Nuclear medicine imaging in tuberculosis using commercially available radiopharmaceuticals

In this paper, data available on nuclear medicine imaging using commercially available radiopharmaceuticals for the differentiation, staging, and prediction or assessment of the response to treatment in tuberculosis (TB) are reviewed. Limited available studies suggest that single photon emission computed tomography (SPECT) using either 201Tl, 99mTc-sestamibi, or 99mTc-tetrofosmin is accurate (≥85%) and has a high negative predictive value (≥90%) for the differentiation of TB from carcinoma in patients presenting with a solitary pulmonary nodule (SPN). The criteria for detection of TB on 201Tl SPECT are nondepiction of the suspicious lesion in the delayed image or a negative retention index [washout on the delayed images (3–4 h postinjection) vs. the early image (5–15 min postinjection)] and a comparable-to-background uptake on 99mTc-sestamibi or 99mTc-tetrofosmin SPECT. Another SPECT tracer of potential interest for the differentiation of TB from malignant SPN that warrants further exploration, is N-isopropyl-p-[123I]iodoamphetamine (123I-IMP). In contrast, 18F-fluorodeoxyglucose (18F-FDG) PET is unable to differentiate malignancy from TB and thus cannot be used as a tool to reduce futile biopsy/thoracotomy in these patients. A limited number of studies have reported on the potential of nuclear medicine imaging in assessment of the extent of disease in patients with extrapulmonary TB using 67Ga-citrate SPECT and 18F-FDG PET, respectively. 67Ga-citrate SPECT was shown to be as sensitive as bone scintigraphy for the detection of bone infection and was found to be complementary to computed tomography (CT) imaging. 18F-FDG PET was found to be significantly more efficient when compared with CT, respectively, in over half of patients for the identification of sites of lymph node involvement that were missed by CT and often the only sites of extrapulmonary TB identified. Unfortunately, 18F-FDG PET findings did not lead to alterations in treatment planning in any of the patients under study. Additional studies confirming these findings are urgently required. Similar to the setting of SPN, 18F-FDG PET cannot differentiate malignant lymph node involvement from lymph node involvement by TB. These results and the recent findings of Demura and colleagues using 18F-FDG PET further suggest that nuclear medicine imaging techniques could be used for the evaluation of therapeutic response. Prospective studies, focusing on specific subgroups of patients in whom such an imaging approach might be clinically relevant, for example in multidrug-resistant TB patients, are warranted. In acquired immunodeficiency syndrome patients, 67Ga scintigraphy proved to be a reliable and sensitive method for the primary detection and follow-up of opportunistic pneumonias, including TB. Combining 201Tl scintigraphy with 67Ga scintigraphy was shown to increase the specificity for both pulmonary and extrapulmonary TB, which is a 67Ga(+) and 201Tl(-) mismatch pattern in acquired immunodeficiency syndrome patients that is specific for mycobacterial infections. Finally, the results obtained using both SPECT and PET indicate that nuclear medicine could be an important noninvasive method for the determination of disease activity, detection of extrapulmonary TB, and determination of response to therapy.