Diagnostic Criteria for Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP), also called extrinsic allergic alveolitis, is a respiratory syndrome involving the lung parenchyma and specifically the alveoli, terminal bronchioli, and alveolar interstitium, due to a delayed allergic reaction. Such reaction is secondary to a repeated and prolonged inhalation of different types of organic dusts or other substances to which the patient is sensitized and hyper responsive, primarily consisting of organic dusts of animal or vegetable origin, more rarely from chemicals.

Hypersensitivity pneumonitis (HP) is a difuse interstitial lung disease caused by repeated and prolonged exposure and sensitization to numerous inhaled antigens in susceptible individuals.

Criteria for the diagnosis of hypersensitivity pneumonitis (HP)

Acute hypersensitivity pneumonitis (HP)

• Can be diagnosed if the following features are fulfilled
  • Exposure to a potentially offending antigen source
  • Recurrent episodes of symptoms, occurring 4–8h after exposure
  • Elevated titre of specific IgG (precipitating) antibodies to an antigen
  • Inspiratory crackles on physical examination
  • High-resolution CT (HRCT) pattern compatible with acute or subacute HP
• If all these features are not fulfilled, one of the following criteria can function as a substitute
  • Bronchoalveolar lavage lymphocytosis
  • Pathology of lung specimen consistent with acute HP
  • Positive laboratory inhalation challenge test (ICT), positive workplace challenge or improvement after avoidance of the suspected exposure

Chronic HP

• Can be diagnosed if four or more of the following criteria are fulfilled
  • Exposure to a potentially offending antigen source
  • Elevated titre of specific IgG (precipitating) antibodies to an antigen or bronchoalveolar lavage lymphocytosis
  • Reduced diffusing capacity for carbon monoxide and/or hypoxaemia at rest or exercise
  • HRCT pattern compatible with chronic HP
  • Pathology of lung specimen compatible with chronic HP
  • Positive laboratory ICT, positive workplace challenge or improvement after avoidance of the suspected exposure

 

References:

1. Varone F, Iovene B, Sgalla G, Calvello M, Calabrese A, Larici AR, Richeldi L. Fibrotic Hypersensitivity Pneumonitis: Diagnosis and Management. Lung. 2020 Jun;198(3):429-440. [Medline]
2. Riario Sforza GG, Marinou A. Hypersensitivity pneumonitis: a complex lung disease. Clin Mol Allergy. 2017 Mar 7;15:6. [Medline]
3. Costabel U, Miyazaki Y, Pardo A, Koschel D, Bonella F, Spagnolo P, Guzman J, Ryerson CJ, Selman M. Hypersensitivity pneumonitis. Nat Rev Dis Primers. 2020 Aug 6;6(1):65. [Medline]

 

Created Mar 31, 2021.