Hypersensitivity pneumonitis: sensitivity of high-resolution CT in a population-based study

Hypersensitivity pneumonitis refers to a group of pulmonary disorders caused by inhalation of organic or inorganic particulates by sensitized persons. The diagnosis relies on a constellation of findings: exposure to an offending antigen, characteristic signs and symptoms, abnormal chest findings on physical examination, and abnormalities on pulmonary function tests and radiographic evaluation. In population-based studies, the sensitivity of chest radiography for detection of this disease is relatively low. The aim of this study was to determine the sensitivity of high-resolution CT (HRCT) for detection of hypersensitivity pneumonitis diagnosed in a population of swimming-pool employees.

Thirty-one symptomatic employees of a recreation center who were referred because of possible hypersensitivity pneumonitis were examined by using chest radiography, HRCT, and fiberoptic bronchoscopy with bronchoalveolar lavage and transbronchial biopsy. Hypersensitivity pneumonitis was diagnosed in subjects who had two or more work-related signs or symptoms, abnormal results on transbronchial biopsies, and abnormal lymphocytosis as shown by examination of bronchoalveolar lavage fluid. The chest radiographs and HRCT scans were interpreted by consensus by two observers who were unaware of the clinical diagnosis.

Only one of 11 subjects with a diagnosis of hypersensitivity pneumonitis had abnormal findings on a chest radiograph. Five had abnormal HRCT findings. The abnormality in each case consisted of small, poorly defined centrilobular nodules with variable profusion. No subject without the disease had abnormal HRCT findings. Those who had granulomas shown by lung biopsy were more likely to have abnormal HRCT findings than were those who had more subtle histologic abnormalities.

The sensitivity of HRCT for the detection of hypersensitivity pneumonitis in a population-based study is greater than that of chest radiography. The finding of poorly defined centrilobular nodules on HRCT scans should prompt consideration of this disease.