• Extrinsic Allergic Alveolitis (EAA) / Hypersensitivity pneumonitis

    by  • 27/05/2013 • Respiratory

    Extrinsic Allergic Alveolitis (EAA) / Hypersensitivity pneumonitis

    Definition

    1. Widespread diffuse inflammatory reaction in small airways of lung and alveoli in response to ORGANIC dusts.
    2. A restrictive lung disease
    3. P/c: fever, malaise, cough, SOB, tachypnoea, course end-inspiratory crackles, wheeze (due to allergic component of reaction).

     

    Diagnostic/Investigation

    1. Chest xray
      1. o Fluffy nodular shadowing with subsequent development of streaky shadows particularly in upper lobes.
    2. Lung function tests
      1. o Restrictive ventilatory defect (=RLD) with a decrease in carbon monoxide gas transfer (=reduced diffusing capacity of lung).
    3. Polymorphonuclear leukocyte count
      1. o Raised immune cells due to acute inflammatory/hypersensitivity reaction
    4. Precipitating antibodies
      1. o Precipitating Abs in response the Ags present in the serum.
      2. o ¼ of pigeon fanciers have precipitating IgG antibodies against pigeon proteins and droppings in their serum.
    5. Bronchoalveolar lavage
      1. o Increased T lymphocytes and granulocytes (neutrophilia).

     

    Aetiology

    1. Microbial spores contaminating vegetable matter, often acquired by inhalation:

     

    Disease Situation Antigens (mostly fungal)
    Farmers lung Forking mouldy hay or any other mouldy vegetable material Thermophilic actinomycetes eg: Micropolyspora faeni
    Bird fanciers lung Handling pigeons, cleaning lofts or budgerigar cages Proteins present in the bloom on the feathers and in excreta
    Maltworkers lung Turning germinating barley Aspergillus clavatus
    Humidifier fever Contaminated humidifying systems in air conditioners or humidifiers in factories. Possibly a variety of bacteria or amoeba. Eg: Naegleria gruberi
    Mushroom workers Turning mushroom compost Thermoactinomyces
    Cheese washers lung Mouldy cheese Penicillin casei

    Aspergillus clavatus

    Wine makers lung Mould on grapes Botrytis

     

    Pathophysiology

    1. Initial infiltration of the small airways and alveolar walls with neutrophils followed by T lymphocytes and macrophages.
    2. Leading to development of small non-caseating granulomas.
    3. Comprise multinucleated giant cells.
    4. Allergic response to inhaled antigens involves cellular immunity and deposition of immune complexes causing foci of inflammation through the activation of complement (‘classical pathway’).

     

    Treatment/management

    Prevention is aim. 

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