Is the clinical significance of community-acquired pneumonia (CAP) visualised on CT scans only the same as of CAP visualised on chest x-rays?
EJRC Article Review
The clinical significance of radiological signs of pneumonia visualised only on CT imaging is largely unknown, which creates uncertainty about the appropriate management: Should the management approach be according to the same principles as for pneumonia that has been identified on chest radiography? Or is CT-only pneumonia a distinct, less severe disease that requires a different management approach?
In order to assess the clinical significance of CAP visualised only on CT scans, Upchurch et al. conducted an analysis  nested within the CDC EPIC study , a prospective multicentre active surveillance study of adult hospitalised patients with CAP.
The cohort consisted of 2,251 adults hospitalised with CAP; 2,185 patients (97%) had CAP evident on chest radiography, whereas 66 patients (3%) had CT-only visualised CAP. Overall, the group of CT-only CAP had a clinical profile similar to the group of chest radiography visualised CAP, including: comorbidities, vital signs, hospital length of stay, prevalence of viral (30% vs 26%) and bacterial (12% vs 14%) pathogens, ICU admission rate (23% vs 21%), use of mechanical ventilation (6% vs 5%), septic shock (5% vs 4%), and in-hospital mortality (0 vs 2%).
The authors claimed that the findings support the management of CT-only CAP according to the same principles used for chest radiography visualised CAP. Additionally, they claimed that CT-only CAP could be associated with significant physiological abnormalities and morbidity. Hence, they suggested the use of CT scan to evaluate for pneumonia when the clinical presentation is suggestive, but an initial chest radiograph does not demonstrate radiological signs of pneumonia, and the identification of pneumonia as the cause of clinical symptoms is important.
Although, patients with CT-only CAP were largely similar to those with chest radiograph evident CAP, the authors pinpointed some potential differences that need further exploration in future studies, such as, CT-only CAP being more common in obese patients, having lower PCT levels, and having a higher prevalence of human rhinovirus detection. Notwithstanding, it was highlighted that the incidence of bacterial pathogen detection was similar between the two groups and also, the combination of chest radiography and PCT determination did not identify all bacterial CAP cases.
The main limitations of the study were the following:
-Only 1/3 of the cohort underwent chest CT. CT imaging use was determined by the treating clinicians; patients with chest pain, shortness of breath, and haemoptysis were more likely to undergo chest CT, therefore, the results may not be generalisable to patients whose clinicians are not concerned enough to order chest CT imaging.
-Patients with clinical evidence of pneumonia and no evidence on chest radiograph that did not undergo chest CT were not included in the study; if chest CT was systematically done, additional cases of CT-only CAP might had been discovered.
– Although this is the largest study to date assessing CT-only CAP, the sample size was not large enough for multivariable analyses and no robust comparison of mortality was possible.
– The antibiotic use in nearly all patients precluded the evaluation of antibiotics impact on clinical outcomes.
– Only hospitalised patients with CAP were included and thus the generalisability to outpatients is unknown.
Take home message
The findings of this large prospective study support that adult hospitalised patients with CAP visualised only on CT scan should be managed according to the same principles as for CAP evident on chest radiographs, including the selection of empirical antibiotics and site of care. However, further studies are warranted to provide more robust and generalisable results.
Article review for the ESICM Journal Review Club on behalf of the Pneumonia-WG provided by Dr. Despoina Koulenti and Dr Evdoxia Tsigou
- Upchurch CP, Grijalva CG, Wunderink RG, Williams DJ, Waterer GW, Anderson EJ, Zhu Y, Hart EM, Carroll F, Bramley AM, Jain S, Edwards KM, Self WH. Community-Acquired Pneumonia Visualised on CT Scans but Not Chest Radiographs: Pathogens, Severity, and Clinical Outcomes. Chest. 2017 Aug 9. pii: S0012-3692(17)31392-2. doi: 10.1016/j.chest.2017.07.035. [Epub ahead of print] https://www.ncbi.nlm.nih.gov/pubmed/28802696
- Jain, S., Self, W.H., Wunderink, R.G. et al. Community-acquired pneumonia requiring hospitalisation among US adults. N Engl J Med. 2015; 373: 415–427 http://www.nejm.org/doi/full/10.1056/NEJMoa1500245