Journal of Postgraduate Medicine Medknow Publications and Staff Society of Seth GS Medical College and KEM Hospital, Mumbai, India ISSN: 0022-3859 EISSN: 0972-2823 Vol. 56, Num. 3, 2010, pp. 219-221

Journal of Postgraduate Medicine, Vol. 56, No. 3, July-September, 2010, pp. 219-221

Case Snippet

FDG-PET/CT in diagnosis and early response evaluation of extra-pulmonary tuberculosis in a patient with aplastic anemia

Harisankar CNB, Mittal BR, Bhattacharya A, Singh B

Department of Nuclear Medicine & PET, Postgraduate Institute of Medical Education and Research, Chandigarh – 160 012, India

Correspondence Address: Dr. Bhagwant Rai Mittal, Department of Nuclear Medicine & PET, Postgraduate Institute of Medical Education and Research, Chandigarh – 160 012, India, brmittal@yahoo.com

Code Number: jp10063

PMID: 20739773

DOI: 10.4103/0022-3859.68639

Infections remain one of the leading cause of fever of unknown origin (FUO). ^[1] In addition to morphologic imaging, a variety of radionuclide imaging techniques are being used for imaging inflammation and infection (67-Gallium, Fluoro-deoxy glucose (FDG), labeled leukocytes, immunoglobulins, antibodies, antibiotics etc). ^[2] FDG-positron emission tomography (PET) has been shown to be helpful in a significant number of patients with FUO. ^[3] We report a case highlighting the utility of FDG PET/Computed tomography (CT) in diagnosis and early response monitoring of extra-pulmonary tuberculosis in a case of idiopathic aplastic anemia post bone marrow transplantation (BMT). This report highlights the fact that FDG-PET has a value in localizing infectious foci in complicated cases and could serve as a baseline for their early response evaluation. Further, information from PET allowed the interventionist to target a safer and easily accessible site for pathological confirmation.

Ten months post BMT for aplastic anemia, a 35-year-old female presented with intermittent high-grade fever and chills. Complete hemogram was unremarkable except for the anemia. The peripheral smear showed hypochromic RBCs. Erythrocyte sedimentation rate was raised (66 mmHg for first hour). Chest X-ray and sputum examination were normal. Widal test, blood and urine cultures were negative. Chest CT showed mediastinal lymphadenopathy without any significant parenchymal changes. She was subjected to a whole body FDG-PET/CT for localization of source of infection. Whole body PET/CT scan was performed as per the following protocol. After 6 h of fasting, the patient was administered 370 MBq of F-18 FDG. Positive oral contrast (1700 ml of 2% solution of urograffin) was administered over a period of one hour followed by additional 300 ml while the patient was positioned for imaging. No intravenous contrast was used. After 60 min of waiting period, the images were acquired in a full-ring PET scanner in 3-D mode (Discovery STE 16, GE Healthcare, Melwaukee, USA). The CT part of the PET/CT was acquired with the following parameters: Voltage 140 kVp, tube current 240mA. Whole body PET was performed from the skull base to the mid-thigh in six bed positions, each of 2 min duration. Attenuation correction was performed using the CT data and reconstruction of the PET data was performed using iterative reconstruction.

Intense FDG uptake was noted in the right lower paratracheal and sub-carinal lymph nodes, L2 vertebra and right sacro-iliac joint with evidence of cortical destruction. Lungs were morphologically normal with no abnormal FDG uptake. Physiological FDG uptake was noted in the brain, myocardium, breasts, liver, bone marrow, bowel and urinary tract. Focal FDG uptake noted in the right carotid artery and left subclavian artery was related to atherosclerosis while L3 facet joint uptake represented degenerative changes. Considering the involvement of lymph nodes, bone and joint, in a tuberculosis endemic country, a diagnosis of tuberculosis was considered. CT-guided fine needle aspiration cytology (FNAC) from the L2 vertebra confirmed the presence of tuberculous bacilli. Patient was started on anti-tubercular treatment (ATT). Repeat study after eight weeks of therapy showed mild FDG uptake in the mediastinal lymph nodes, L2 vertebra and right sacro-iliac joint. However, there was approximately 60% reduction in the FDG uptake in these sites indicating good ongoing metabolic response to ATT. The L2 vertebra and sacro-iliac joints showed sclerotic changes on CT suggesting healing of the lesions. The patient is currently continuing the full course of ATT. [Figure - 1] and [Figure - 2] represent changes in FDG uptake from baseline to after eight weeks of ATT.

Studies have evaluated gallium scintigraphy in the monitoring of tuberculosis. ^[4] A few studies have used FDG in the monitoring of pulmonary mycobacteriosis and tuberculoma. ^[5],[6] However, these studies have performed the follow-up imaging at third month or at completion of therapy. ^[6] To the best of our knowledge, this is the first time that response to treatment of tuberculosis has been demonstrated at eight weeks post therapy. This would have potential implications in identifying cases of drug-resistant tuberculosis and tailoring their treatment. Adequate patient care by early diagnosis of disease is the ultimate aim of technological advances in imaging. We have highlighted the fact that PET would be invaluable in not only localizing but also monitoring tuberculosis as early as eight weeks post start of therapy.

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