Harrison - Hypersensitivity Pneumonitis and Pulmonary Infiltrates with Eosinophilia Flashcards
What is HP?
Extrinsic allergic alveolitis - An inflammatory disorder of the lung involving alveolar walls and terminal airways that is induced by repeated inhalation of a variety of organic agents in a susceptible host.
In the US, what are the 3 MC types of HP?
- Farmer’s lung.
- Bird fancier’s lung.
- Chemical worker’s lung.
Farmer’s lung - Cause?
Inhalation of proteins, such as thermophilic bacteria and fungal spores that are present in moldy bedding and feed.
The antigens responsible for farmer’s lung are also responsible for?
- Mushroom worker’s disease - moldy composted growth medium.
- Bagassosis - moldy sugar cane.
- Water-related exposure - molds in air conditioners or humidifiers.
Hot tub lung?
Hypersensitivity reaction to Mycobacterium avium complex, which is present in hot tubs or whirlpools and is differentiated from actual infection.
Interestingly, what is the effect of smoking in HP?
Has been associated with DECREASED incidence of HP - HOWEVER, smoking may lead to a more progressive or severe course of HP once the disease is present.
Pathogenesis of HP - What characterizes the very early (acute) reaction?
An increase in PMNs in the alveoli and small airways.
Pathogenesis of HP - What does studies in animal models suggest?
That the disease is a Th1-mediated immune response to antigen, with IFN-gamma, IL-12, and possibly IL-18 contributing to disease expression - Multiple cytokines interact to promote HP.
Is there a genetic predisposition to the development of HP?
Certain polymorphisms of the TNF-alpha promoter region and major histocompatibility complex reportedly confer an enhanced susceptibility to pigeon breeder’s disease.
After inhalation of an antigenic particle, the attraction and accumulation of inflammatory cells in the lung may be due to one or more of the following mechanisms?
- Induction of the adhesion molecules L-selectin and E-selectin.
- Elaboration by dendritic cells of CC chemokine 1 (DC-CK-1/CCL18).
- Increased expression of CXCR3/CXCL10 by CD4+ and CD8+ lymphocytes.
- Incr. levels of Fas protein and FasL in the lung (which would be expected to suppress inflammation by induction of T cell apoptosis) is COUNTERBALANCED by increased expression of the inducible anti-apoptotic gene Bcl-xL –> Lower overall level of pulmonary lymphocyte apoptosis in HP patients.
Clinical presentation of HP?
That of an interstitial pneumonitis - Can be acute, subacute, and chronic.
Acute HP - Clinical presentation?
6-8h after exposure: 1. Cough. 2. Dyspnea. 3. Fever/Chills. 4. Malaise. usually clear within a few days if there is no further exposure to antigen. Resembles influenza.
Subacute HP - Clinical presentation?
Often appears insidiously over a period of weeks marked by cough and dyspnea - May progress to cyanosis and severe dyspnea, requiring hospitalization.
Chronic HP - Clinical presentation?
May be indistinguishable from pulmonary fibrosis in its later stages.
- Cough.
- Weight loss.
- Malaise.
- Gradual increase in dyspnea.
Chronic HP - Physical exam may reveal?
- Clubbing.
2. Inspiratory crackles.
Chronic HP - Imaging shows?
- Interstitial fibrosis.
2. Emphysema.
What is the clinical manifestation of chronic HP with the greatest predictive value for mortality?
Pulmonary fibrosis.
Fibrosis appears more prominent in HP associated with?
Birds.
Emphysema appears more prominent in HP associated with?
Farmer’s lung.
Antigen for bird fancier’s, breeder’s, or handler’s lung?
Parakeet, pigeon, chicken, turkey proteins from avian droppings or feathers.
Antigen for chemical worker’s lung?
Isocyanates from polyurethane foam, varnishes, lacquer.