Definition

The fully developed inflammatory response to antigens in lung parenchyma characterized by exudation of eosinophils and fluid into lung interstitium, conducting airways, and alveolar spaces.

Pathophysiology

• Immunologic basis-supporting evidence generally accepted; mechanisms involved not yet clarified.
• Eosinophilic infiltration and a predominance of CD4+ T cells in bronchoalveolar lavage fluid support the role of a dominant TH2 immune response in the lower airways.
• Evolution of disease-likely determined by characteristics of antigens, host response, and regulation of that response.
• Antigens enter the lower respiratory tract by inhalation or hematogenous routes.
• Chronic exposure to antigens-elicits a humoral and cellular immune response.
• Allergic or hypersensitivity pulmonary disorders-associated with an abnormal humoral antibody response and a cell-mediated immunoregulatory defect.
• Immunoglobulin classes involved-IgE, IgG, and others.
• High numbers of activated macrophages and T-lymphocytes and depressed suppressor T-cell activity-alter cell-mediated immunity.
• Collagenolytic enzyme activity-increased.
• Generally referred to as eosinophilic bronchopneumopathy although at least three disease patterns appear to exist: eosinophilic pneumonitis, eosinophilic bronchitis, and pulmonary eosinophilic granulomatosis.
• Severely affected dogs appear to develop marked granulomatous disease.
• Heartworm disease with pneumonitis-microfilaria may become entrapped in the pulmonary circulation and trigger an immune response.
• Mortality-associated with severe hypoxemia (e.g., low arterial oxygen concentration) and (rarely) severe hemoptysis.

Systems Affected

• Respiratory-lower respiratory tract primarily but nasal cavity can also be involved.
• Cardiovascular-can develop cor pulmonale.

Genetics

N/A

Incidence/Prevalence

N/A

Geographic Distribution

Widespread

Signalment

Signs

Causes

• Purported aeroallergens-spores or hyphae from fungi and actinomycetes; pollen; insect antigens; dust or storage mites, unidentified triggers of the immune response.
• Parasitic antigens-heartworm microfilaria, respiratory parasites.

Risk Factors

• Living in a heartworm-endemic area without receiving preventive medication.
• Dusty or moldy environment.
• Air pollution.

Differential Diagnosis

• Parasitic pneumonia-capillariasis; paragonimiasis; dirofilariasis.
• Fungal pneumonia-histoplasmosis; blastomycosis; coccidioidomycosis; cryptococcosis.
• For eosinophilic pneumonitis-bacterial pneumonia; viral pneumonia (e.g., canine distemper virus and canine adenovirus); rickettsial pneumonia (e.g., ehrlichiosis and Rocky Mountain spotted fever); protozoal pneumonia (e.g., toxoplasmosis); congestive heart failure; bartonellosis.
• For eosinophilic bronchitis-infectious tracheobronchitis; chronic bronchitis.
• For pulmonary eosinophilic granulomatosis-neoplasia (including lymphomatoid granulomatosis); pulmonary abscess; bronchial foreign body.

CBC/Biochemistry/Urinalysis

• Inflammatory leukogram-neutrophilic leukocytosis with or without a left-shift, eosinophilia, basophilia, or monocytosis.
• Absence of eosinophilia does not exclude diagnosis.
• Hyperglobulinemia-suggests chronic antigenic stimulus; rule out occult dirofilariasis.

Other Laboratory Tests

Imaging

• Radiographic findings depend on extent and severity of disease.
• Thoracic radiographs-help document the severity of pulmonary artery disease; reveal interstitial pneumonitis in dogs with dirofilariasis.
• Eosinophilic pneumonitis-linear or miliary interstitial pattern that resembles changes seen with early pulmonary edema or fungal pneumonia; alveolar pattern characterized by increased pulmonary densities with indistinct margins in severely affected patients; tortuous, large pulmonary arteries and right-sided cardiomegaly in patients with dirofilariasis.
• Eosinophilic bronchitis-bronchial pattern with thickened bronchi extending into the periphery of the lung (tram/railroad track and donut signs); bronchiectasis in chronic cases.
• Eosinophilic granuloma-multiple nodular lesions of variable sizes in different lung lobes; patchy, focal alveolar densities; tracheo-bronchial lymphadenopathy possible.

Diagnostic Procedures

• Transtracheal or endotracheal wash appropriate for sample collection.
• Bronchoscopy; yellow-green mucus, polypoid mucosal proliferation, partial airway collapse. Occlusive eosinophilic plaques or granulomas sometimes visible within airways.
• Bronchoalveolar lavage-with or without bronchoscope.
• Bacterial and mycoplasmal culture of bronchoalveolar lavage fluid is recommended to rule-out bacterial infection. Occasionally, concurrent bacterial infection can be identified in dogs with eosinophilic lung disease.
• Fine-needle lung aspiration and examination.
• Cytologic examination of aspirates, washings, or brushings-definitive diagnosis: eosinophilic inflammation predominates; may note other types of inflammatory cells; carefully examine specimens for antigenic sources (e.g., parasites, fungi, or neoplasia).
• Consider intradermal skin or serologic allergen testing-rarely may identify allergens.
• Fecal examinations-routine flotation, direct smear, sediment examination, and Baermann technique to rule out parasitic pneumonia; negative test can occur due to intermittent shedding and empirical therapy warranted in some cases.

Pathologic Findings

• Gross-diffuse, patchy, or nodular firm lesions; usually pale or mottled.
• Histopathologic-eosinophilic, lymphocytic, and macrophagic infiltration of alveolar walls and alveolar spaces; as disease progresses, interstitial infiltrative process becomes fibrotic with obliteration of alveolar spaces, and granulomas can be dispersed within the interstitial fibrosis. Upper respiratory tract epithelium can also be involved with eosinophilic infiltration.

Appropriate Health Care

Inpatient-recommended with multisystemic signs (e.g., anorexia, weight loss, or lethargy).

Nursing Care

• Dehydration-hinders mucociliary clearance and secretion mobilization; maintain normal systemic hydration with a balanced multielectrolyte solution.
• Supplemental oxygen-for respiratory distress.

Activity

Restricted during treatment (inpatient or outpatient).

Diet

Ensure normal intake.

Client Education

Warn client that morbidity and mortality are associated with severe hypoxemia.

Surgical Considerations

Lung lobectomy can be required with large granulomas.

Drug(s) Of Choice

• Corticosteroids-prednisolone or prednisone at 2 mg/kg/day until clinical signs begin to resolve (typically 2–3 weeks); then taper slowly (over months). Maintenance dosages of prednisone are often required long-term (0.125–0.5 mg/kg q48h or every 3 or 4 days for 4–6 months or longer).
• Following adequate control of disease and/or due to side effects of systemic glucocorticoids, inhaled corticosteroids (e.g., fluticasone propionate) can be used in conjunction with a spacing chamber and facemask.
• Antibiotic therapy indicated only if active infection documented on airway culture. Prophylactic therapy could lead to development of antimicrobial resistance.
• Heartworm adulticidal therapy-for heartworm-positive patient; initiate after the patient has been stabilized with corticosteroids and rest.
• Itraconazole or ketoconazole-use antifungal drugs only if the fungal infection is confirmed by cytologic examination or culture.
• Hyposensitization-allergy shots based on results of intradermal skin or serologic testing can be attempted but is not the treatment of choice in most patients. Most dogs will still require steroid therapy.

Contraindications

N/A

Precautions

N/A

Alternative Drug(s)

• Other immunosuppressive drugs (e.g., cyclosporine)-can use when corticosteroids are contraindicated or have been ineffective, although inhaled steroids are preferred. No trial results are available to date.
• Bronchodilators-can be helpful, particularly if wheezes are auscultated or labored respiratory effort is observed; see Bronchitis, Chronic.

Patient Monitoring

• Complete blood count will show resolution of peripheral eosinophilia or neutrophilia.
• Arterial blood gases-most sensitive monitor of progress. Can remain abnormal even with successful management of disease.
• Auscultate patient thoroughly several times daily.
• Thoracic radiographs-improve more slowly than the clinical appearance.

Prevention/Avoidance

• Routine heartworm-prevention medication.
• Consider changing patient's environment if an aeroallergen is suspected.

Possible Complications

Pulmonary embolization-dogs treated with adulticidal therapy for dirofilariasis.

Expected Course and Prognosis

• Prognosis good for mild-to-moderate cases; many patients require long-term treatment with steroids.
• If allergen can be identified and eliminated-suspect improved prognosis.
• Heartworm infection-prognosis depends on severity of pulmonary hypertension, cor pulmonale, and embolization.
• Eosinophilic granulomatosis-prognosis guarded; often disease is progressive.

Associated Conditions

• Dirofilariasis
• Bronchopulmonary fungal infection

Age-Related Factors

N/A

Zoonotic Potential

N/A

Pregnancy/Fertility/Breeding

Corticosteroids and other immunosuppressive drugs are contraindicated in pregnant animals.

Synonyms

• Allergic alveolitis
• Allergic bronchitis
• Bronchitic pulmonary eosinophilia
• Eosinophilic bronchitis or bronchopneumopathy
• Eosinophilic pneumonia/pneumonitis
• Eosinophilic pulmonary granulomatosis
• Extrinsic allergic alveolitis
• Hypersensitivity pneumonitis
• Occult heartworm pneumonia
• Parasitic pulmonary eosinophilia
• Pulmonary infiltrates with eosinophilia (PIE)

See Also

• Cough
• Dyspnea and Respiratory Distress
• Heartworm Disease-Dogs
• Lymphomatoid Granulomatosis
• Panting and Tachypnea
• Respiratory Parasites