Role for Positron Emission Tomography-Computed Tomography in Melioidosis

Sir,

We read with interest the case series, “18-Fluorine-Fluorodeoxyglucose Positron Emission Tomography-Computed Tomography (PET-CT) in the Evaluation of the Great Masquerader Melioidosis: A Case Series,” by Kulkarni et al., published in the July–September issue of Indian Journal of Nuclear Medicine.[1] The authors have discussed the diagnostic utility of PET-CT in two patients with pyrexia of unknown origin (PUO), an indication for which PET-CT has been discussed in previously published literature.[234] The two patients were subsequently diagnosed with melioidosis. The authors have performed PET-CT before achieving a diagnosis of melioidosis, rather than part of evaluation of proven melioidosis, as the title suggests. However, we believe that the authors have raised an interesting point and led us to consider and propose PET-CT as an ideal investigation in the evaluation of proven melioidosis, with the illustration of a patient who recently presented to us.

A 34-year-old male with no significant history presented with 5 days of fever, cough, purulent sputum, and dyspnea. He had fever, tachycardia, tachypnea with room air peripheral saturation of 92%, and bilateral basilar crackles on chest auscultation. Abdominal and neurological examination was normal. Apart from anemia and leukocytosis, the blood hematology and biochemistry were normal. Serology for human immunodeficiency virus and scrub typhus were negative. Peripheral smear did not reveal malarial parasites. Chest radiograph [Figure 1a] showed bilateral lung nodules. He was diagnosed with community-acquired pneumonia, and after sending sputum and blood cultures, he was initiated on intravenous (IV) ceftriaxone and admitted in the ward. His sputum and blood culture [Figure 1b and c] confirmed Burkholderia pseudomallei, following which he was switched to IV ceftazidime. PET-CT was performed, which showed bilateral lung nodules with mild FDG uptake, some with feeding vessel sign, and mediastinal lymphadenopathy, with no evidence of uptake elsewhere [Figure 1d]. He improved clinically with 2 weeks of IV ceftazidime and was discharged on oral cotrimoxazole for 3 months. Chest radiograph 3 months later showed complete resolution [Figure 1e].

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Figure 1 (a) Chest radiograph showing bilateral lung nodules. (b) Gram stain of sputum sample showing Gram-negative rods with beaded ends. (c) Blood culture on MacConkey agar at 72 h of incubation showing colonies with dry, wrinkled, and metallic sheen appearance suggestive of Burkholderia pseudomallei. (d) Positron-emission tomography-computed tomography scan of thorax at the level of bifurcation of main pulmonary artery showing bilateral variable sized random lung nodules, some with feeding vessel sign and mediastinal lymphadenopathy. (e) Chest radiograph after 3 months of eradication therapy

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Although melioidosis commonly presents with pulmonary involvement, it can involve various other organs, including liver, spleen, lymph nodes, bones, joints, skin, and the central nervous system.[56] Treatment of meloidosis consists of a 2–4-week intensive phase to treat bacteremia, followed by an eradication phase to eliminate any residual focus of bacteria. The duration of this eradication phase is determined by extent of multifocal involvement and evidence of deep seated infection. The failure of eradication may lead to a future relapse.[7] Hence, it becomes important to image various organ systems, including abdomen and the axial and appendicular skeleton, to identify disease involvement elsewhere. Such a multimodality imaging approach, which may include an ultrasound of abdomen and magnetic resonance imaging of spine, may be cumbersome and can be replaced by a whole-body (PET-CT) scan, which can additionally detect disease in less common sites.

The use of PET-CT scan in the management of melioidosis is infrequently reported and was reviewed by the authors. Table 1 summarizes the available literature.[1891011] The indications for PET-CT in the reviewed publications were varied and included (1) to identify possible malignancy or metastases in a patient with clinical suspicion of malignancy,[81011](2) to look for other sites of organ involvement in a patient with blood culture-proven melioidosis,[9](3) in the evaluation of PUO and to identify an appropriate diagnostic investigation,[1] and (4) in the follow-up of patients with melioidosis and multiple site involvement to assess response to treatment.[810] Except for three, all the patients reported above had chronic symptoms and were being evaluated for possible malignancy or PUO. Two patients, who had symptoms for 4 days and 2 weeks, respectively, had thoracic radiology that was suspicious for malignancy and hence were subjected to PET-CT.[1011] Only in one patient, who had a subacute presentation, PET-CT was done after a positive culture of melioidosis, with the aim of searching for disease involvement in other sites, similar to our indication.[9] We believe that this indication has its benefits in avoiding multiple system-specific imaging, helps identify asymptomatic disease sites that may be responsible for future relapse if left untreated, and thus helps decide on duration of eradication therapy.[8]