Clinical Presentation

The acute presentation of HP occurs after a single large exposure to antigen. Acute symptoms commence typically after 4 to 6 hours of exposure and consist of fever, chills, malaise, chest tightness, cough, and dyspnea. Physical exam findings are nonspecific but may include inspiratory crackles on auscultation. Hypoxia may be found. It is important to note that if the individual is removed from exposure, symptoms often resolve within several days. Chest x-ray findings may demonstrate diffuse, ill-defined nodular opacities that can be normal. After severe acute exposures, bilateral infiltrates are seen on chest x-rays. A high-resolution computed tomography (CT) scan of the chest may demonstrate ground-glass changes, typically in the lower lobes; this is a good test to obtain for patients suspected of having HP. Other findings on CT are nonspecific and range from patchy airspace consolidation to rounded small opacities, centrilobular nodules, air trapping, fibrosis, and emphysema (37,75,76).

Hypersensitivity pneumonitis can also present with subacute symptoms or as a chronic process with periodic bouts of acute episodes. Subacute HP has a more gradual onset than the acute form, and weight loss appears to be a prominent feature of this form of HP. Pulmonary function tests will show restriction with decreased carbon monoxide diffusing capacity of the lungs (DLCO), chest x-ray findings may show infiltrates or be normal, and CT

scans may be helpful. Lymphocytosis can be seen with bronchoalveolar lavage (37).

Hypersensitivity pneumonitis can develop into a chronic form in a small percentage of cases. The disease may progress even though exposure to the causative agent has ended. When the exposure is prolonged and chronic, individuals may report malaise, fatigue, and cough that present gradually over days or even weeks. A chest x-ray may show reticular markings in chronic diseases. Repeated exposures to low levels of antigens in organic dusts can lead to insidious pulmonary function loss. Noncaseating granulomas with foreign-body giant cells are typically found on a lung biopsy in subacute and chronic cases. Emphysema can be an important sequela (77,78).

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