Later development of asthma in patients with a negative methacholine inhalation challenge examined for suspected asthma.

A negative methacholine inhalation challenge (MIC) in a patient with suspected bronchial asthma is generally considered to make this diagnosis unlikely. Nevertheless, the patient may later develop asthma. To estimate the proportion that eventually becomes asthmatic, a 10 year follow-up study was carried out on 334 consecutive MIC-negative patients aged 14-80 years. The development of asthma among these patients was assessed on the basis of entitlement to preferential refund from the cost of antiasthmatic therapy granted for them under national health insurance. During the follow-up 30 patients (9%) were granted the refund. There was no significant difference between men and women in this respect. Patients who developed asthma were somewhat older than those who did not. A family history of allergy, allergic rhinitis, and positive reactions to skin prick tests were significantly more common in patients with future asthma. These patients also had a lower mean forced expiratory volume in 1 sec (FEV1) (% of predicted) and a higher mean increase in PEF after an inhaled sympathomimetic than those remaining free from asthma. In multivariate analyses with a logistic model, 3 risk indicators proved independent predictors of future asthma: age, positive family history of allergy, and FEV1 (% of predicted).