A Few Cases of Increased FDG Uptake on 18F-FDG PET/CT in Residual Lesions of Tuberculosis at the Time of Treatment Completion

Abstract

Introduction: The presence of radiographic lesions such as cavity is one of the risk factors for treatment failure or relapse of pulmonary tuberculosis (TB). A functional imaging technique that monitors glucose metabolism in tissues, 18F-fluorodeoxyglucose positron emission/computed tomography (18F-FDG PET/CT) has been reported recently to detect metabolic activity of TB lesions in the lung which could reveal therapeutic response in early time point. Measuring of FDG uptake at the time of treatment completion could give us information about the association of increased FDG uptake with risk of relapse afterwards. CASE PRESENTATION: Five cases of pulmonary TB had been treated with first-line anti-TB drugs (isoniazid, rifampicin, ethambutol, and pyrazinamide). 4 males and a female, age ranged from 31 to 64 years old are all new TB patients with no history of previous treatment. At the time of diagnosis sputum smears for acid-fast bacilli(AFB) were positive as were cultures for Mycobacterium Tuberculosis. All of them have no co-morbidity of diabetes or cancer. Their chest x-ray showed cavitary lesions in upper lung field in two patients. Their compliance of treatment was good with no interruption of medication by any reasons. Sputum microbiologic tests converted to negative and treament completed after 6 months or 9 months in total. They checked 18FFDG PET/CT at the time of treatment completion. 4 out of 5 showed increased FDG uptake of residual lesions especially in cavity wall or residual parenchymal lesions. DISCUSSION: Tuberculosis (TB) needs very long duration of combination antibiotic therapy required to achieve relapse-free cure. The World Health Organization recommends the standard treatment length as 6 months for drug susceptible TB and 20 months for multidrug-resistant and extensively drug-resistant TB (M/XDR-TB). The optimal duration for treatment of TB likely differs between individuals and depends on a variety of variables, such as the extent of the disease. Personalization of the duration of treatment for TB, especially for patients with M/XDR-TB, would be desired but there has been little information of biomarkers to decide for relapse-free cure. In recent literatures, 18F-FDG PET/CT correlates with treatment outcome in MDR-TB and could be useful as an early therapeutic marker. Given that the increased FDG uptake shows active granulomatous inflammation of TB lesions, 18F-FDG PET/CT at the time of scheduled completion could be a marker to predict the risk of relapse. Conclusions: More study is needed to evaluate the association of increased FDG uptake of residual lesions in the lung at treatment completion with the risk of relapse since 18F-FDG PET/CT at the time of scheduled completion could be used as a decision maker of personalized treatment duration to minimize the risk of relapse in the future, especially for the treatment of drug resistant TB.