Extrinsic allergic alveolitis Flashcards
What is extrinsic allergic alveolitis?
interstitial inflammatory disease of the distal gas-exchanging parts of the lung caused by inhalation of organic/antigenic dusts.
What is extrinsic allergic alveolitis also known as?
hypersensitivity pneumonitis (HP).
What is the aetiology of extrinsic allergic alveolitis?
In sensitised individuals, repetitive inhalation of allergens provokes a hypersensitivity reaction which varies in intensity + clinical course depending on the antigen.
In the acute phase, the alveoli are infiltrated with acute inflammatory cells.
Antigenic dusts include microbes + animal proteins
Give examples of extrinsic allergic alveolitis
Farmer’s Lung: mouldy hay containing thermophilic actinomycetes
Pigeon Fancier’s Lung: blood on bird feathers + excreta
Maltworker’s Lung: barley or maltlings containing Aspergillus clavatus
Bagassosis or sugar worker’s lung (Thermoactinomyces sacchari)
Describe the epidemiology of extrinsic allergic alveolitis
UNCOMMON
2% of occupational lung disease
50% of reported cases affect farm workers
Geographical variation
List 6 symptoms of acute extrinsic allergic alveolitis
REVERSIBLE episodes of: Dry cough Dyspnoea Malaise Fever Myalgia Wheeze + productive cough may develop if repeat high-level exposure
List 4 symptoms of chronic extrinsic allergic alveolitis
Slowly increasing breathlessness
Decreased exercise tolerance
Weight loss
Exposure is usually chronic, low-level + there may be no hx of previous acute episodes
Give 3 signs of acute extrinsic allergic alveolitis
Rapid shallow breathing
Pyrexia
Inspiratory crackles: Bi-basal rales (crackles at base of lungs, present during acute HP but not between episodes
Give 2 signs of chronic extrinsic allergic alveolitis
Diffuse fine inspiratory crackles (rales)
Clubbing (rare)
What bloods should be taken in extrinsic allergic alveolitis?
FBC: neutrophilia, lymphopenia, high ESR, normocytic normochromic anaemia
ABG: reduced PO2 + PCO2
Albumin may be low: but non-specific
What investigations are performed for extrinsic allergic alveolitis?
Bloods ABG CXR High Resolution CT-Thorax Pulmonary Function Tests Diffusing lung capacity of carbon monoxide
Why perform serology for extrinsic allergic alveolitis?
Test for IgG to fungal or avian antigens
not diagnostic as may find in normal individuals
What may be seen on CXR in extrinsic allergic alveolitis?
Often NORMAL in acute episodes
Acute: fibrosis, upper zone mottling/ consolidation
Hilar lymphadenopathy in rare cases
Chronic: upper zone fibrosis, honeycomb lung
What may be seen on high resolution CT in extrinsic allergic alveolitis?
Detects early changes
Chronic: Patchy ‘ground glass’ shadowing + nodules, extensive fibrosis
Used in chronic HP to confirm dx
What may be seen on pulmonary function tests in extrinsic allergic alveolitis?
ACUTE: restrictive pattern (low FEV1, low FVC)
SUBACUTE/ CHRONIC: obstructive + restrictive pattern