18F-FDG PET/CT for the Assessment of Disease Extension and Activity in Patients With Sarcoidosis: Results of a Preliminary Prospective Study

Utility of FDG-PET-CT scanning in assessing the extent of disease activity and response to treatment in sarcoidosis

BACKGROUND

Radionuclide imaging modalities have increasingly been evaluated in the assessment of organ involvement in sarcoidosis. Fluoro-deoxyglucose positron emission tomography-computed tomography (FDG-PET-CT) scanning has received increasing attention in the recent years. The aim of our study was to evaluate the utility of FDG-PET-CT in determining the extent of organ involvement and disease activity in patients of sarcoidosis and to assess its utility in the evaluation of response to therapy. The secondary objective was to compare the agreement between clinical, radiological (HRCT) and metabolic indices (FDG-PET-CT) of disease activity.

MATERIALS AND METHODS

This was a prospective observational study conducted between March 2007 and December 2008 at a tertiary care referral center in north India. Twenty-five symptomatic and histopathologically proven cases of sarcoidosis underwent FDG-PET-CT scanning at baseline and a follow-up scan in 21 patients at 6-9 months post-treatment with glucocorticoids.

RESULTS

FDG-PET-CT scan detected metabolic disease activity in 24 of the 25 patients with clinically active sarcoidosis. It also demonstrated many clinically inapparent sites of disease activity. Complete or partial metabolic response was seen in 17 of the 21 patients in whom a follow-up scan was available. Substantial degree of agreement was found between the metabolic response and the radiological response, whereas moderate agreement was found between clinical and metabolic responses.

CONCLUSIONS

FDG-PET-CT scanning is a useful imaging modality to assess disease activity, extent of disease involvement and response to treatment in clinically active sarcoidosis. There is substantial agreement between the HRCT and metabolic parameters of disease activity. Further, large sample size studies are proposed in order to identify the subset of patients who are likely to benefit the most from this sensitive modality of imaging, especially in developing countries where the cost of the procedure is an important concern.

Assessment of cardiac sarcoidosis with advanced imaging modalities

Sarcoidosis is a chronic systemic disease of unknown etiology that is characterized by the presence of noncaseating epithelioid granulomas, usually in multiple organs. Several studies have shown that sarcoidosis might be the result of an exaggerated granulomatous reaction after exposure to unidentified antigens in genetically susceptible individuals. Cardiac involvement may occur and lead to an adverse outcome: the heart mechanics will be affected and that causes ventricular failure, and the cardiac electrical system will be disrupted and lead to third degree atrioventricular block, malignant ventricular tachycardia, and sudden cardiac death. Thus, early diagnosis and treatment of this potentially devastating disease is critically important. However, sensitive and accurate imaging modalities have not been established. Recent studies have demonstrated the promising potential of cardiac magnetic resonance imaging (MRI) and (18)F-fluoro-2-deoxyglucose positron emission tomography ((18)F-FDG PET) in the diagnosis and assessment of cardiac sarcoidosis (CS). In this review, we discuss the epidemiology, etiology, histological findings, and clinical features of sarcoidosis. We also introduce advanced imaging including (18)F-FDG PET and cardiac MRI as more reliable diagnostic modalities for CS.

FDG PET imaging in sarcoidosis

The objective of this review is to highlight the clinical utility of FDG-PET/CT for evaluation of patients with chronic sarcoidosis. The emphasis was on the potential advantages and disadvantages of this technique in these patients based on which recommendations were made. The advantage of FDG-PET/CT technique is that it can visualize FDG accumulation in activated inflammatory cells and simultaneously provide PET and CT images. Of particular interest is the use of FDG-PET/CT for the staging and identification of occult sites and sites suitable for biopsy and for the assessment of inflammatory active sarcoidosis in patients with prolonged symptoms, especially when other markers of the disease are within normal values. FDG-PET/CT also provides a better visualization of extrathoracic sites of active sarcoidosis, such as in the bones, liver, spleen, and retroperitoneal lymph nodes. The use of FDG-PET/CT is of special interest in cardiac sarcoidosis because this potentially life-threatening disease is sometimes present in asymptomatic patients. FDG-PET/CT also has a role in the clinical management of patients with chronic persistent sarcoidosis, such as for planning treatment, monitoring response, and long-term follow-up. The limitations of FDG-PET/CT in patients with sarcoidosis are discussed in the context of a "sarcoidosis-lymphoma syndrome" and potentially excessive radiation exposure. Further prospective multicentre studies are needed to refine the clinical applications of FDG-PET/CT in patients with sarcoidosis and drive the field forward.

The role of 18F-FDG-PET and PET/CT in patients with sarcoidosis: an updated evidence-based review

RATIONALE AND OBJECTIVES

To provide an updated evidence-based review of the literature on the role of fluorine-18-fluorodeoxyglucose positron emission tomography (FDG-PET) or PET/computed tomography (PET/CT) in patients with sarcoidosis.

MATERIALS AND METHODS

A comprehensive literature search of PubMed/MEDLINE, Scopus, and Embase databases was conducted to find relevant published articles on FDG-PET or PET/CT in patients with sarcoidosis. Only those studies that satisfied all the following criteria were included: (1) FDG-PET or PET/CT performed in patients with histologically confirmed sarcoidosis, (2) sample size of at least 10 patients, and (3) whole-body PET studies performed. Information was collected concerning basic study, patient characteristics, and technical aspects. The main findings of the articles included have been described.

RESULTS

Reviewing titles and abstracts, 21 articles were selected. The role of FDG-PET or PET/CT was analyzed in assessing disease extent and activity and in treatment response evaluation. Comparison with other tracers had also been investigated. Recent studies evaluated the influence of these methods in the clinical management and their role as predictive tools in patients with sarcoidosis.

CONCLUSIONS

FDG-PET and PET/CT seem to be useful in staging, evaluating disease activity, and monitoring treatment response in patients with sarcoidosis. PET appears to have higher diagnostic accuracy compared to Gallium-67-citrate scintigraphy. Conversely, there is not enough evidence about the use of other PET tracers in patients with sarcoidosis. FDG-PET and PET/CT seem to have a role as predictive tools and may influence the clinical management in patients with sarcoidosis, but more studies are needed in this regard.

Advanced imaging of cardiac sarcoidosis

Sarcoidosis is a systemic granulomatous disease of unknown etiology. Cardiac involvement may occur, leading to an adverse outcome. Although early treatment to improve morbidity and mortality is desirable, sensitive and accurate detection of cardiac sarcoidosis remains a challenge. Accordingly, interest in the use of advanced imaging such as cardiac MR and PET with (18)F-FDG is increasing in order to refine the clinical workup. Although the field is still facing challenges and uncertainties, this article presents a summary of clinical background and the current state of diagnostic modalities and treatment of cardiac sarcoidosis.

[Update on the use of PET radiopharmaceuticals in inflammatory disease]

The use of molecular imaging with PET/CT technology using different radiotracers, especially the (18)F-FDG is currently spreading beyond the area of oncology, the most interest being placed on inflammatory and infectious diseases. This article presents a review of its contribution in different inflammatory conditions in the context of structural and conventional nuclear medicine imaging. Special emphasis is placed on the more significant diseases such as large-vessel vasculitis, sarcoidosis, rheumatoid arthritis and inflammatory bowel disease and the study of the atheroma plaque.