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Objective: To assess the current spectrum of causes and clinical features associated with hypersensitivity pneumonitis (HP)., Patients and Methods: We studied consecutive patients with HP diagnosed at the Mayo Clinic in Rochester, Minn, from January 1, 1997, through December 31, 2002. Diagnostic criteria for HP included the following: (1) presence of respiratory symptoms, (2) radiologic evidence of diffuse lung disease, (3) known exposure or a positive serologic test result to an inciting antigen, and (4) no other identifiable cause for the lung disease. If there was no identifiable inciting antigen, 1 of the following 2 criteria was required: (1) lung biopsy specimen that demonstrated features of HP or (2) bronchoalveolar lavage lymphocytosis and high-resolution computed tomographic evidence of ground-glass opacities or centrilobular nodules bilaterally., Results: The mean +/- SD age of the 85 study patients was 53 +/- 14 years; 53 patients (62%) were women. Only 2 patients (2%) were current smokers. Chronic (> or = 4 months) respiratory symptoms were present in 66 patients (78%). Histopathologic confirmation was obtained in 64 patients (75%). The cause was identified in 64 patients (75%), and the most common causes were avian antigens (34%) and Mycobacterium avium complex in hot tub water (21%). Farmer's lung disease accounted for 11% of cases, and an additional 9% were related to household mold exposure. The inciting antigen was not identifiable in 25% of patients., Conclusion: Most patients with HP seen at this tertiary care referral center in the Midwest region of the United States had chronic HP, and the most common causes were exposure to birds and exposure to hot tubs.

Hypersensitivity pneumonitis (HP) is a pulmonary disease with symptoms of dyspnea and cough resulting from the inhalation of an antigen to which the subject has been previously sensitized. The incidence of HP is unknown. A population-based study estimated the annual incidence of interstitial lung diseases as 30:100,000 and HP accounted for less than 2% of these cases. The diagnosis of HP can often be made or rejected with confidence, especially in areas of high or low prevalence respectively, using simple diagnostic criteria. Chest X-rays may be normal in active HP; High Resolution Computed Tomography is sensitive but not specific for the diagnosis of HP. The primary use of pulmonary function tests is to determine the physiologic abnormalities and the associated impairment. Despite the pitfalls of false positive and false negatives, antigen-specific IgG antibodies analysis can be useful as supportive evidence for HP. Bronchoalveolar lavage plays an important role in the investigation of patients suspected of having HP. A normal number of lymphocytes rules out all but residual disease. Surgical lung biopsy should be reserved for rare cases with puzzling clinical presentation or for verification the clinical diagnosis when the clinical course or response to therapy is unusual. Being an immune reaction in the lung, the most obvious treatment of HP is avoidance of contact with the offending antigen. Systemic corticosteroids represent the only reliable pharmacologic treatment of HP but do not alter the long-term outcome. The use of inhaled steroids is anecdotal. Treatment of chronic or residual disease is supportive.

The diagnosis of hypersensitivity pneumonitis (HP) is difficult and often relies on histopathology. Our objective was to identify diagnostic criteria and to develop a clinical prediction rule for this disease. Consecutive patients presenting a condition for which HP was considered in the differential diagnosis underwent a program of simple standardized diagnostic procedures. High-resolution computed tomography scan and bronchoalveolar lavage (BAL) defined the presence or absence of HP. Patients underwent surgical lung biopsy when the computed tomography scan, BAL, and other diagnostic procedures failed to yield a diagnosis. A cohort of 400 patients (116 with HP, 284 control subjects) provided data for the rule derivation. Six significant predictors of HP were identified: (1) exposure to a known offending antigen, (2) positive precipitating antibodies to the offending antigen, (3) recurrent episodes of symptoms, (4) inspiratory crackles on physical examination, (5) symptoms occurring 4 to 8 hours after exposure, (6) and weight loss. The area under the receiver operating characteristic curve was 0.93 (95% confidence interval: 0.90-0.95). The rule retained its accuracy when validated in a separate cohort of 261 patients. The diagnosis of HP can often be made or rejected with confidence, especially in areas of high or low prevalence, respectively, without BAL or biopsy.