Hypersensitivity pneumonitis (allergic)

Chest | Allergy & Immunology | Hypersensitivity pneumonitis (allergic) (Disease)


Hypersensitivity pneumonitis (HP) (also called extrinsic allergic alveolitis) is a hypersensitivity syndrome that causes diffuse interstitial lung disease from the inhalation of antigenic organic particles.

Causes and Risk factors

Many types of dust can cause allergic reactions in the lungs. Organic dusts that contain microorganisms or proteins and chemicals, such as isocyanates, may cause hypersensitivity pneumonitis. Farmers lung, which results from repeated inhalation of heat-loving (thermophilic) bacteria in moldy hay, is a well-known example of hypersensitivity pneumonitis. Air conditioner lung is another example. It occurs when contaminated humidifiers or air conditioners (especially large systems in office buildings) circulate antigens that are capable of causing a hypersensitivity reaction.

Diagnosis and Treatment

Once the environmental source of inhaled antigen has been identified, primary therapy is to avoid the inciting agent. Acute forms of disease remit without specific therapy. When complete elimination of the allergen exposure is not possible, protective devices may be used. A patient with disease progression in the setting of ongoing exposure should be strongly advised to avoid the antigen. This may require drastic measures, such as relocation to a new job or home.

Corticosteroid therapy may accelerate the initial recovery in persons with severe disease; however, the long-term prognosis is not favorably affected. Prospective studies have shown significant resolution of symptoms with corticosteroid therapy at 1-2 months, but longer-term follow-up offered no advantage over antigen avoidance or placebo. ...