Extrinsic allergic alveoltis

Question 1

Define extrinsic allergic aleveolitis.

Answer 1

AKA hypersensitivity pneumonitis

Result of non-IgE mediated immunological inflammation in alveoli and distal bronchioles, caused by repeated inhalation of non-human protein, e.g. natural plant or animal origin or a chemical conjugated to a human airway protein.

Question 2

How do you classify hypersensitivity pneumonitis/EAA?

Answer 2

Acute (develops over hours following exposure)

Sub-acute (develops over weeks to months following exposure)

Chronic (develops over months to years following exposure).

Question 3

What are the most common causative agents of EAA?

Answer 3

The most commonly reported agents are:

• Bacteria (e.g., thermophilic Actinomycetes in farmer’s lung, bagassosis, and mushroom picker’s lung)
• Animal proteins (e.g., avian proteins in pigeon breeder’s lung, bird fancier’s lung, and budgerigar fancier’s disease), + exposure to large farm animals
• Fungi
• Reactive chemicals such as acid anhydrides (epoxy resin lung disease), diisocyanates, and agents used in metal working are also known causes of HP syndrome
• Ingested drugs

Question 4

Which ingested drugs can cause HP?

Answer 4

nitrofurantoin, methotrexate, roxithromycin, and rituximab

Question 5

Describe the pathophysiology of EAA.

Answer 5

Cellullar infiltrate consists of lymphocytes(CD3 CD8 CD4 Th1) plasma cells and neutrophils. Also presents with non-caseating granulomas and activated foamy macrophages. Broncho/bronchiolocentric inflammation and lymphocytic alveolitis

• Acute HP - fever, tachypnoea, dyspnoea, pulmonary infiltrates, restrictive PFTs, reduced diffusing lung capacity of CO(DLCO) due to lymphocytic alveolitis.
• Sub-acute HP - inflammation is not as intense and there is often a fair amount of fibrosis resulting in insidious development over many weeks of malaise, dyspnoea, cough, mixed PFTs and reduced DLCO.
• Chronic HP - little inflammation, fibrosis characteristic of this type, results in dyspnoea,, weight loss, malaise, mixed PFTs and decreased DLCO.

Question 6

What are the symptoms of extrinsic allergic alveolitis?

Answer 6

• Dyspnoea
• Non-productive/productive cough
• Fever/chills
• Malaise
• Weight loss/anorexia

Question 7

What would you find on examination of a patient with EAA?

Answer 7

Bibasilar or diffuse rales are usually present in people with sub-acute and chronic disease.

Approximately 50% of people with chronic HP have clubbing.

NB: rales are like sound of fire crackles, present on inspiration and expiration .

Question 8

What are the risk factors for EAA?

Answer 8

• Bird keeping and other hobbies
• Regular use of hot tubs
• Smoking
• Viral infection
• Specific occupations –>exposure to avian protein/mould/ bacterial /acid anhydride antigen or to metal-working fluid or diisocyanate (e.g.epoxy resin)
• Oral intake of nitrofurantoin, methotrexate, roxithromycin, rituximab
• Herbal supplements with ayurvedic medicine

Question 9

Exposure to what accounts for about half of cases of HP?

Answer 9

Exposure to metal-working fluid

Question 10

Why does smoking/viral infections predispose to HP?

Answer 10

Increases B7 co-stimulatory molecules on macrophages, thereby increasing the macrophage contribution to the inflammation.

Question 11

List 3 types HP diseases caused by avian protein antigen.

Answer 11

• Pigeon breeder’s lung
• Bird fancier’s lung
• Budgerigar fancier’s lung

Question 12

Which bacterial/mould antigens can lead to HP?

Answer 12

Mould:

• Aspergillus
• Alternaria
• Penicillium
• Trichosporum

Bacterial:

• Thermophilic Actinomycetes
• Bacillus
• Pseudomonas
• Acinetobacter
• Klebsiella

Question 13

Descirbe the epidemiology of EAA.

Answer 13

• 6-21% of pigeon breeders
• Makes up less than 2% of all ILD cases
• Prevalence of farmer’s lung in exposed farmers is about 0.5% and 3%
• Can occasionally present in children

Question 14

What investigations would you do for EAA?

Answer 14

• Serology - for specific IgG
• BAL - lymphocytosis
• CXR
• CT chest - upper/mid zone fibrosis
• PFTs and diffusing lung capacity of CO - restrictive or mixed; decreased DLCO
• FBC, ESR, albumin - check for leukocytosis, normocytic normochromic anaemia, elevated ESR, NO eosinophilia

Question 15

What would you see on CXR/CT chest in EAA?

Answer 15

CXR - patchy, nodular infiltrates; fibrosis in chronic HP, may be normal between episodes. Generally CR is not v sensitive.

CT chest - shows ground-glass shadowing/multiple centrilobular ground glass nodules, mosaic attenuation, relative basal sparing.

Question 16

What is the management of EAA?

Answer 16

Avoid precipitants, smoking cessation, pulmonary rehabilitation, supplemental oxygen (at _<_89%)

Oral corticosteroids - may need to be long term but start with 1mg/kg/day then taper with alternate day therapy for 6 weeks

Question 17

What are the complications and prognosis of EAA?

Answer 17

Patients with non-fibrotic disease and allergen avoidance have good prognosis. Any fibrosis is unlikely to normalise.

• Progressive deterioration
• Hypoxaemia
• Death - due to lung destruction