Assessment for Bronchial Hyperreactivity
On the basis of the degree of bronchial hyperreactivity measured by MIC, our patients fell into two significantly different and distinct groups (Fig 1). Twenty-two patients had normal MICs with a mean decrease in FEV! from baseline of 4 percent; this response was almost identical with that of our control group, who had a mean decrease in FEV! from baseline of 5 percent. On the other hand, 12 patients had abnormal MICs with a mean decrease in FEVj from baseline of 28 percent. Consequently, MIC allowed us to determine that 22 of the 34 patients with a history of wheeze were almost certainly not asthmatic (normal MIC), while 12 had a degree of bronchial hyperreactivity consistent with bronchial asthma (abnormal MIC).
Predictive Value of a History and Physical Examination Using a positive MIC as a standard asthmatic indicator for comparison (Fig 2), the probability that a history of wheeze was predictive of asthma was only 35 percent; the probability that a prior clinical diagnosis of asthma, diagnosed by another physician, was pre-dicitive of asthma, was 62 percent; and the probability that scattered monophonic wheezing, heard by us, was predictive of asthma was only 43 percent.Each patient was seen by a pulmonary specialist who, on the basis of history and physical examination, noted his subjective assessment of the likelihood that each patient had bronchial asthma as the explanation for his symptoms. From our initial clinical diagnostic evaluation prior to the performance of spirometry preinhalation and postinhalation of methacholine, we believed that 13 patients were very likely to have asthma, while seven were very likely not to have it. In 14 patients we were not certain. Compared to the final diagnosis, the accuracy of the pulmonary specialists initial clinical assessment was as follows: only seven of the 13 patients (54 percent) considered very likely to have asthma had asthma as their final diagnosis; none of the seven patients considered unlikely to have asthma had it.
Predictive Value of Routine Spirometry
Results of routine spirometric study appear in Table 1. Although FVCs as percent predicted for patients with normal and abnormal MICs were similar, FEV/ FVC% and FEF25-75%, expressed as a percentage of predicted were not. The mean FEV7FVC of 77 percent for patients with abnormal MIC was significantly less than the mean value of 85 percent with normal MICs, (t= —4.66, p<0.001); the mean FEF25-75%, as a percent of predicted, of 72 percent in patients with abnormal MICs was significantly less than the mean value of 104 percent in patients with normal MICs (t= -4.01, p<0.001). However, although the mean values were significantly different, there was a great deal of overlap (Fig 3). Consequently, because of this overlap, the value of spirometry for predicting the presence of bronchial hyperreactivity in our patients was minimized. It is important to note, however, that since none of our patients had significant baseline obstruction, spirometry postbronchodilator was not performed. It is likely that in the setting where baseline obstruction is present, a significant improvement in spirometric indices in response to the administration of a bronchodilator would be of considerable value in the diagnosis of bronchial asthma.
Spectrum and Frequency of the Causes of Wheeze
Using the final, posttreatment, diagnostic criteria, a specific diagnosis was made in all but one patient. Postnasal drip was the cause of wheeze in 16 (47 percent) of our patients. The cause of postnasal drip was allergic rhinitis in three patients, perennial non-allergic rhinitis in 12, and sinusitis in one. Bronchial asthma was the cause of wheeze in 12 patients (35 percent), a psychogenic illness in four (12 percent) and industrial bronchitis in one (3 percent). One patient had a final diagnosis of familial Mediterranean fever. We were never able to determine the cause of her wheeze. Her initial diagnosis had been postnasal drip from perennial nonallergic rhinitis; however, her symptoms did not resolve with therapy lor postnasal drip. Moreover, further evaluation revealed that she had a history of typical bouts of acute polyserositis which had been responsive to colchicine therapy in the past. Bronchoscopic examination revealed no evidence of upper or lower airway obstruction and a bronchial biopsy was negative for amyloid. Her MIC was negative.
Treatment recommendations of asthma:
Figure 1. Patients with abnormal and normal MIC compared to control group. Drop in FEV, from baseline in abnormal group was significantly different (p<0.001) from controls; drop in FEV, from baseline of normal group was virtually identical to the control group. Triangles = patients with wheezing on physical examination prior to MIC.
Figure 2. Predictive value of clinical evaluation in diagnosing asthma. Wheeze by history and physical examination or a prior diagnosis of asthma did not accurately predict a patients response to MIC.
Figure 3. Patients’ baseline spirometric data. Although mean FEV,/FVC,% and mean FEF25-75%, as percent of predicted, were significantly different between abnormal ( ) and normal (-) MIC groups, individual. values overlap, limiting their predictive value in any given patient. Triangles = patients with wheezing on physical examination prior to MIC.
Table 1—Patients Spirometric Values Baseline Premethacholine
|Patient No.||FVC (% pred)||FEV, (% pred)||FEF25-75% (% pred)||FEV1/FVC%|
|M1C||-MIC||MIC –||-MIC||MIC –||-MIC||MIC||-MIC||MIC –||MIC|