A rare asthma mimic exposed by basic physiology.
In October 2008, a 44-year-old lady was referred for optimization of her asthma therapy prior to commencing in vitro fertilization treatment. She had been diagnosed with asthma in 2006 following a viral infection and was using inhaled beclamethasone (200 μg twice daily) and inhaled salbutamol when required. In the preceding 18 months, she had made two visits to the emergency room with breathlessness, and improved with nebulized salbutamol and a course of oral corticosteroids. She had felt increasingly breathless over the previous 3 months. There was no other past medical history. Written consent was obtained from the patient.

Clinical examination did not reveal any evidence of expiratory wheeze or inspiratory stridor, and chest radiograph was normal. Spirometry revealed a forced …