Nonspecific bronchial hyperresponsiveness (NBH) is an entity used to characterize the extreme sensitivity of airways to a variety of stimuli. Patients may respond to chemical, physical, or pharmacological stimuli with shortness of breath, coughing, or wheezing. NBH is not a diagnosis per se, but rather is an airway abnormality that can be measured in the pulmonary function laboratory. Perhaps the best method of quantifying NBH is with the use of methacholine bronchoprovocation testing. The methacholine challenge test (MCT) is performed by having patients inhale the bronchial irritant methacholine, which induces bronchoconstriction in sensitive patients. Subjects without bronchial hyperresponsiveness do not react to methacholine.
A number of diseases are characterized by NBH including asthma, reactive airways dysfunction syndrome (a syndrome caused from a brief massive exposure of an inhaled irritant, usually occurring in the workplace), chronic bronchitis, bronchiolitis, viral upper respiratory infection, foreign body aspiration, near drowning, smoke inhalation, sarcoidosis, chronic cough, and post-acute respiratory distress syndrome.
We have found it helpful to think of NBH as a physiologic abnormality rather than a disease. NBH can be a feature of the diseases listed above and it can be transient as well as a more lasting abnormality. We have found MCT to be exceedingly useful in our practice to help define the cause of wheezing in our patients in whom reversible airflow obstruction has not been documented.