Review Question - QID 106808

The methacholine challenge is used to rule out asthma in patients with a relatively low suspicion of asthma.

The methacholine challenge test, also referred to as the bronchial challenge test, is a test in which the patient inhales nebulized methacholine or histamine which causes bronchoconstriction. Histamine acts via the H1 receptor and methacholine utilizes the M3 receptor for bronchoconstriction. The degree of narrowing can then be quantified by spirometry. Asthmatics will react to lower doses of drug, thus allowing a successful diagnosis. Methacholine challenge is a sensitive but not specific test, so is used to rule out asthma when pre-test probability for presence of disease is low.

Pollart et al. review the management of acute asthma exacerbations. They state that in the ambulatory and emergency department settings, the goals of treatment are correction of severe hypoxemia, rapid reversal of airflow obstruction, and reduction of the risk of relapse. Multiple doses of inhaled anticholinergic medication combined with beta2 agonists improve lung function and decrease hospitalization in school-age children with severe asthma exacerbations.

Courtney et al. review the treatment guidelines for childhood asthma, especially focusing on prevention and chronic management. They state chronic care focuses on controlling asthma by treating the underlying airway inflammation. Inhaled corticosteroids are the agent of choice in preventive care, but leukotriene inhibitors and nedocromil also can be used as prophylactic therapy. Long-acting beta2 agonists may be added to one of the anti-inflammatory medications to improve control of asthma symptoms.

Incorrect Answers:
Answer 1: Pulmonary function tests are a set of tests including spirometry, lung volume measurement, and diffusion capacity. While this could be used to diagnose asthma, it is not the first line test to rule out asthma in patients with low likelihood.
Answer 3: A CT scan is not used to diagnosis asthma. Rather, it is more commonly used to identify and characterize structural abnormalities in the lungs.
Answer 4: A chest radiograph would be the first line diagnostic modality in assessing for pneumonia or traumatic complications. However, it is not the first line diagnostic modality for asthma.
Answer 5: Patients with asthma will often have coexisting allergies and will require allergy testing. However, allergy testing alone will not confirm or rule out asthma.