Extrinsic allergic alveolitis Flashcards
What is extrinsic allergic alveolitis?
Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is the result of non-IgE mediated immunological inflammation.
HP is caused by repeated inhalation of non-human protein, which can be of natural plant or animal origin or can be the result of a chemical conjugated to a human airway protein, such as albumin.
- The inflammation of HP manifests itself in the alveoli and distal bronchioles.
- The clinical manifestations of HP depend on the concentration and frequency of exposure.
- The clinical syndromes - acute, sub-acute, and chronic HP - present differently.[1][2]
- Some authors are now reporting that there are only two clinical syndromes; however, they vary as to whether they group sub-acute with the acute or the chronic form.[3][4]
- Many cases of HP are caused by occupational exposure
What is the aetiology of extrinsic allergic alveolitis?
most commonly reported agents are:
- bacteria (e.g., thermophilic Actinomycetes, responsible for a variety of syndromes including farmer’s lung, bagassosis, and mushroom picker’s lung)
- animal proteins (e.g., avian proteins responsible for diseases including pigeon breeder’s lung, bird fancier’s lung, and budgerigar fancier’s disease), with exposure to large farm animals also implicated
- Fungi
- reactive chemicals e.g. anhydrides (epoxy resin lung disease), diisocyanates, and agents used in metal working are also known causes of HP syndromes
What is the most common cause of occupational extrinsic allergic alveolitis?
exposure to metal-working fluid
- has become the most common cause of occupational HP
- accounting for about half of all case
Name some risk factors for extrinsic allergic alveolitis?
- smoking
- viral infection
- exposure to avian protein antigen
- exposure to mould antigen
- exposure to bacterial antigen
- exposure to diisocyanate (e.g., epoxy resin)
- exposure to acid anhydride antigen (e.g., paint refinisher)
- exposure to metal-working fluid
- Abx: nitrofurantoin, methotrexate, roxithromycin, and rituximab
- herbal supplements with ayurvedic medicine
Summarise the epidemiology of extrinsic allergic alveolitis?
prevalence of HP is not precisely known.
- It most probably varies with the antigen, the exposure concentration, and as yet unidentified host factors.
- In the past, the prevalence among Wisconsin dairy farmers was reported as being 2% to 8%.
- However, with remedying of the damp conditions leading to farmer’s lung, that prevalence has dropped.
- It has been estimated that HP occurs in 6% to 21% of pigeon breeders
What are the presenting symptoms of extrinsic allergic alveolitis? (acute)
symptoms depend on whether the HP is acute, sub-acute, or chronic
- fever
- chills
- malaise
- non-productive cough
- dyspnoea
beginning 6 to 18 hours after acute, high-level exposure
What are the signs of extrinsic allergic alveolitis? O/E? (Acute)
- bibasilar rales O/A
What are the presenting symptoms of extrinsic allergic alveolitis? (sub-acute)
- malaise
- dyspnoea
- productive cough
over weeks to months
What are the presenting symptoms of extrinsic allergic alveolitis? (chronic)
like idiopathic pulmonary fibrosis (insidious development)
- dyspnoea
- productive cough
- weight loss
(due to low-level exposure)
occurring over a period of many months or even years
What are the signs of extrinsic allergic alveolitis? O/E? (chronic)
- diffuse rales O/A
What are some primary investigations for ?extrinsic allergic alveolitis
-
bloods: FBC, ESR, and albumin
- may be high (indicates inflammatory response)
- acute: ~ elevated ESR and leukocytosis with a left shift
- chronic: low albumin and anaemia (non-specific)
-
CXR
- acute + sub-acute: patchy, nodular infiltrates,
- chronic: fibrosis
-
high-resolution CT - only chronic
- ground-glass attenuation and patchy micronodules of fibrosis predominantly in upper lobes
-
PFTs
- abnormal
- restriction or obstruction or both
- diffusing lung capacity of carbon monoxide (DLCO) is reduced in acute and chronic processes
-
bronchoalveolar lavage
- excludes differentials
- confirms diagnosis - useful in chronic
What are some possible secondary investigations for ?extrinsic allergic alveolitis?
-
lung biopsy
- Occasionally performed in patients with atypical features OR
- where there is an absence of an exposure history
