What is it?

Extrinsic Allergic Alveolitis (EAA), also known as hypersensitivity pneumonitis, is a group of pulmonary conditions mediated by inflammatory reaction to inhaled allergen that can induce lung fibrosis. Usually, this condition develops after several years of exposure to the inciting agent. The inflammation caused to the lung parenchyma and airways is diffused and granulomatous. There are acute, subacute and chronic forms of the disease. There is maybe a genetic predisposition to this condition and some say that a viral trigger could initiate the flare. known antigens are avian, mammalian protein, fungi, spores, bacterial antigen and small-molecular-weight chemicals. Common occupations are farmers, bird-fancier’s, cheese- workers, malt-workers, chemical workers, and mushroom workers.

20 Alikes with Extrinsic Allergic Alveolitis (EAA)

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Additional names

This group contains additional names:
- Hypersensitivity Pneumonitis (HP)
- Malt Workers' Lung
- Mushroom Workers' Lung
- Farmers' Lung
- Maple Bark-Strippers' Lung
- "Ventilation" Pneumonitis
- Bird-Fanciers' Lung
- Bagassosis
- Suberosis

Signs & symptoms

The acute form symptoms may begin 4-8 hours after exposure and it resolves within days. These symptoms include fever, chest tightness, dry cough, dyspnea, malaise, chills, headache, anorexia and tiredness. The subacute form has a more gradual onset, and its symptoms may include productive cough, dyspnoea, fatigue, anorexia and weight loss. In the chronic form there are typically no systemic symptoms except weight loss and dyspnea. There could be cyanosis and clubbing. After many years, chronic hypoxemia and pulmonary hypertension develop, leading to right heart failure.


Diagnosis of extrinsic allergic alveolitis includes medical history, physical examination, blood tests may search for non-specific inflammatory markers and antigen-specific IgG antibodies. The acute form may appear normal on chest X-ray, or it can show diffuse micronodular interstitial shadowing. The subacute form may show on X-ray micronodular or reticular opacities in the mid or upper lung fields. In the chronic form, X-ray may show fibrosis features with loss of lung volume. CT scan can evaluate the stage of the disease. Inhalation challenge tests can produce symptoms after inhaling the suspected allergan. In bronchoalveolar lavage there is usually lymphocytosis and CD4/CD8 ratio is less than 1. A biopsy can also be performed to look for histopathological features.


Treatment may include avoidance of exposure to the allergan, corticosteroids sometimes may be helpful. As steroid- sparing therapy, azathioprine and mycophenolate mofetil have been used. Oxygen may help as supportive treatment.

☝️ This is not a substitute for professional medical advice. Please consult with your physician before making any medical decision.

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