Does Mycoplasma pneumoniae Leave Long-Term Structural Changes?
Abstract & Commentary
Synopsis: Although Mycoplasma pneumoniae is characterized by a relatively mild clinical course and is often a self-limited infection, this study indicates that more than one-third of children showed abnormality on HRCT from 1.0-2.2 years after the respiratory infection.
Source: Kim CK, et al. Late abnormal findings on high-resolution computed tomography after Mycoplasma pneumoniae. Pediatrics 2000;105:372-378.
Mycoplasma pneumoniae accounts for as many as 20% of all cases of community-acquired pneumonia in the general population and up to 50% in closed populations. The clinical course is typically mild and self-limited with uneventful recovery. This study was conducted to investigate by means of high-resolution computed tomography (HRCT), the long-term pulmonary structural abnormalities, and also to identify risk factors that might increase the likelihood of developing sequelae.
The study examined with HRCT a group of children who had Mycoplasma pneumoniae (n = 38) and a group with upper respiratory tract infection due to Mycoplasma (n = 17). The HRCT was performed at an interval of 1.0-2.2 years (mean, 1.5 yrs) after the infection. HRCT scans were obtained at 10-mm intervals with the subjects in the supine position starting from the aortic arch level to the diaphragm using 120 kVp and 320 mAs. In children older than 5 years of age, the scans were obtained while they held their breath in full inspiration.
Pulmonary abnormalities were present on HRCT in 14 (36.8%) of the pneumonia group. The observations were mosaic perfusion (n = 12; 31.6%), bronchiectasis (n = 10; 26.3%), bronchial wall thickening (n = 4; 10.5%), and decreased pulmonary vascularity (n = 1; 2.6%). Nine (31%) of the 29 patients who also underwent expiratory HRCT had air trapping. All of the patients with air trapping had other abnormal findings. To assess possible risk factors, the pneumonia group was classified into two groups based on the presence or absence of abnormal HRCT findings. The significant intergroup differences were age at the time of pneumonia; the abnormal HRCT group was 5.3 ± 2.0 years vs. normal HRCT group aged 7.7 ± 3.4 years. The interval between pneumonia and HRCT was not different between the two groups.
The peak antibody titer in the abnormal group was 1:7943 vs. 1:3093 in the normal group.
The abnormal findings on HRCT included mosaic perfusion, bronchiectasis, bronchial wall thickening, air trapping, and Swyer-James syndrome. Mosaic perfusion and geographic areas of increased and decreased lung attenuation were the most frequent findings. The appearance is thought to be caused by decreased perfusion of areas with bronchiolar obstruction and flow redistribution. Mycoplasma pneumoniae may be more serious in children than has been previously recognized and may be an important cause of small airway obstruction.
Comment by Beverly P. Wood, MD
Since Mycoplasma pneumoniae is a frequent cause of lower respiratory infection, a study indicating that there are significant long-term pulmonary structural implications is important to recognize. It is possible that Mycoplasma pneumoniae in a child is a more serious disease than recognized. In children with known Mycoplasma infections, two factors of particular importance are young age and the presence of higher peak antibody titers. The height of the antibody response may also indicate a more severe infection. It is possible that Mycoplasma pneumoniae is an important contributor to later small airways disease and chronic bronchial changes. The effect may be greater on the growing and developing lung. A comparison of pulmonary function of these two groups, such as an FEV1, would be of interest to identify the accompanying functional effects. Correlating the clinical defect and the visual changes would be importanat. For radiologists, the association of Mycoplasma pneumoniae with significant long-term HRCT abnormality is an association to which we should be attentive when assessing young children with small airway disease.
Reference
1. Todisco T, et al. Viral and Mycoplasma pneunomiae pneumonias in school-age children: Three-year follow-up of respiratory function. Pediatr Pulmonol 1989; 6:232-236.
What was a frequent HRCT change seen in children after Mycoplasma pneumoniae?
a. Patches of atelectasis
b. Mosaic perfusion
c. Emphysema
d. Bronchial plugs
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