Pneumonitis

Pneumonitis is a general term for inflammation of lung tissue. Chronic inflammation of lung tissue can lead to irreversible scarring (pulmonary fibrosis). Pneumonitis isn't a specific disease but a sign of an underlying problem. Causes of pneumonitis include:

• Pneumonia.
• Inhalation of foreign matter, usually of stomach contents when vomiting (aspiration pneumonitis).
• Exposure to an inhaled allergen (hypersensitivity pneumonitis), e.g. humidifier lung, farmer's lung, bird fancier's lung.
• Adverse reaction to a drug or toxic chemical
• Radiation therapy
• Sepsis: the body's inflammatory response to infection.

• Common if consider all causes of pneumonitis.
• Annual incidence of interstitial lung diseases has been estimated as 30:100,000 with hypersensitivity pneumonitis accounting for less than 2% of these cases.¹

• History of exposure to precipitating cause, e.g. birds, radiotherapy, dusts, drugs, chemicals
• Clinical features will depend on the severity and underlying cause and may include:
  • Shortness of breath
  • Cough
  • Burning sensation in chest
  • Chronic pneumonitis may lead to fatigue, weight loss, exercise intolerance, cyanosis and finger clubbing.

Any other cause of acute, subacute or chronic respiratory distress or cough, e.g.

• Infection, including Legionella, Q fever, tuberculosis
• Sarcoidosis
• Lung cancer.

• Blood tests: full blood count (may be raised neutrophilia, lymphocytosis, eosinophilia), raised ESR and CRP, hypoxaemia.
• Sputum or culture of lung secretions with bronchoscopy.
• Chest X-ray: may be normal or show micronodular or reticular opacities.
• CT scan: may also be normal but far more sensitive. May show diffuse, patchy ground-glass attenuation and small, poorly defined centrilobular nodules; patchy areas of air-trapping; evidence of pulmonary fibrosis and honeycombing may be seen in chronic and advanced disease.
• Pulmonary function tests: spirometry usually shows restrictive changes but may be a mixed obstructive/restrictive picture.
• Lung biopsy: occasionally required if other tests fail to establish the diagnosis.

• Avoidance of any established precipitating cause.
• Treatment of pneumonitis depends on the underlying cause and may include medications such as:
  • Systemic corticosteroid therapy can speed resolution of hypersensitivity pneumonitis.
  • Antibiotics for infection.

• Severe acute or subacute flares may cause severe respiratory distress and can be life threatening
• Recurrent pneumonia
• Pneumothorax
• Pulmonary fibrosis
• Cor pulmonale
• Chronic obstructive pulmonary disease.

• Prognosis is good with early diagnosis and management.
• Late diagnosed chronic pneumonitis may lead to progressive, irreversible lung disease.

Avoid exposure to the cause, e.g. control; of occupational hazards, routine maintenance of heating, ventilation and air-conditioning equipment.