August 29, 2016
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Hypersensitivity Pneumonitis (cont.)

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How is hypersensitivity pneumonitis diagnosed?

Many people with episodes of hypersensitivity pneumonitis are probably unrecognized and undiagnosed. Some cases believed to be viral pneumonias may actually be hypersensitivity pneumonitis. The patient's history of repeated episodes of typical symptoms, hours after exposure to certain environments are important in establishing the diagnosis.

Most patients with this disorder have symptoms of shortness of breath and/or cough. Quite often a chest X-ray may show a variety of abnormalities, but primarily increased lung markings. A specialist in lung disease will primarily depend on a history of exposure either by occupation or hobby. With the abnormal chest X-ray, a high resolution cat scan of the chest is often reviewed. This study shows a detailed image of the appearance of the lung tissue. Lung function tests that examine the lung volumes and the ability for gases to move through the lungs (diffusing capacity) are then performed. Not only are the CT scan and pulmonary function tests useful in diagnosis but they are also useful in following response to therapy.

Blood antibody tests and skin tests against certain offending molds, bacteria, or particles are available, but their results are usually inconclusive. Other more recent tests such as the serum KL-6 (Krebs von den Lungen-6; this test may act as a marker for activity seen in diffuse lung disease) may be used. Infectious causes as well as collagen vascular diseases and cancer must be excluded as a cause of the symptoms and signs, and this may involve a biopsy. Unfortunately the small biopsies obtained with a bronchoscope or a needle are usually inadequate. It is often necessary to perform Video Assisted Thoracoscopic Surgery (a.k.a. VATS), which is an open lung biopsy technique performed by thoracic surgeons under general anesthesia. This procedure allows for a larger sample size and more accurate diagnosis.

The interpretation of these tests is complicated, and is best performed by a doctor experienced in hypersensitivity pneumonitis, often with the help of a pathologist experienced in lung diseases. The most accurate determination of the cause of hypersensitivity pneumonitis is almost always a detailed exposure history. It is not uncommon, however, to be unable to find the causative agent.

Medically Reviewed by a Doctor on 3/14/2016


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