Laryngitis

Laryngitis is an inflammatory condition of the laryngeal mucosa and submucosa, often extending to the vocal folds and epiglottis. It can be acute or chronic, and may be primary or secondary to systemic disease. The larynx serves as a protective sphincter for the lower airways, and inflammation can lead to airway obstruction, voice changes, and respiratory distress. In veterinary medicine, laryngitis is commonly seen in dogs and cats, and can be caused by infectious agents, trauma, irritants, or neoplasia. The condition ranges from mild, self-limiting inflammation to severe, life-threatening obstruction requiring emergency intervention.

The etiology of laryngitis is diverse. Infectious causes include viral agents such as canine distemper virus, canine adenovirus type 2, parainfluenza virus, and feline herpesvirus-1 and calicivirus. Bacterial infections are often secondary, with Bordetella bronchiseptica, Streptococcus spp., and Mycoplasma spp. being common. Fungal infections (e.g., Aspergillus spp., Cryptococcus neoformans) are rare but possible, especially in immunocompromised patients. Parasitic causes are uncommon but can include Oslerus osleri in dogs. Non-infectious causes include trauma (e.g., endotracheal intubation, foreign bodies, bite wounds), inhalation of irritants (smoke, chemicals, dust), and gastroesophageal reflux. Allergic reactions and immune-mediated disorders may also trigger inflammation. Neoplastic conditions such as squamous cell carcinoma, lymphoma, and adenocarcinoma can cause secondary laryngitis. Additionally, chronic coughing or excessive vocalization can lead to mechanical irritation.

Laryngitis occurs in both dogs and cats, with no strong breed or sex predilection. However, brachycephalic breeds (e.g., Bulldogs, Pugs) are predisposed to upper respiratory issues, including laryngitis, due to anatomical abnormalities. Young animals are more susceptible to infectious causes, especially in kennels or shelters. Chronic laryngitis is more common in older animals, often associated with neoplasia or degenerative conditions. Seasonal patterns may reflect viral outbreaks (e.g., kennel cough in autumn/winter). The incidence is higher in multi-pet households and environments with poor ventilation or high stress.

The pathophysiology of laryngitis involves an initial insult (infectious, traumatic, or irritant) that triggers an inflammatory cascade. Mucosal damage leads to release of pro-inflammatory cytokines (e.g., IL-1, TNF-alpha), causing vasodilation, increased vascular permeability, and recruitment of neutrophils and macrophages. This results in edema, erythema, and exudate formation. In viral infections, the virus replicates in epithelial cells, causing cell lysis and desquamation. Bacterial superinfection can exacerbate inflammation. Chronic inflammation leads to mucosal hyperplasia, fibrosis, and potentially metaplasia. Edema of the laryngeal mucosa can narrow the airway lumen, leading to inspiratory stridor and respiratory distress. In severe cases, laryngospasm may occur, causing acute airway obstruction. Systemic effects may include fever, malaise, and secondary pneumonia if the infection spreads.

Predisposing factors include age (young for infectious, old for neoplastic), breed (brachycephalic), environmental factors (exposure to smoke, dust, chemicals), immunosuppression (due to stress, concurrent disease, or drug therapy), and anatomical abnormalities (e.g., elongated soft palate, everted laryngeal saccules). Endotracheal intubation during anesthesia is a common iatrogenic cause. Gastroesophageal reflux can cause chronic irritation. Poor ventilation and overcrowding in kennels increase the risk of infectious laryngitis. Additionally, chronic coughing from any cause can predispose to laryngeal inflammation.

Clinical signs vary with severity. Acute laryngitis may present with a dry, harsh cough, voice change (hoarseness or loss of bark), and mild fever. There may be pain on palpation of the larynx. In more severe cases, inspiratory stridor, dyspnea, and cyanosis may occur due to airway obstruction. Chronic laryngitis often presents with a persistent cough, gagging, and exercise intolerance. Anorexia and lethargy may be seen. In cats, laryngitis can be associated with sneezing, ocular discharge, and oral ulceration if viral (e.g., calicivirus). Physical examination may reveal pharyngeal erythema, laryngeal pain, and palpable thickening. Auscultation may reveal referred upper airway sounds.

Differential diagnoses include: 1) Laryngeal paralysis (common in older Labrador Retrievers; presents with inspiratory stridor and voice change, but no inflammatory signs; diagnosis via laryngeal examination under light sedation). 2) Laryngeal neoplasia (e.g., squamous cell carcinoma, lymphoma; often in older animals, progressive signs, visible mass on laryngoscopy). 3) Tracheal collapse (mainly in small breed dogs; chronic cough, goose-honk cough, cervical tracheal palpation may elicit cough; radiography/fluoroscopy shows tracheal narrowing). 4) Foreign body in the larynx or pharynx (acute onset, gagging, pawing at mouth; imaging or endoscopy reveals foreign material). 5) Brachycephalic airway syndrome (anatomical abnormalities, stertor, exercise intolerance; laryngeal examination may show elongated soft palate, everted saccules). 6) Allergic rhinitis or pharyngitis (seasonal, nasal discharge, sneezing; response to antihistamines). 7) Gastroesophageal reflux (history of vomiting or regurgitation, esophagitis; response to antacids). 8) Fungal rhinitis or laryngitis (e.g., Aspergillus; chronic nasal discharge, destructive lesions on imaging; serology or PCR). 9) Autoimmune diseases (e.g., pemphigus, lupus; skin lesions, positive ANA). 10) Hypocalcemia (can cause laryngospasm; check serum calcium).

Diagnostic workup begins with a thorough history and physical examination, including careful palpation of the larynx and assessment of respiratory effort. If the patient is stable, a complete blood count (CBC), serum biochemistry, and urinalysis are recommended. Thoracic radiographs are indicated to rule out lower airway disease. Laryngeal examination under light sedation or anesthesia is the gold standard; this may include direct visualization of the larynx, assessment of vocal fold movement, and collection of samples (swabs for cytology/culture, biopsy). Advanced imaging (CT or MRI) may be needed for suspected neoplasia or trauma. Endoscopy (bronchoscopy) can evaluate the trachea and bronchi. PCR testing for viral pathogens (e.g., distemper, herpesvirus) may be performed on swabs. In chronic cases, biopsy is essential for histopathology.

CBC may show leukocytosis with a left shift in bacterial infections, or lymphopenia in viral infections. Serum biochemistry is often unremarkable but may reveal elevated globulins in chronic inflammation or neoplasia. In cases of hypocalcemia, serum calcium will be low. Blood gas analysis may show hypoxemia and hypercapnia in severe respiratory distress. Urinalysis is usually normal. Specific biomarkers such as C-reactive protein (CRP) may be elevated. Serology or PCR for infectious agents (e.g., feline herpesvirus, calicivirus, canine distemper) can be performed. In neoplastic cases, cytology or histopathology is diagnostic.

Radiography of the cervical region may show soft tissue swelling of the laryngeal area, but is often unremarkable. Thoracic radiographs are important to rule out aspiration pneumonia or metastatic disease. Ultrasonography can be used to assess laryngeal masses but is limited by air. Computed tomography (CT) provides detailed anatomy and is excellent for evaluating masses, trauma, or abscesses. Magnetic resonance imaging (MRI) offers superior soft tissue contrast and is useful for evaluating neoplasia or inflammation. Endoscopy (laryngoscopy) is the primary imaging modality for direct visualization and biopsy. Fluoroscopy can assess dynamic collapse of the larynx during respiration.

Cytology from laryngeal swabs or fine-needle aspirates may reveal inflammatory cells (neutrophils, macrophages, lymphocytes) and possibly infectious agents (bacteria, fungi). Histopathology of biopsy samples is definitive. Acute laryngitis shows mucosal edema, congestion, and neutrophilic infiltration. Chronic laryngitis may show lymphocytic-plasmacytic infiltration, fibrosis, and epithelial hyperplasia. Neoplastic lesions show characteristic cell types (e.g., squamous cell carcinoma, lymphoma). Special stains (e.g., Gram stain, GMS for fungi) can identify organisms.

Treatment depends on the underlying cause and severity. For mild cases, rest, humidification, and avoiding irritants may suffice. Antibiotics are indicated for bacterial infections (e.g., amoxicillin-clavulanate 12.5-25 mg/kg PO q8-12h, or doxycycline 5-10 mg/kg PO q12h). Anti-inflammatory doses of corticosteroids (e.g., prednisone 0.5-1 mg/kg PO q12h, tapering) can reduce edema. For severe respiratory distress, oxygen supplementation and emergency tracheostomy may be necessary. In cases of laryngeal paralysis, surgical intervention (e.g., arytenoid lateralization) may be required. For neoplasia, surgical excision, radiation, or chemotherapy may be considered. Supportive care includes fluid therapy, nutritional support, and cough suppressants (e.g., hydrocodone 0.22 mg/kg PO q6-8h) if coughing is non-productive. In cases of gastroesophageal reflux, antacids (e.g., omeprazole 0.5-1 mg/kg PO q12h) and prokinetics (e.g., metoclopramide 0.2-0.4 mg/kg PO q8h) are used.

Prognosis is generally good for acute, uncomplicated laryngitis, with resolution within 1-2 weeks. Chronic laryngitis may have a guarded prognosis depending on the underlying cause. Neoplastic laryngitis carries a poor prognosis, especially if malignant. Severe airway obstruction can be life-threatening if not treated promptly. Negative prognostic indicators include progressive dyspnea, cyanosis, and lack of response to therapy.

Recheck examination should be performed 7-14 days after initial treatment to assess response. If clinical signs persist, further diagnostics (e.g., laryngoscopy, biopsy) are warranted. For chronic cases, regular monitoring every 3-6 months may be needed. Serial CBC and biochemistry can monitor for side effects of medications. Repeat imaging (CT or MRI) may be indicated for neoplastic cases. Owners should be advised to monitor for respiratory distress and seek immediate care if it occurs.

Pearls: 1) Always assess the larynx in any patient with inspiratory stridor or voice change. 2) Use light sedation for laryngeal examination to avoid laryngospasm. 3) In brachycephalic breeds, consider concurrent airway abnormalities. 4) In cats, suspect viral causes if oral ulceration is present. Pitfalls: 1) Do not use corticosteroids in cases of suspected bacterial or fungal infection without appropriate antimicrobial coverage. 2) Avoid over-sedation in patients with respiratory distress. 3) Do not overlook the possibility of foreign body, especially in acute onset. 4) Failure to perform biopsy in chronic cases may delay diagnosis of neoplasia.

Antibiotics: Amoxicillin-clavulanate (12.5-25 mg/kg PO q8-12h) for 7-14 days; Doxycycline (5-10 mg/kg PO q12h) for 14-21 days for Mycoplasma or Bordetella. Anti-inflammatories: Prednisone (0.5-1 mg/kg PO q12h) tapering over 7-14 days; Meloxicam (0.1 mg/kg PO q24h) for pain/inflammation. Cough suppressants: Hydrocodone (0.22 mg/kg PO q6-8h) or Butorphanol (0.05-0.1 mg/kg PO q6-12h) for non-productive cough. Antacids: Omeprazole (0.5-1 mg/kg PO q12h) for reflux. Prokinetics: Metoclopramide (0.2-0.4 mg/kg PO q8h) or Cisapride (0.5 mg/kg PO q8h) for reflux. In emergency, oxygen supplementation and possibly tracheostomy. For fungal infections: Itraconazole (5-10 mg/kg PO q12-24h) or Fluconazole (5-10 mg/kg PO q12h). For neoplasia: Chemotherapy protocols vary (e.g., doxorubicin for lymphoma). Always adjust dosages for renal/hepatic impairment and monitor for drug interactions.

Literature supports the use of empirical antibiotics for bacterial laryngitis, but culture and sensitivity are recommended for chronic cases. Studies on canine infectious respiratory disease complex (CIRDC) highlight the role of Bordetella and viruses. Consensus guidelines from ACVIM and ISCAID recommend doxycycline as first-line for suspected Mycoplasma/Bordetella. Corticosteroids are controversial; they may be beneficial for severe edema but should be used cautiously. A study by Johnson et al. (2013) showed that laryngeal paralysis is a common cause of stridor in older dogs, and surgical treatment improves quality of life. For feline calicivirus, supportive care and antivirals (e.g., famciclovir) have been studied. Overall, evidence is limited for specific treatments of laryngitis, and management is often based on clinical experience and extrapolation from other respiratory diseases.