Hypersensitivity Pneumonitis
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Introduction
Hypersensitivity pneumonitis, also known as extrinsic allergy alveolitis, is an immunologically-indiced lung disease by fine organic dust particles.
The Case of...
a simple case introducing clincial presentation and calling for a differential diagnosis to get students thinking.
Causes and Risk Factors
Numerous causative substances have been identified:
- farmer's lung: moldy hay (Thermophilic actinomyces) : 0.1-1/1000 farmers exposed
- bagassosis
- wood worker's
- compost lung: Aspergillis
- tea grower's lung
- office worker's lung: ventilation/humidifiers/air conditioners, and associated sp
- grain worker's lung
- bird fancier's lung
- lab worker's lung: rat fur or urine proteins
- TDI lung
- drug related: antibiotics
~10% regularly exposed hosts develop EAA
Pathophysiology
granulmoas suggests type IV hypersensitivity.
abnormalities suggests lymphocytic alveolitis: low CD4+/CD8+
Signs and Symptoms
- history
- physical exam
History
Acute form: 4-6 hours after intense exposure: fever, chills, malaise, dyspnea, dry cough, lasting 24 hours.
Subacute: insidious onset cough, sputum, exertional dyspnea, weight loss, fine crackles, PFT restriction and decreased DLCO
Chronic: irreversible disease, progressing to cor pulmonale and respiratory failure.
Physical Exam
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
ABG show hypoxemia.
Diagnostic Imaging
Acute disease: Chest X ray is normal or with bilateral mixed interstitial and airspace opacities.
Chronic disease: Interstitial fibrosis leads to peripheral opacities on chest X ray. PFT shows mixed reactive and obstructive patterns.
Differential Diagnosis
It is often misdiagnosed as infectious pneumonia.
Treatments
Recognize and avoid antigen exposure.
Wear a SCBA if avoidance is impossible.
Low dose systemic steroids can be used to control symtoms
Consequences and Course
Chronic hypersensitivity pneumonitis is a serious condition.
Resources and References
Topic Development
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