¹⁸F-FDG PET/CT in extra-pulmonary tuberculosis - Role in initial evaluation and responseassessment

Objectives: Tuberculosis is an endemic disease in the Asian population, accounting for high morbidity, mortality and significant risk of transmission from the infected individuals. ¹⁸F-FDG PET/CT has the advantage of a whole-body scanning at a single setting which provides useful information about the disease burden in whole and thus can guide appropriate treatment. This study was performed to evaluate the utility of ¹⁸F-FDG PET/CT in the initial evaluation and response assessment of patients with extra-pulmonary tuberculosis.

Methods: 93 patients (42 women, 51 men) diagnosed with extra-pulmonary tuberculosis (with histologic/ microbiological confirmation) were prospectively enrolled in the study prior to the initiation of treatment. All the patients underwent ¹⁸F-FDG PET/CT (diagnostic contrast-enhanced CT) at baseline and follow-up scans at 2 months & at completion of therap. A total of 168 PET/CT studies were performed, as few patients lost to follow up. Follow-up scans, post anti-tubercular treatment, were categorized as complete metabolic response (CR) - no abnormal pathologic FDG uptake noted in the scan, residual disease (RD) - persistent lesions without any obvious new lesions, disease progression (DP) - new lesions compared to the baseline scan. Clinical assessment of all the patients was done at last follow-up.

Results: ¹⁸F-FDG PET/CT performed at baseline was positive in all 93 patients (100%) with detection of lesions at 176 sites. Most common sites of involvement were lymph nodes (78/176; 44.3%) followed by central nervous system (CNS) lesions (47/176; 26.7%). Vertebral (Pott’s spine), splenic, ocular, laryngeal and other soft tissue involvement by TB was also noted. 2^nd follow-up scan was performed in 47 patients. 10/47 patients (21.2%) were categorized as CR, 34/47 (72.3%) were RD while 3/47 (6.4%) were categorized as DP. 3^rd follow-up scan was performed in 28 patients. 8/28 (28.6%) showed CR, out of which 3 maintained their CR status from the 2^nd scan, while 5 with previous RD, showed CR. 15/28 (53.6%) patients showed RD, the same status as in the 2^nd scan. 5/28 (17.8%) showed DP, out of which three were previously categorized as DP and two as RD in the 2^nd scan. Additional drugs were added in the anti-tubercular therapy in the patients with DP, while the standard anti-tubercular therapy was continued in the patients with RD. Last follow-up with clinical assessment was done at 22 ± 6.8 months (mean ± SD). 12/93 patients (12.9%) expired during the study period; 4/12 expired after the first scan, 3/12 had DP and 5/12 had RD on follow-up PET/CT. All four patients who expired after the first scan had multiple CNS-TB lesions. Out of all the follow-up categories, DP had the highest mortality of 60%. Anti-tubercular treatment was continued in the RD and DP category patients and they were kept on regular follow-up. All patients categorized as CR in the follow-up scans, maintained remission at the last follow-up and were declared as cured.

Conclusions: F-18 FDG PET/CT showed multiple extra-pulmonary sites on baseline scan apart from initial clinical referral. Early follow-up PET/CT studies could categorize patients into responders and non-responders as well as were able to predict the prognosis. These findings support the role of 18F-FDG PET/CT in the management of patients with extra-pulmonary tuberculosis, in the initial evaluation as well as in monitoring response to treatment.