Conflicting Methacholine Challenge Tests

An 11-year-old boy experienced almost daily wheezing, dyspnea on exertion, and sleep perturbation because of cough. In addition, nadir peak expiratory flow (PEF) was below 100 L/min, which was 30% of predicted (328 L/min),1 compatible with severe persistent asthma.2 After the initiation of therapy with 180 g of albuterol 3 times per day, the patient’s domiciliary PEF rose to 200 L/min and his symptoms improved. The patient was subsequently prescribed fluticasone 220 g twice daily. After weeks of combined albuterol and fluticasone therapy, the patient’s PEF was 300 L/min and his symptoms had regressed to a mild intermittent status.2 Three weeks after the initiation of fluticasone therapy the patient presented to the hospital for a methacholine challenge test (test 1). The patient did not take his albuterol or fluticasone on the day of testing. The baseline spirometry was normal (Table 1). Methacholine challenge testing was performed with a modified 5-breath dosimeter technique, nebulizing Provocholine (Methapharm, Brantford, Ontario, Canada) with a DeVilbiss 646 nebulizer (DeVilbiss, Health Care, Somerset, Pennsylvania). The methacholine challenge test revealed a PC20 (the provocational concentration of methacholine that resulted in a 20% decrease in forced expiratory volume in the first second [FEV1]) of 20 mg/mL (Table 2). In response to this “negative” methacholine challenge, the patient was declared “nonasthmatic” by his pediatrician, and the albuterol and fluticasone therapy was discontinued. Shortly after the discontinuance of therapy, the patient’s symptoms and variable PEF returned. Two weeks following the discontinuance of therapy, the patient returned for a repeat methacholine challenge test (test 2). The baseline spirometry was again normal (Table 3); however, this time the patient demonstrated substantial bronchoconstriction in response to methacholine inhalation, with a PC20 of 8.85 mg/mL (Table 4). A PC20 of 4 –16 mg/mL is classified as borderline bronchial hyperresponsiveness;3 however, given the change in PC20 and the accompanying changes in symptoms and PEF variability, methacholine challenge test 2 was interpreted as a positive test for asthma. Jeffrey M Haynes RRT RPFT is affiliated with the Department of Respiratory Therapy, St Joseph Hospital, Nashua, New Hampshire.

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