutrophils and mature squamous epithelial cells, and some of the neutrophils showed degenerative changes. Mild dysplastic changes were observed in the mature squamous epithelial cells, which were presumed to be inflammatory changes (Fig. 2B). No cellular malignancy, pathogens, or phagocytosed inflammatory cells were identified. Acute laryngitis was highly suspected; however, confirmative biopsy for histopathology was not performed per the owner’s request.

To evaluate the infectious causes accounting for the largest proportion of secondary causes of feline laryngitis, an upper respiratory disease polymerase chain reaction (PCR) test (Upper Respiratory Disease Real PCRTM Panel-Feline; IDEXX, Westbrook, ME, USA) was performed: M. felis was confirmed from the laryngeal surface swab; however, other pathogens for feline upper respiratory disease complex, such as feline herpesvirus 1, calicivirus, and Chlamydia felis, were not found.

Systemic inflammation was also confirmed by laboratory tests: complete blood count and blood film analysis revealed monocytosis (2.2 × 10³/μL; reference range, 0.05-0.67 × 10³/μL) and neutrophilia (29.02 × 10³/μL; reference range, 1.48-10.29 × 10³/μL) with left shift (2,764 band neutrophils/μL) and toxic changes. However, immunocompromised diseases, such as feline leukemia virus/feline immunodeficiency virus, had not been confirmed (SNAP feline triple test; IDEXX). Serum chemistry (Table 1) and an abdominal ultrasound showed no remarkable findings.

Table 1 . Changes in laboratory results associated with systemic inflammation in this cat.

Parameters	Reference interval	Results
		On admission	After discharge
White blood cells (×103/μL)	2.87-17.02	34.55	13.85
Neutrophils (×103/μL)	1.48-10.29	29.02	10.80
Monocytes (×103/μL)	0.05-0.67	2.19	0.42
Lymphocytes (×103/μL)	0.92-6.88	0.23	1.66
Band neutrophils (×103/μL)	0-1.0	2.8	0.6
Red blood cells (×103/μL)	6.54-12.2	6.25	8.03
Hematocrit (%)	30.3-52.3	30.2	37.5
Platelet (×103/μL)	151-600	109	220
Glucose (mg/dL)	74-159	192	n/a
Creatinine (mg/dL)	0.8-2.4	0.8	n/a
Blood urea nitrogen (mg/dL)	16-36	12	n/a
Phosphorus-Inorganic (mg/dL)	3.1-7.5	2.9	n/a
Calcium (mg/dL)	7.8-11.3	9.1	n/a
Total protein (g/dL)	5.7-8.9	7.7	n/a
Albumin (g/dL)	2.2-4.0	2.8	n/a
Globulin (g/dL)	2.8-5.1	4.9	n/a
Alanine aminotransferase (U/L)	12-130	20	n/a
Alkaline phosphatase (U/L)	14-111	10	n/a
Gamma-glutamyl transferase (U/L)	0-4.0	0	n/a
Total bilirubin (mg/dL)	0-0.9	0.3	n/a
Total cholesterol (mg/dL)	65-225	134	n/a
Amylase (U/L)	500-1,500	2,034	n/a
Lipase (U/L)	100-1,400	1,235	n/a

n/a, not available..

After the diagnosis of acute obstructive laryngitis, thorough tracheostomy tube management was performed, and methylprednisolone sodium succinate 5 mg/kg IV q 8 hours (Methysol^®, Alvogen Korea, Seoul, Korea), prednisolone (Solondo Tab^®, YuHan Corp., Seoul, Korea), and amoxicillin–clavulanate 12.5 mg/kg orally q 12 hours (Clavamox^®, Zoetis, Kalamazoo, U.S.A.) were administered to relieve edema and inflammation in the larynx for 10 days. To protect the tracheal mucosa from drying out and maintain moisture, nebulization, hydration, and irrigation were performed in the tube every 4-6 hours. The tracheostomy tube was replaced with a new one every 1-2 days. Butorphanol 0.3 mg/kg IV q 8 hours (Butophan^®, Myungmoon Pharm., Seoul, Korea) was administered for analgesia and sedation, and the gastrointestinal low-fat liquid was fed through a nasoesophageal tube. For long-term treatment, the route of prednisolone administration was changed to oral, and antibiotics were changed to doxycycline 5 mg/kg orally q 12 hours (Doxycycline Tab^®, Youngpoong, Seoul, Korea) and azithromycin 5 mg/kg orally q 12 hours (Zithromax^®, Pfizer Inc., New York, USA) 10 days after diagnosis, and administered for another week. Ten days after tracheostomy, when visually observed under light sedation, edema in the larynx was remarkably improved. On day 17, the motility of the vocal cords and arytenoid cartilage according to respiration was clearly identified (Fig. 1B), and the tracheostomy tube was removed. Clinical signs also improved, with the disappearance of edema and inflammation.

Upper respiratory tract obstruction in cats mainly originates from the nasal cavity and nasopharyngeal, pharyngeal, and laryngeal regions. Inflammatory laryngitis is uncommon; approximately 40 cases of inflammatory laryngeal disease were reported between 1991 and 2011 (5). Moreover, obstructive laryngitis had been rarely reported: only 5 cases in 18 years from a multicenter study (7); 5 cats over 9 years (1), and 3 cats in review articles (3,8) were described.

Airway obstruction due to inflammatory laryngeal disease is rare, and in the case of mild clinical signs, both the owners and the clinicians can overlook the existence of laryngeal disease and the possibility of acute progression. Therefore, an accurate diagnostic approach is important when laryngeal abnormality is suspected in cats with respiratory distress. A definitive diagnosis of obstruction of the larynx is possible by identifying structural and functional abnormalities in the larynx through direct visualization. Biopsy and histopathology are required for different diseases that cause structural abnormalities, such as laryngeal inflammation and tumors. In this cat, edema and hypervascularization of the entire laryngeal tissue and vocal folds were observed on gross examination, and the lumen was completely obstructed. Therefore, it was not possible to clearly differentiate between inflammatory laryngeal disease and laryngeal paralysis using only visual and imaging examinations because the motility of the larynx was not identified. However, the response to antibiotics and anti-inflammatory drugs was good, edema was relieved, and the motility of the larynx according to the respiratory cycle was confirmed. The cat completely recovered without recurrence, even after discontinuing medication, and it was thought that the likelihood of laryngitis was higher than that of other diseases. No underlying disease that could cause laryngeal paralysis was identified.

In this case, the tumor could not be completely ruled out. However, direct visualization, laryngeal ultrasonography, and CT showed no clear masses suggesting polyps or neoplasia. In the case of tumors that cause diffuse thickening, such as lymphoma, or tumors accompanied by inflammation, such as squamous cell carcinoma, it may be difficult to distinguish only by visual inspection; thus, a cytological examination was performed instead of a biopsy. Even if the tumor was not completely excluded by cytological examination, neutrophils with normal respiratory epithelium and degenerative changes were predominant in the cytological examination, and it was thought that the possibility of laryngitis was higher than that of tumors.

The underlying cause of laryngitis in this cat could not be identified. It has been estimated that the likelihood of infection (e.g., bacterial and viral), aspiration, or inhalation of irritants is high in these circumstances. Mycoplasma felis was confirmed in the PCR test for respiratory infectious agents;but it was difficult to determine the cause of severe laryngitis from this result only because it is a commensal bacterium in the respiratory tract of cats. In a previous study of five cats with acute upper respiratory tract obstruction due to inflammatory laryngeal disease, endotracheal lavage and culture were performed, and aerobic bacteria Enterococcus spp., Pasteurella multocida, Enterobacter cloacae, beta-streptococcus, and coagulase-negative Staphylococcus were identified (1). Because these cats also responded to corticosteroids, they were presumed to have secondary bacterial infections due to viral infection. We decided that additional tests could have a high risk of exacerbating the clinical signs by inflicting additional damage or injury to the affected area in this case, in addition to the clear identification of the pathogens. Though, according to previous studies, invasive tests, such as fine needle aspiration or biopsy, are essential for definitive diagnosis and are highly recommended because they do not adversely affect the cat, contrary to the concerns of the clinician (5,8). A punch biopsy to collect tissues with minimal mucosal damage could have also been attempted in this case.

Resolving the underlying disease that causes the obstruction is a fundamental treatment; If swelling due to inflammation is severe and secondary infection is a concern, as in this cat, anti-inflammatory drugs (corticosteroids) and prophylactic antibiotic treatment may be helpful as supportive therapy (1,8). But, in an emergency, securing a breathing passage as quickly as possible is the first priority (6). Aggressive interventions, such as tracheostomy or cricothyroidotomy, that bypass the larynx are required if intubation is not possible. However, tracheostomy tube placement in cats could have a poor prognosis in cases of complications, such as tube occlusion and dislodgement. Minor complications include partial obstruction of the tube, fever, pneumomediastinum, subcutaneous emphysema, edema, Horner’s syndrome, laryngeal paralysis, cough, vomiting after tube suction, and dislodgement of stay sutures (2). In previous studies, 44% of cats that underwent temporary tracheostomy showed a major complication that could be fatal to survival, with a minor complication rate of 74%. For all that, 43% of cats with temporary tracheostomy were discharged without any complications, and there were no recurrences thereafter (2). These results suggest that mortality can be reduced despite possible fatal complications if treated and managed well. Most of these complications are thought to be preventable through thorough monitoring and aftercare. The tube was maintained until the patency of the laryngeal region was completely confirmed, and the humidity in the cage was maintained high by nebulization. Suctioning of the tube was performed every 4-6 h for excessive mucus, and 0.9% normal saline was dripped directly to minimize mucosal damage, excessive mucus secretion, and increased mucus tenacity. In addition, the cat’s hydration status was appropriately maintained through fluid therapy to ensure normal mucociliary transport and consistency of mucous secretions. Successful management without complications was expected until laryngeal inflammation was completely resolved. Indeed, cats with simple inflammation tended to have a better prognosis than those with a laryngeal mass (e.g., tumor and granuloma) with a high rate of major complications (2,4,7). Permanent tracheostomy tube placement is thought to have a longer maintenance period than temporary tracheostomy, and it is possible that continuous damage to the tracheal mucosa may have had an adverse effect on prognosis. Temporary tracheostomy can relieve respiratory distress until the inflammation and swelling of the larynx are resolved in this case and is considered to be an important emergency procedure for cats with respiratory obstruction. Despite the high complication rate, prognosis is expected to be good if appropriate postoperative care is provided.

In conclusion, although rare, inflammatory laryngeal disease can progress to acute upper airway obstruction, which is life-threatening in cats. An accurate diagnostic approach and emergency treatment are needed. We report a case of a cat with acute respiratory distress due to upper respiratory obstruction. Early diagnosis and appropriate treatment resulted in a good prognosis without recurrence.

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2020R1C1C1008675), and by Korea Institute of Planning and Evaluation for Technology in Food, Agriculture and Forestry (IPET) through Companion Animal Life Cycle Industry Technology Development Program, funded by Ministry of Agriculture, Food and Rural Affairs (MAFRA) (322092-04-1-HD030).

The authors have no conflicting interests.