Pulmonary Infiltration with Eosinophilia

Also known as : PIE - Eosinophillic Lung disease - Eosinophillic Pulmonary Granulomatosis

Introduction

Pulmonary Infiltration with Eosinophilia (PIE) is a broad term describing an inflammatory lung disease in which the predominant infiltrating cell is the eosinophil. It is thought to be an immune mediated condition where the airway abnormalities are a consequence of a hypersensitivity reaction to an unidentified allergen such as microfilariae of heartworms, lungworms, chronic bacterial or fungal infections (eg, histoplasmosis, aspergillosis), viruses, external antigens, and unknown precipitating factors.
Eosinophillic pulmonary granulomatosis is a severe type of PIE seen in dogs and is characterzied by the development of nodules and hilar lymphadenopathy. It is most often associted with a hypersensitivity reaction to microfilarie in heartworm infection.

History & Clincical signs

Eosinophillic lung diseases are seen in young and older dogs. It is rare in the Cat.
Affected dogs usually present because of slowly progressive respiratory signs such as a cough, increased respiratory effort and exercise intolerance, wheezing and occasionally haemoptysis may be seen.The cough may be mild or severe, productive or nonproductive, and progressive or nonprogressive. Systemic signs are rarely present but may include anorexia and weight loss. There may be a history of a recurring cough which is unresponsive to antibiotics but often responsive to corticosteroid therapy. The clinical signs may be seasonal in appearance.
Severely affected animals may exhibit moderate to severe dyspnoea and cyanosis at rest.

Diagnosis

Physical examination

Physical examination is largely normal. Thoracic auscultation may reveal crackles or expiratory wheezes.

Laboratory findings

Eosinophilia may be evident on haematology.

Radiography

The most common radiographic finding is a diffuse Interstitial lung pattern, a bronchial and/or alveolar pattern may also be visible. Eosinophilic Pulmonary Granulomatosis results in the formation of nodules, usually with indistinct borders. Consolidation of lung lobs and a hilar lymphadenopathy may also be seen.

Bronchoscopy

Bronchoscopy may reveal increased amounts of mucous in the airways which may have a greenish appearance. Tracheobronchial washes may show evidence of eosinophillic inflammation. Pulmonary specimens shouldbe carefully examined for the presence of infectious agents and for features of malignancy which may represent potential antigenic sources. Diagnosis may be complicated by the presence of a bacterial secondary infection resultng in a neutrophillic inflammation and a positiove culture on tracheal wash. Once the bacterial infection has been controlled, a second tracheobronchial wash may harvest eosinophils.

Treatment

Any underlying disease needs to be treated directly. Eliminating the source of the antigen that may the triggering the excessive immune response may result in a cure. The most effective management consists of corticosteroids. When PIE is secondary to heartworm disease or pulmonary parasites, treatment with prednisolone before or during treatment antihelmintic treatment controls the pulmonary signs. Prolonged therapy is often needed when the underlying allergen is unknown starting at a high dose and gradually tapering down. When severe bronchoconstriction is suspected, bronchodilators or b2-agonists may be helpful.
Eosinophilic Pulmonary Granulomatosis requires treatment with corticosteroids and a cytotoxic agent such as cyclophasphamide.

Prognosis

The prognosis is fair to good although there is a wide spectrum of disease severity. Some dogs require long term corticosteroid therapy. Eosinophillic Pulmonary Granulomatosis carries a guarded prognosis.

References

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
• Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.