Pneumonia caused by M. pneumoniae mainly in adolescents, the elderly, immunocompetent individuals, and older children. The clinical manifestations include an irritating cough . In recent years, the proportion of refractory M. pneumoniae pneumonia cases have been on a gradual rise. An 11-year-old girl presented fever and cough and was diagnosed with pneumonia upon imaging. She was positive for IgM and RNA of M. pneumoniae. Thus, the diagnosis of M. pneumoniae pneumonia was confirmed.
Obvious hoarseness in this patient caught our attention and we decided to perform bronchoscopy and mNGS of the BALF for further confirmation. By bronchoscopy, obvious pseudomembranes were observed in the trachea. The pathological results were in line with our expectations, that is, the presence of necrotizing bronchitis. The mNGS of BALF suggested the presence of M. pneumoniae Infection only and no other pathogens were detected. The diagnosis of M. pneumoniae-related acute pseudomembranous necrotizing laryngotracheobronchitis was confirmed. To our knowledge, only two other cases of M. pneumoniae-causing pseudomembranous necrotizing laryngotracheobronchitis have been previously reported (Table 2). Both these patients presented with cough and fever. Notably, case 2 was also that of a child, and in addition to cough and fever, obvious hoarseness was also present. Hence, in patients with M. pneumoniae pneumonia, having obvious hoarseness, acute pseudomembranous necrotizing laryngotracheobronchitis should be considered during the differential diagnosis.
As acute pseudomembranous necrotizing laryngotracheobronchitis is relatively rare, the underlying mechanisms remain unclear. Accumulating data show that the initiating factors of acute pseudomembranous necrotizing laryngotracheobronchitis are viral infections. Subsequent bacterial infections are mostly caused by the Gram-positive bacteria (eg, Staphylococcus aureus) [2,3,4]. Although leukotoxin crucially contributes to Staphylococcus aureus-induced necrotizing laryngotracheobronchitis and pneumonia, owing to the destruction of the airway epithelial cells and lungs the mechanisms underlying M. pneumoniae-induced necrotizing laryngotracheobronchitis and pneumonia have not yet been reported. These may possibly be related to the direct destruction of the trachea and bronchial mucosa by M. pneumoniathe toxic changes in tracheal epithelial cells, and excessive immune responses of the body, similar to the mechanism of action of M. pneumoniae-associated necrotizing pneumonia .
Although three patients with M. pneumoniae Infection-related acute pseudomembranous necrotizing laryngotracheobronchitis have been reported to recover, necrotizing tissue, phlegm plugs, and pseudomembrane may fall off and block the airway, thereby causing a critical situation. In patients with M. pneumoniae Infections, recognizing the complications outside the lung injury is equally essential in addition to the lung injury. For acute pseudomembranous necrotizing laryngotracheobronchitis, bronchoscopy is a crucial method to diagnose and remove pseudomembranes, thereby alleviating airway obstruction [4, 20]. All three cases of M. pneumoniae Infection-related acute pseudomembranous necrotizing laryngotracheobronchitis patients have reportedly undergone bronchoscopy, which further confirmed the diagnosis and were treated by the removal of the pseudomembranes and for BAL. In children with M. pneumoniae infection and unexplained symptoms (eg, unrelieved hoarseness, persistent fever), bronchoscopy should be performed for further investigation. Removing the pseudomembranes and washing out the bronchial lumen may improve their condition.
Recently, it has been proposed that the severe inflammatory reactions after M. pneumoniae Infection are caused mainly by abnormal immune responses. Therefore, in patients who rapidly progress in the acute stage, severe cases, and those with extrapulmonary complications, early application of glucocorticoids should be considered apart from macrolides administration, to quickly relieve symptoms, shorten the course of the disease, and increase the cure rate . As in the two previously reported cases, methylprednisolone (1 mg/kg/day) was administered to our patient on the second day of admission. The fever, cough, and hoarseness of the child were significantly relieved.
In conclusion, in M. pneumoniae pneumonia patient with obvious hoarseness, acute pseudomembranous necrotizing laryngotracheobronchitis should be considered in the differential diagnosis; bronchoscopy and BAL should be performed early during the course of treatment. Besides macrolide antibiotics, glucocorticoids should be administered in these refractory cases.