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When should a methacholine challenge be ordered for a patient with suspected asthma?

Cleveland Clinic Journal of Medicine. 2008 January;75(1):37-40
January 1, 2008|Cleveland Clinic Journal of Medicine
Edina Swartz, MD;David Lang, MD
Author and Disclosure Information

Edina Swartz, MD
Department of Pulmonary, Allergy, and Critical Care Medicine, Cleveland Clinic

David Lang, MD
Department of Pulmonary, Allergy, and Critical Care Medicine, Cleveland Clinic

Address: David Lang, MD, Department of Pulmonary, Allergy, and Critical Care Medicine, C22, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195.

Dr. Lang has disclosed that he has received honoraria or consulting fees for teaching, speaking, consulting, or serving on advisory committees or review panels for the AstraZeneca, Critical Therapeutics, Dey, Genentech GlaxoSmithKline, Merck, Novartis, Schering/Key, Teva, and Veruscorporations.

POTENTIAL COMPLICATIONS

Methacholine elicits airway narrowing in susceptible people and can cause severe bronchoconstriction, hyperinflation, or severe coughing. However, this procedure is generally well tolerated, and respiratory symptoms inpatients who react to methacholine typically reverse promptly in response to bronchodilators.

Nevertheless, the test should be performed in a pulmonary function laboratory or doctor’s office with available personnel trained to treat acute bronchospasm and to use resuscitation equipment if needed. Informed consent should be obtained and recorded in the medical record after a detailed explanation of the risks and benefits of this procedure and alternatives to it.

CONTRAINDICATIONS

Table 1 summarizes the absolute and relative contraindications to this test.6

Baseline obstruction. A ratio of FEV1 to forced vital capacity less than 70% on baseline spirometry defines airway obstruction, and methacholine challenge for diagnostic purposes would not be indicated.

Furthermore, patients with low baseline lung function, who may not be able to compensate for a further decline in lung function due to methacholine-induced bronchospasm, are at increased risk of a serious respiratory reaction. For this reason, an FEV1 less than 50% of predicted or less than 1.0 L is an absolute contraindication to methacholine challenge testing, and an FEV1 less than 60% of predicted or less than 1.5 L must be evaluated on an individual basis.9

Myocardial infarction or stroke within the previous 3 months, uncontrolled hypertension, and aortic or cerebral aneurysm are absolute contraindications to this procedure, since induced bronchospasm may cause ventilation-perfusion mismatching resulting in arterial hypoxemia and compensatory changes in blood pressure, cardiac output, and heart rate. There is no increased risk of cardiac arrhythmia during methacholine challenge.10

Pregnancy is a relative contraindication to methacholine challenge testing; metha- choline is classified in pregnancy category C.

Inability to perform spirometry correctly is also a relative contraindication, and therefore this test is not recommended for preschool-age children.

SOME DRUGS SHOULD BE HELD

For this test to yield accurate results, the patient should not take any medications that would mask the response. The most common reason for canceling the test is lack of adequate patient preparation. Generally, the recommended periods for withholding medication sare based on their duration of action (Table 2).6,11–15

Other factors that can confound the results include smoking,16 respiratory infection, exercise, and consumption of caffeine (coffee, tea, chocolate, or cola drinks) on the day of the test. Airway responsiveness may worsen due to exposure to allergen or upper airway viral infections. Vigorous exercise could induce bronchoconstriction; therefore, performing other bronchial challenge procedures or exercise testing immediately before methacholine challenge may affect the results.17,18

Bronchial hyperresponsiveness is seen in a variety of disorders other than asthma, such as smoking-induced chronic airflow limitation, congestive heart failure, sarcoidosis, cysticfibrosis, and bronchiectasis, as well as in siblings of asthmatics and in people with allergic rhinitis.19 In these situations, the methacholine test can be falsely positive, and one should interpret the results in the context of the clinical history.

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