[Clinical phenotyping of severe Mycoplasma pneumoniae pneumonia in children]

Objective: To investigate and summarize pediatric patients with severe Mycoplasma pneumoniae pneumonia (MPP) presenting with varied clinical and chest imaging features in order to guide the individualized treatment. Methods: This was a retrospective cohort study. Medical records of clinical, imaging and laboratory data of 505 patients with MPP who were admitted to the Department Ⅱ of Respirology Center, Beijing Children's Hospital, Capital Medical University from January 2016 to October 2023 and met the enrollment criteria were included. They were divided into severe group and non-severe group according to whether lower airway obliterans was developed. The clinical and chest imaging features of the two groups were analyzed. Those severe cases with single lobe ≥2/3 consolidation (lobar consolidation) were further divided into subtype lung-necrosis and subtype non-lung-necrosis based on whether lung necrosis was developed. Comparison on the clinical manifestations, bronchoscopic findings, whole blood C-reactive protein (CRP) and other inflammatory indicators between the two subtypes was performed. Comparisons between two groups were achieved using independent-sample t-test, nonparametric test or chi-square test. Univariate receiver operating characteristic (ROC) curve analyses were performed on the indicators such as CRP of the two subtypes. Results: Of the 505 cases, 254 were male and 251 were female. The age of the onset was (8.2±2.9) years. There were 233 severe cases, among whom 206 were with lobar consolidation and 27 with diffuse bronchiolitis. The other 272 belonged to non-severe cases, with patchy, cloudy infiltrations or single lobe <2/3 uneven consolidation or localized bronchiolitis. Of the 206 cases (88.4%) severe cases with lobar consolidation, 88 harbored subtype lung-necrosis and 118 harbored subtype non-lung-necrosis. All 206 cases (100.0%) presented with persistent high fever, among whom 203 cases (98.5%) presented with inflammatory secretion obstruction and plastic bronchitis under bronchoscopy. Of those 88 cases with subtype lung-necrosis, there were 42 cases (47.7%) with dyspnea and 39 cases (44.3%) with moderate to massive amount of pleural effusion. There were 35 cases (39.8%) diagnosed with lung embolism during the disease course, of which other 34 cases (38.6%) were highly suspected. Extensive airway mucosal necrosis was observed in 46 cases (52.3%), and the level of their whole blood CRP was significantly higher than that of subtype non-lung-necrosis (131.5 (91.0, 180.0) vs. 25.5 (12.0, 43.1) mg/L, U=334.00, P<0.001). They were regarded as subtype "lung consolidation-atelectasis-necrosis". Of those 118 cases with subtype non-lung-necrosis, 27 cases (22.9%) presented with dyspnea and none were with moderate to massive amount of pleural effusion. Sixty-five cases (55.1%) presented with plastic bronchitis and localized airway mucosal necrosis was observed in 32 cases (27.1%). They were deemed as subtype "lung consolidation-atelectasis". ROC curve analyses revealed that whole blood CRP of 67.5 mg/L on the 6-10 th day of disease course exhibited a sensitivity of 0.96, a specificity of 0.89, and an area under the curve of 0.97 for distinguishing between these two subtypes among those with lobar consolidation. Conclusions: Pediatric patients with severe MPP present with lobar consolidation or diffuse bronchiolitis on chest imaging. Those with lobar consolidation harbor 2 subtypes as "lung consolidation-atelectasis-necrosis" and "lung consolidation-atelectasis". Whole blood CRP of 67.5 mg/L can be applied as an early discriminating indicator to discriminate between these two subtypes.