Fluorodeoxyglucose Positron Emission Tomography Imaging in Pneumocystis jiroveci Pneumonia

Background and Procedure

We describe a case of a 48-year-old man with pyrexia of unknown origin (PUO), who is a known case of multiple myeloma on immunosuppressive therapy, with remission of disease on recent bone marrow examination. This case presented with dry cough and fever over 4 weeks (100°F–102°F) and had an oxygen saturation of 97% on ambient air. The blood tests apart from mild leukopenia were fairly unremarkable. The chest radiography revealed subtle bilateral lung ground-glass opacities and referred for fluorodeoxyglucose positron emission tomography (FDG-PET)/computed tomographic (CT) scan to rule out the cause. The FDG-PET scan [Figure 1] revealed diffuse increased metabolic activity in bilateral lungs; the corresponding fused high-resolution CT (HRCT) images showed the acute lung changes in the form of hypermetabolic ill-defined confluent ground-glass opacities with interstitial thickening and crazy paving appearance near completely involving bilateral lungs along with mild bronchial and bronchiolar dilatation [Figure 2]. The imaging was suggestive of acute atypical pneumonia which was further investigated by bronchoalveolar lavage cytological examination and culture which demonstrated Pneumocystis jiroveci.

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Figure 1 Whole-body fluorodeoxyglucose positron emission tomography scan maximum intensity projection image reveals diffuse increased metabolic activity in bilateral lungs with physiological fluorodeoxyglucose uptake in rest of the visualized body

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Figure 2 High-resolution computed tomography (left), and fused fluorodeoxyglucose positron emission tomography and high-resolution computed tomography (right) images reveals hypermetabolic ill-defined confluent ground-glass opacities with interstitial thickening near completely involving bilateral lungs

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Pneumocystic jiroveci pneumonia (PJP), is also known as pneumocystic pneumonia or formerly pneumocystic carinii pneumonia, is caused by the ubiquitous unicellular eukaryote, P jiroveci, which is a rare cause of infection in the general population, but it is a more frequent cause of morbidity and mortality in immunocompromised persons who are especially with HIV AIDS, postorgan-transplant recipients, and those receiving long-term cytotoxic or steroid therapy, hematological malignancies, as well as other malignancies.[1] PJP is classified as a fungal pneumonia but does not respond to antifungal therapy. These patients have a long clinical course over months to years, with stable symptoms and radiographic abnormalities corresponding to pathologic findings of traction bronchiectasis, honeycombing, and interstitial fibrosis.

In a study of 105 pneumocystic pneumonia immunocompromised patients, chest radiographic findings were divided into three stages: early stage; normal or nearly normal chest radiograph, mid-stage; bilateral pulmonary infiltrates, and late stage; bilateral pulmonary consolidation. Chest HRCT findings were also divided into three stages: early stage; bilateral diffuse ground-glass opacity, mid-stage; bilateral diffuse ground-glass opacity with patchy consolidations, and late stage; bilateral diffuse consolidation).[2]

Conclusion

FDG-PET/CT imaging is a very sensitive diagnostic modality for the evaluation of fever of unknown origin by facilitating anatomical localization of focally increased FDG uptake and thereby guiding further diagnostic tests to achieve a final diagnosis.[3] Few studies suggest that FDG-PET scan have an important role to play in the diagnosis and monitoring treatment response of pneumocystic pneumonia in the immunocompromised patients.[4]