Patient characteristics and laboratory findings. According to the inclusion criteria of this study, 126 patients were enrolled in the retrospective cohort as training set, including 41 common Mycoplasma pneumoniae pneumonia (CMPP) and 85 RMPP and 54 patients were enrolled in the prospective cohort, including 17 CMPP and 37 RMPP as test set respectively. No significant difference was found in gender (P=0.268), and age (P=0.889) (Table 1).
The RMPP and CMPP were admitted for 24h to compare clinical symptoms, biochemistry levels, and routine blood markers. PFD, PMTD, the highest temperature within 24 hours of admission, heart rate, AST, CK-MB, and ALB were significantly different in the RMPP group compared to the CMPP group (P<0.05). Respiratory rate, WBC, CRP, Hb, PLT, D-dimer, ESR, PCT, ALT, Tb, CK, and PCD was not significantly different between these two groups (P>0.05) (Table 1).
Model
|
Training set
|
Test set
|
|
CMPP(n=41)
|
RMPP(n=85)
|
P value
|
CMPP(n=17)
|
RMPP(n=37)
|
P value
|
Sex(male/female)
|
21/20
|
44/41
|
0.268
|
12/5
|
22/15
|
0.078
|
Age(years)
|
4.81±2.79
|
4.88±2.79
|
0.889
|
4.81±2.79
|
4.64±2.51
|
0.210
|
T (℃)
|
37.32±1.07
|
38.03±1.28
|
<0.001
|
37.51±1.30
|
37.85±1.35
|
0.388
|
HR
|
116.59±17.62
|
123.74±18.12
|
0.032
|
117.56±14.36
|
123.32±15.51
|
0.201
|
R
|
25.61±4.94
|
26.78±3.84
|
0.079
|
25.62±3.93
|
27.03±3.94
|
0.243
|
WBC(*109/L)
|
9.51±4.56
|
9.71±3.72
|
0.818
|
10.25±4.26
|
9.37±4.66
|
0.508
|
NEUT(*109/L)
|
9.19±4.93
|
9.18±5.23
|
0.997
|
10.12±3.80
|
9.03±5.01
|
0.392
|
Hb (g/L)
|
128.05±33.63
|
122.11±9.86
|
0.257
|
127.13±7.18
|
121.32±10.97
|
0.028
|
PLT (*109/L)
|
277.64±122.79
|
288.94±129.45
|
0.625
|
287.68±119.95
|
294.73±154.05
|
0.859
|
CRP (mg/L)
|
19.95±18.07
|
24.94±36.02
|
0.289
|
23.00±19.28
|
24.54±30.54
|
0.828
|
LDH (U/L)
|
354.16±161.08
|
403.07±167.87
|
0.108
|
317.37±100.80
|
411.19±152.01
|
0.011
|
ESR (mm/h)
|
31.55±15.24
|
30.73±18.16
|
0.786
|
32.88±12.09
|
29.54±18.96
|
0.447
|
MP-DNA(*104)
|
539.98±1598.42
|
1949.96±10820.71
|
0.232
|
249.61±646.86
|
876.30±21411.18
|
0.112
|
D-dimer (ng/L)
|
651.84±1532.27
|
673.84±828.26
|
0.929
|
532.31±1098.19
|
713.05±912.48
|
0.569
|
PCT (ng/mL)
|
0.19±0.37
|
0.17±0.34
|
0.786
|
0.18±0.19
|
0.13±0.15
|
0.386
|
ALT (U/L)
|
15.66±12.93
|
22.52±28.57
|
0.059
|
15.18±11.32
|
20.65±17.89
|
0.188
|
AST (U/L)
|
29.43±10.57
|
35.25±18.01
|
0.021
|
25.94±8.05
|
34.03±14.37
|
0.012
|
TP (g/L)
|
68.42±4.64
|
67.12±5.40
|
0.154
|
69.93±4.57
|
67.78±4.72
|
0.413
|
ALB (g/L)
|
42.73±3.13
|
40.99±4.37
|
0.010
|
42.02±2.77
|
41.34±3.21
|
0.439
|
CK-MB (U/L)
|
73.71±39.50
|
39.5±47.43
|
0.049
|
75.75±50.98
|
65.05±59.70
|
0.511
|
CK(U/L)
|
86.59±71.30
|
67.59±63.11
|
0.137
|
22.50±8.15
|
40.08±34.73
|
0.006
|
PFD(days)
|
5.07±2.71
|
7.04±4.21
|
<0.001
|
5.31±2.52
|
7.92±4.29
|
0.008
|
PCD(days)
|
9.36±7.08
|
11.10±6.02
|
0.326
|
12.19±9.83
|
13.49±28.77
|
0.808
|
PMTD(days)
|
2.22±2.33
|
4.71±3.76
|
<0.001
|
2.63±3.12
|
4.05±3.39
|
0.146
|
Table 1. Clinical characteristics of patients in the training and test cohort. Values are presented as mean ± SD. T temperature, RMPP refractory Mycoplasma pneumoniae pneumonia, CMPP Common Mycoplasma pneumoniae pneumonia, HR heart rate, R respiratory, WBC white blood cell, NEUT neutrophil, Hb hemoglobin, PLT platelets, CRP C-reactive protein, LDH lactate dehydrogenase, ESR erythrocyte sedimentation rate, PCT procalcitonin, ALT alanine aminotransferase, AST aspartate aminotransferase, TP Total Protein, ALB albumin, CK-MB creatine phosphokinase isoenzyme, CK creatine kinase, PFD preadmission fever duration, PCD
preadmission cough duration, PMTD preadmission macrolides therapy duration.
Chest CT Quantitative Analysis. Quantitative lung features on CT are summarized in Table 2. The RMPP had a higher volume of pulmonary lesions (P<0.001) and higher extent of lesions located in the lung of the right upper lobe(p<0.001) and right lower lobe (P<0.002) compared to the CMPP. The log2Φ of RMPP was higher than CMPP (P<0.001).
|
Training set
|
Test set
|
CMPP(n=41)
|
RMPP(n=85)
|
P value
|
CMPP(n=17)
|
RMPP(n=37)
|
P value
|
Log2Φ
|
15.63±1.31
|
16.78±1.08
|
<0.001
|
15.50±1.26
|
16.66±1.10
|
0.002
|
Total lung volume(cc)
|
827.93±368.40
|
858.92±447.52
|
0.672
|
954.93±419.52
|
799.47±325.31
|
0.199
|
Volume of lung infiltration(cc)
|
71.72±65.43
|
139.68±104.62
|
<0.001
|
66.77±74.78
|
127.96±94.10
|
<0.016
|
Percentages of lung infiltration(%)
|
5.17±5.45
|
8.98±6.50
|
<0.001
|
3.65±5.73
|
8.95±6.46
|
0.006
|
right upper lobe(%)
|
37.13±20.78
|
49.99±21.10
|
<0.001
|
7.57±13.72
|
23.71±25.09
|
<0.004
|
middle lobe of right(%)
|
11.92±24.24
|
18.87±28.69
|
0.101
|
7.79±21.38
|
18.00±29.22
|
0.229
|
right lower lobe(%)
|
11.23±18.17
|
28.30±31.47
|
0.002
|
8.87±17.64
|
32.69±33.37
|
0.001
|
left upper lobe(%)
|
10.51±22.09
|
19.45±29.49
|
0.083
|
6.37±21.71
|
13.50±23.13
|
0.269
|
left lower lobe(%)
|
13.44±23.68
|
22.85±28.39
|
0.046
|
17.46±28.09
|
17.83±28.49
|
0.966
|
Table 2. Quantitative CT parameters of patients in the training and test set. CT Computed tomography, CMPP Common Mycoplasma pneumoniae pneumonia, RMPP refractory Mycoplasma pneumoniae pneumonia.
Logistic regression and nomogram. We used the logistic regression model through stepwise use of Akaike’s information criterion (AIC) to select the variables for the clinical model, the imaging model and the clinical-imaging model. Once the AIC value no longer decreases, the stepwise regression analysis is terminated, and the optimal regression equation was output.
Multivariate logistic regression was used to develop a clinical model, imaging model and clinical-imaging model (Table 3). We enrolled the PFD, PMTD, temperature and AST as predictors for the clinical model, Log2Φ as predictor for the imaging model and the clinical-imaging model enrolled the clinical makers and Log2Φ as predictors in a logistic regression analysis. Variables were presented in the model by using the following formula:
Clinical model:
Probability of RMPP*100= -2272+54.7T+2.6AST+14.9PFD+34.2PMTD
Imaging model:
Probability of RMPP*100= -1315+85.3Log2Φ
Clinical-imaging model:
Probability of RMPP*100= -4709+142.1Log2Φ+1.7AST+8.5PFD+57.1PMTD
|
Variable
|
β
|
OR
|
95%CI for OR
|
Clinical model
|
T
|
0.547
|
1.728
|
1.203, 2.483
|
AST
|
0.026
|
1.026
|
0.987, 1.066
|
PFD
|
0.149
|
1.161
|
0.997, 1.351
|
PMTD
|
0.342
|
1.408
|
1.179, 1.680
|
Imaging-model
|
Log2 Φ
|
0.853
|
2.347
|
1.642, 3.532
|
Clinical-imaging model
|
Log2 Φ
|
1.421
|
4.141
|
2.251, 7.621
|
T
|
0.578
|
1.782
|
1.164, 2.728
|
AST
|
0.017
|
1.018
|
0.972, 1.067
|
PFD
|
0.085
|
1.089
|
0.916, 1.294
|
PMTD
|
0.571
|
1.768
|
1.385, 2.258
|
Table 3. Multiple models with a combination of clinical and imaging parameters by stepwise logistic regression analysis predicting the RMPP. PFD preadmission fever duration, PMTD preadmission macrolides therapy duration, OR odds ratio.
The ROC of the training set was plotted in Fig. 2A with AUROC of 0.810, 0.764 and 0.897, and the test set was plotted in Fig. 2B with area under the receiver operating characteristic curve (AUROC) of 0.782, 0.769 and 0.895 respectively. The AUC (area under curve) value of the Clinical-imaging model (0.897, 95% CI:0.835,0.957) was significantly higher than the Clinical model (0.810, 95% CI:0.734,0.887, P=0.012) and the imaging model (0.764, 95% CI:0.675,0.854, P<0.000). Independent verification conducted in the validation cohort also showed improved performance with clinical-imaging markers being 0.895(95% CI:0.789,1.000).
A nomogram was developed by incorporating the predictors in the clinical-imaging model (Fig.3). The nomogram was created by giving each independent influencing element a weighted score. The highest score is 120 points, and the range of RMPP incidence is 0.1 to 0.9. A higher chance of occurrence is indicated by a larger score obtained by adding the distribution points of each high-risk factor in the nomogram.
Model evaluation. Fig.4A and Fig.4B present graphical representations of calibration of the training set and the test set separately, the solid line represents the performance of the clinical-imaging model, of which a closer fit to the diagonal dotted line represents a better prediction.
We subsequently compared the clinical performance of the integrated model to the clinical model and imaging model separately using decision curve analysis. Fig.5A and Fig.5B illustrate the decision curves for the three models to predict the correct diagnosis of RMPP in the training set and test set. The decision curve analysis graphically shows the clinical usefulness of each model based on a continuum of potential thresholds for diagnosis of RMPP risk (x-axis) and the net benefit of using the model to risk stratify patients (y-axis) relative to assuming CMPP. In this analysis, the clinical-imaging model provided a larger net benefit across the range of diagnosis of RMPP compared with both the clinical model.