Abstract
BackgroundChest radiographs are used for diagnosis and severity assessment in tuberculosis (TB). The extent of disease as determined by smear grade and cavitation as a binary measure can predict 2-month smear results, but little has been done to determine whether radiological severity reflects the bacterial burden at diagnosis.MethodsPre-treatment chest x-rays from 1837 participants with smear-positive pulmonary TB enrolled into the REMoxTB trial (Gillespie et al., N Engl J Med 371:1577–87, 2014) were retrospectively reviewed. Two clinicians blinded to clinical details using the Ralph scoring system performed separate readings. An independent reader reviewed discrepant results for quality assessment and cavity presence. Cavitation presence was plotted against time to positivity (TTP) of sputum liquid cultures (MGIT 960). The Wilcoxon rank sum test was performed to calculate the difference in average TTP for these groups. The average lung field affected was compared to log 10 TTP by linear regression. Baseline markers of disease severity and patient characteristics were added in univariable regression analysis against radiological severity and a multivariable regression model was created to explore their relationship.ResultsFor 1354 participants, the median TTP was 117 h (4.88 days), being 26 h longer (95% CI 16–30, p < 0.001) in patients without cavitation compared to those with cavitation. The median percentage of lung-field affected was 18.1% (IQR 11.3–28.8%). For every 10-fold increase in TTP, the area of lung field affected decreased by 11.4%. Multivariable models showed that serum albumin decreased significantly as the percentage of lung field area increased in both those with and without cavitation. In addition, BMI and logged TTP had a small but significant effect in those with cavitation and the number of severe TB symptoms in the non-cavitation group also had a small effect, whilst other factors found to be significant on univariable analysis lost this effect in the model.ConclusionsThe radiological severity of disease on chest x-ray prior to treatment in smear positive pulmonary TB patients is weakly associated with the bacterial burden. When compared against other variables at diagnosis, this effect is lost in those without cavitation. Radiological severity does reflect the overall disease severity in smear positive pulmonary TB, but we suggest that clinicians should be cautious in over-interpreting the significance of radiological disease extent at diagnosis.
Highlights
Chest radiographs are used for diagnosis and severity assessment in tuberculosis (TB)
Murthy et al BMC Medicine (2018)6:73. Since their introduction in routine clinical practice in the 1920s, chest radiographs have been used as a primary tool to diagnose and manage pulmonary tuberculosis (PTB) [1,2,3]
In 2010, Ralph et al [12] created a simple validated scoring system from findings that the proportion of lung fields affected by disease at diagnosis of PTB was associated with a greater acid fast bacilli (AFB) smear grade and that the presence of cavitation, along with the percentage of lung field affected on chest x-ray (CXR), predicted 2-month smear positivity on treatment
Summary
Chest radiographs are used for diagnosis and severity assessment in tuberculosis (TB). The extent of disease as determined by smear grade and cavitation as a binary measure can predict 2-month smear results, but little has been done to determine whether radiological severity reflects the bacterial burden at diagnosis Since their introduction in routine clinical practice in the 1920s, chest radiographs have been used as a primary tool to diagnose and manage pulmonary tuberculosis (PTB) [1,2,3]. In 2010, Ralph et al [12] created a simple validated scoring system (using a score out of 140) from findings that the proportion of lung fields affected by disease at diagnosis of PTB was associated with a greater acid fast bacilli (AFB) smear grade and that the presence of cavitation (but not number or size of cavitation), along with the percentage of lung field affected on CXR, predicted 2-month smear positivity on treatment This has gained some currency in studies describing radiological severity [13,14,15] and in a subsequent study that validated this approach [16]
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