Pneumonitis

Pneumonitis is a general term for inflammation of lung tissue. Chronic inflammation of lung tissue can lead to irreversible scarring (pulmonary fibrosis). Pneumonitis is not a specific disease but a sign of an underlying problem.

Acute chemical pneumonitis causes swelling of the lung tissue, movement of fluid into the air spaces in the lung and reduced ability to absorb oxygen and remove carbon dioxide. In severe cases, death may result from hypoxia.

Chronic pneumonitis may follow low levels of exposure to the irritant over long periods of time, causing inflammation which may lead to fibrosis, resulting in decreased gas exchange and stiffening of the lung, and ultimately leading to respiratory failure and death.

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; many household and industrial chemicals can cause acute and chronic pneumonitis:
  • Exposure to dangerous levels of chlorine gas may occur at home when using cleaning materials, in industrial accidents or when near to swimming pools.
  • Inhalation of dangerous substances can occur during smelting, welding or other metal work, in the production or use of solvents or pesticides, fires and when handling grain.
• 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.
• Blood gases: 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.