WHAT THIS STUDY ADDS:

• Six clinical criteria can identify patients with a high probability of having hypersensitivity pneumonitis.

LAVAL, QUEBEC—Hypersensitivity pneumonitis (HP), a type of interstitial lung disease which includes farmer’s lung and bird fancier’s disease, is rare, difficult to diagnose, and often mistaken for other conditions. Recently, scientists have developed a set of six criteria that can diagnose and differentiate HP from other illnesses with a specificity and sensitivity of 86%.[1]

Yves Lacasse, MD, MSc, and colleagues have identified the following significant predictors of HP:
• Exposure to a known offending antigen.
• Positive precipitating antibodies to the antigen.
• Recurrent symptoms.
• Inspiratory crackles during the physical examination.
• Symptoms occurring four to eight hours after exposure.
• Weight loss.

Dr. Lacasse, who is from the Centre de Pneumologie at the Hôpital Laval in Quebec, said that an important advantage of these criteria is that they can identify patients who have HP without the need for CT or lung biopsy. Another advantage is that these criteria should help establish uniformity in the definition of HP in clinical research.

USING THE CRITERIA

Dr. Lacasse and colleagues used data from 400 patients (116 with HP, 284 without) to develop the prediction criteria, and data from another set of 261 patients (83 with HP, 178 without) to validate them. To confirm the diagnosis, bronchoalveolar lavage, high-resolution CT, or lung biopsies were performed. As expected, the largest predictor of HP was exposure to a known offending antigen, with an odds ratio of 38.8 (CI, 11.6 to 129.6).

To maximize the diagnostic usefulness of the criteria, Dr. Lacasse suggested that “any patient presenting with an interstitial disease or symptoms suggestive of HP should be screened.” He explained, however, that “the key point for proper utilization of the rule is the patient’s history.” He pointed out that HP is unlikely if there is no exposure to any antigen. Therefore, asking about occupational and environmental exposures is important. For example, a farmer or bird owner presenting with pulmonary symptoms would warrant a higher index of suspicion than a patient presenting with similar symptoms but without exposure to an antigen.

Use of the criteria may eliminate the need for more invasive forms of diagnostic testing, such as lung biopsy, although this depends on the patient. “A patient presenting with the full clinical picture of HP (six criteria out of six) has a 98% chance of having HP. In such circumstances, there is no need [for] CT or biopsy,” asserted Dr. Lacasse. Similarly, if the patient presents with only a few of the symptoms, the probability of HP is weak and the examination can be oriented elsewhere. Dr. Lacasse acknowledged, however, that “no prediction rule is perfect.” He added, “If the clinician is not comfortable with the result obtained with the rule …, further investigations may be conducted.”

—Tamara Gibb

Reference
1. Lacasse Y, Selman M, Costabel U, et al. Clinical diagnosis of hypersensitivity pneumonitis. Am J Respir Crit Care Med. 2003;168:952-958.

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