Can FDG PET/CT Be Used to Optimize the Treatment of Patients with Pulmonary Tuberculosis?

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Introduction: The treatment of pulmonary tuberculosis is long due to the slow-growing nature of Mycobacterium tuberculosis (MTb). At the end of a standard course of antituberculous treatment (ATT), some patients still harbor slow-growing MTb (sgMTb) in their lesions, which are responsible for relapse. These sgMTb are nonculturable and are difficult to detect. We investigate the utility of end-of-treatment [¹⁸F]F-FDG PET/CT to differentiate patients with sterilizing cure versus those with sgMTb who are at risk for relapse.

Methods: We prospectively recruited patients who had a standard course of ATT. All patients underwent [¹⁸F]F-FDG PET/CT within 2 weeks of completing ATT. We determined the presence of residual metabolic activity (RMA), which is FDG uptake in the lungs above mediastinal background activity on the [¹⁸F]F-FDG PET/CT. Patients were classified as having RMA or complete metabolic response (CMR) to ATT. All patients were subsequently followed up after completing [¹⁸F]F-FDG PET/CT imaging for relapse. Confirmatory bacteriologic testing was performed in patients with clinical suspicion of relapse. In those who relapsed, a repeat FDG PET/CT imaging was subsequently performed.

Results: We studied 75 patients including 50 HIV-infected individuals with a mean age of 36.09 ± 10.49. The median CD4 count among HIV-infected patients was 255 cells/mm³ (IQR: 147– 448). HIV viral load was 12,497 copies/mL (IQR: 158–3,8841). HIV-infected patients had lower hemoglobin levels (13.07 ± 1.78 g/dL vs. 14.24 ± 2.07, p = 0.021) and higher C-reactive protein levels (5.70 vs. 1.20, p = 0.001) compared with HIV-uninfected patients. All other baseline clinical and demographic characteristics were not significantly different between the groups. Forty-one patients had RMA and its incidence was not significantly different between HIV-infected and uninfected patients (p = 0.101). Thirty-four patients demonstrated complete metabolic response (CMR) to ATT. No tuberculosis relapse was demonstrated in those with CMR. In the RMA group, three patients (7.3%) relapsed on follow-up. Relapse was confirmed bacteriologically in all the three patients. Repeat [¹⁸F]F-FDG PET/CT imaging at the time of clinical relapse demonstrated the persistence of RMA in the same lung regions in all three patients.

Conclusion: FDG PET/CT imaging demonstrates a high prevalence of RMA among patients treated with a standard course of ATT for PTB, with a similar incidence between HIV-infected and uninfected patients. CMR on posttreatment [¹⁸F]F-FDG PET/CT is consistent with sterilizing a cure for pulmonary tuberculosis. Patients with RMA on posttreatment [¹⁸F]F-FDG PET/CT are at risk for tuberculosis relapse. These results show the potential of [¹⁸F]F-FDG PET/CT for use as a noninvasive biomarker for drug development and in investigating shorter ATT regimens.

Publication History

Article published online:
25 May 2023