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Hypersensitivity pneumonitis (also called extrinsic allergic alveolitis, EAA) is an inflammation of the alveoli within the lung caused by hypersensitivity to inhaled organic dusts. Sufferers are commonly exposed to the dust by their occupation or hobbies.
Additional recommended knowledge
Hypersensitivity Pneumonitis (HP) may also be called many different names, based on the provoking antigen. These include:
Of these types, Farmer's Lung and Bird-Breeder's Lung are the most common. "Studies document 8-540 cases per 100,000 persons per year for farmers and 6000-21,000 cases per 100,000 persons per year for pigeon breeders. High attack rates are documented in sporadic outbreaks. Prevalence varies by region, climate, and farming practices. HP affects 0.4-7% of the farming population. Reported prevalence among bird fanciers is estimated to be 20-20,000 cases per 100,000 persons at risk." 
Hypersensitivity Pneumonitis (HP) is categorized as acute, subacute, and chronic based on the duration of the illness.
In the acute form of HP, symptoms may develop 4-6 hours following heavy exposure to the provoking antigen. Symptoms include fever, chills, malaise, cough, chest tightness, dyspnea, and headache. Symptoms resolve within 12 hours to several days upon cessation of exposure.
On chest radiographs, a diffuse micronodular interstitial pattern (at times with ground-glass density in the lower and middle lung zones) may be observed. Findings are normal in approximately 10% of patients." In high-resolution CT scans, ground-glass opacities or diffusely increased radiodensities are present. Pulmonary function tests show "diffusing capacity of lungs for carbon monoxide. ... Many patients have hypoxemia at rest, and all patients desaturate with exercise.
Patients with subacute HP gradually develop a productive cough, dyspnea, fatigue, anorexia, weight loss, and pleurisy. Symptoms are similar to the acute form of the disease, but are less severe and last longer. On chest radiographs, micronodular or reticular opacities are most prominent in mid-to-upper lung zones. Findings may be present in patients who have experienced repeated acute attacks.
In chronic HP patients often lack a history of acute episodes. They have an insidious onset of cough, progressive dyspnea, fatigue, and weight loss. Removing exposure results in only partial improvement. ... Clubbing is observed in 50% of patients. Tachypnea, respiratory distress, and inspiratory crackles over lower lung fields often are present.
On chest radiographs, progressive fibrotic changes with loss of lung volume particularly affect the upper lobes. Nodular or ground-glass opacities are not present. Features of emphysema are found on significant chest films and CT scans.
Chronic forms reveal additional findings of chronic interstitial inflammation and alveolar destruction (honeycombing) associated with dense fibrosis. Cholesterol clefts or asteroid bodies are present within or outside granulomas.
In addition, many patients have hypoxemia at rest, and all patients desaturate with exercise.
The diagnosis is based upon a history of symptoms after exposure to the allergen and clinical tests. A physician may take blood tests, seeking signs of inflammation, a chest x-ray and lung function tests. The sufferer shows a restrictive loss of lung function.
The best treatment is to avoid the provoking allergen, as chronic exposure can cause permanent damage. Sufferers might try a face mask if they cannot avoid the allergen. Corticosteroids such as Prednisolone may help to control symptoms but may produce side-effects.
Oxford Handbook of Clinical Medicine
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hypersensitivity_pneumonitis". A list of authors is available in Wikipedia.|