In our large sample study, consolidation was a stable and reliable feature in assessing disease severity and prognosis in patients with MPP. Lobar consolidation was independently associated with a higher risk of SMPP, longer fever duration and length of stay, and higher costs. These results demonstrated that an increased number of lobar consolidations could predict the severity of MPP and significantly enhance the accuracy of clinical outcome prediction in patients with MPP at an early stage.
Radiographic manifestations of MPP vary, including bronchial wall thickening, reticulonodular, segmental and lobar consolidations, atelectasis, hilar lymphadenopathy, and pleural effusion. Of these, consolidation as a CT feature presents a homogeneous increase in lung parenchymal attenuation that obscures the margins of vessels and airway walls . In this study, consolidation was the second most common imaging feature and had good stability in evaluating the MPP course. The incidence of consolidation was up to 86.6% in patients with duration of fever ≤3 days, and 88.5% for duration of fever >9 days. In other words, the rate of consolidation was quite high in the early stages of infection and did not increase significantly with an increase of fever duration before admission, which may be relevant to type Ⅳ hypersensitivity. Furthermore, we found that an increased number of lobar consolidations was associated with higher odds of SMPP. As a previous literature has reported, patients with consolidations were more likely to have hypoxia, tachypnoea, tachycardia, and extrapulmonary manifestations, which indicate severe pneumonia in children, than those without consolidation on CR . However, to our knowledge, no study has investigated the association between the number of lobar consolidations and SMPP. This is the first study to achieve a quantitative evaluation of consolidation, which is superior to the previous vague assessments of large-area and multilobe consolidations.
Inflammatory cytokines were involved in the immunopathogenesis of Mycoplasma pneumoniae infection [14, 19]. In our study, we found a positive correlation between lobar consolidation and LDH, IL-2R, and CRP levels in children with MPP, which is consistent with the findings of previous studies [12,14]. Mycoplasma pneumoniae attach to the ciliated epithelial cells on the respiratory tract through the P1 protein, exerting cytotoxicity by expression of community-acquired respiratory distress syndrome and production of hydrogen peroxide, then activating host immunity, including macrophages, mast cells, neutrophils, and natural killer cells, as well as T and B lymphocytes and humoral immune responses . Cell-mediated immunological responses play an important role in the development of MPP. In SMPP, the immune response is exaggerated, and interleukin levels are elevated, resulting in diffuse alveolar damage with fibrinous exudates within the alveolar lumens histopathologically, which was correlated with consolidation on CT .
The association of multilobar involvement with prognosis has been previously investigated in some studies [12, 22, 23]. Patients with more lobar consolidations experienced longer fever duration, length of stay and higher costs, which are consistent with the results of this study. Some previous studies suggested that prolonged fever duration was associated with MP macrolide resistance [24,25]. We investigated the presence of macrolide-resistant genes through convenience sampling and found that almost MP were shown to have an A-to-G transition mutation at position 2063 in the 23S rRNA genes. Meanwhile, one study revealed that the presence of homogeneous lobar consolidation was responsible for prolonged fever ≥7 days after the initiation of macrolides regardless of macrolide resistance. Hence, quantitative analysis of consolidation can be more accurate in predicting the clinical course of MPP and guide rational clinical medication, with major clinical significance.
Clinicians are cautious about using CT in children because of the problem of radiation dose. First, we used a low-dose CT assessment of MPP in this study. According to scans parameters, when patients weigh < 20 kg, the patient absorbs about 0.4–0.8 millisieverts (mSv) of radiation, equivalent to the dose of 4–8 chest radiographs, and when patients weigh 20 kg to 60 kg, the patient absorbs about 0.7–1.6 mSv, equal to the dose of 7–16 chest radiographs . Therefore, low-dose CT scans ensure safe radiation doses in children. Second, in contrast to the 33–79% incidence of consolidation currently reported [10, 11], our results showed that the proportion of patients with consolidation was up to 90.3%, which is attributed to the superiority of CT over X-ray for demonstrating lesion patterns and lung anatomy . Consolidation of a large area or an entire lobe can be clearly observed on CR and CT, while patchy consolidation indicative of bronchopneumonia on CT may manifest as a non-consolidative feature on CR. Additionally, we performed quantitative evaluation of consolidation. It was evident that the quantification of consolidation by CR was not achievable. Finally, low-dose CT is recommended for assessment when patients fail to respond to treatment, had severe complications suggested by CR, or when there is a need to exclude HIV infection and tuberculosis . CT examination is an important and indispensable method. Thus, using low-dose CT can not only ensure safety but also improve the validity of assessment. Low-dose CT is recommended for children with MPP with poor efficacy or requiring differential diagnoses.
Our study has some limitations. First, this study was conducted retrospectively, and therefore analysis was limited to the patient’s available medical records. Second, we are unable to obtain the patients’ lung pathological specimens, as a result, the correlation analysis between imaging and pathology could not be performed. Considering the repeatability and operability of the study, CT is a non-invasive examination that can best reflect the actual pathological condition. Third, as the present study was performed at a tertiary hospital, patients may present with more severe diseases than are usually admitted in primary or secondary hospitals; however, the presented associations among evaluated variables are still present and convincing.