The role of 18F-FDG PET/CT for the diagnosis of infections in patients with hematological malignancies and persistent febrile neutropenia

What do we know About the Usefulness of 18F-FDG PET-CT for the Management of Invasive Fungal Infection? An International Survey

BACKGROUND

Recent data support 18F-FDG PET-CT for the management of infections in immunocompromised patients, including invasive fungal infection (IFI). However, its role is not well established in clinical practice. We performed an international survey to evaluate the knowledge of physicians about the usefulness of 18F-FDG PET-CT in IFI, in order to define areas of uncertainty.

METHODS

An online survey was distributed to infectious diseases working groups in December 2023-January 2024. It included questions regarding access to 18F-FDG PET-CT, knowledge on its usefulness for IFI and experience of the respondents. A descriptive analysis was performed.

RESULTS

180 respondents answered; 60.5% were Infectious Diseases specialists mainly from Spain (52.8%) and Italy (23.3%). 84.4% had access to 18F-FDG PET-CT at their own center. 85.6% considered that 18F-FDG PET-CT could be better than conventional tests for IFI. In the context of IFI risk, 81.1% would consider performing 18F-FDG PET-CT to study fever without a source and around 50% to evaluate silent lesions and 50% to assess response, including distinguishing residual from active lesions. Based on the results of the follow-up 18F-FDG PET-CT, 56.7% would adjust antifungal therapy duration. 60% would consider a change in the diagnostic or therapeutic strategy in case of increased uptake or new lesions. Uncovering occult lesions (52%) and diagnosing/excluding endocarditis (52.7%) were the situations in which 18F-FDG PET-CT was considered to have the most added value. There was a great variability in responses about timing, duration of uptake, the threshold for discontinuing treatment or the influence of immune status.

CONCLUSION

Although the majority considered that 18F-FDG PET-CT may be useful for IFI, many areas of uncertainty remain. There is a need for protocolized research to improve IFI management.

Usefulness of 18F-FDG PET-CT in the Management of Febrile Neutropenia: A Retrospective Cohort from a Tertiary University Hospital and a Systematic Review

Febrile neutropenia (FN) is a complication of hematologic malignancy therapy. An early diagnosis would allow optimization of antimicrobials. The 18F-FDG-PET-CT may be useful; however, its role is not well established. We analyzed retrospectively patients with hematological malignancies who underwent 18F-FDG-PET-CT as part of FN management in our university hospital and compared with conventional imaging. In addition, we performed a systematic review of the literature assessing the usefulness of 18F-FDG-PET-CT in FN. A total of 24 cases of FN underwent 18F-FDG-PET-CT. In addition, 92% had conventional CT. In 5/24 episodes (21%), the fever was of infectious etiology: two were bacterial, two were fungal, and one was parasitic. When compared with conventional imaging, 18F-FDG-PET-CT had an added value in 20 cases (83%): it diagnosed a new site of infection in 4 patients (17%), excluded infection in 16 (67%), and helped modify antimicrobials in 16 (67%). Antimicrobials could be discontinued in 10 (41.6%). We identified seven publications of low quality and one randomized trial. Our results support those of the literature. The available data suggest that 18F-FDG-PET-CT is useful in the management of FN, especially to diagnose fungal infections and rationalize antimicrobials. This review points out the low level of evidence and indicates the gaps in knowledge.

What Is New in Pulmonary Mucormycosis?

Mucormycosis is a rare but life-threatening fungal infection due to molds of the order Mucorales. The incidence has been increasing over recent decades. Worldwide, pulmonary mucormycosis (PM) presents in the lungs, which are the third main location for the infection after the rhino-orbito-cerebral (ROC) areas and the skin. The main risk factors for PM include hematological malignancies and solid organ transplantation, whereas ROC infections are classically favored by diabetes mellitus. The differences between the ROC and pulmonary locations are possibly explained by the activation of different mammalian receptors—GRP78 in nasal epithelial cells and integrin β1 in alveolar epithelial cells—in response to Mucorales. Alveolar macrophages and neutrophils play a key role in the host defense against Mucorales. The diagnosis of PM relies on CT scans, cultures, PCR tests, and histology. The reversed halo sign is an early, but very suggestive, sign of PM in neutropenic patients. Recently, the serum PCR test showed a very encouraging performance for the diagnosis and follow-up of mucormycosis. Liposomal amphotericin B is the drug of choice for first-line therapy, together with correction of underlying disease and surgery when feasible. After a stable or partial response, the step-down treatment includes oral isavuconazole or posaconazole delayed release tablets until a complete response is achieved. Secondary prophylaxis should be discussed when there is any risk of relapse, such as the persistence of neutropenia or the prolonged use of high-dose immunosuppressive therapy. Despite these novelties, the mortality rate from PM remains higher than 50%. Therefore, future research must define the place for combination therapy and adjunctive treatments, while the development of new treatments is necessary.

New approaches to management of fever and neutropenia in high-risk patients

PURPOSE OF REVIEW

Patients receiving treatment for acute leukaemia and haematopoietic cell transplantation (HCT) have prolonged neutropenia and are at high risk of neutropenic fever, with bacterial and particularly invasive fungal infections as feared complications, possessing potentially serious consequences including intensive care admission and mortality. Concerns for these serious complications often lead to long durations of broad-spectrum antimicrobial therapy and escalation to even broader therapy if fever persists. Further, the default approach is to continue neutropenic fever therapy until count recovery, leaving many patients who have long defervesced on prolonged antibiotics.

RECENT FINDINGS

This article details recent progress in this field with particular emphasis on early discontinuation studies in resolved neutropenic fever and improved imaging techniques for the investigation of those with persistent neutropenic fever. Recent randomized controlled trials have shown that early cessation of empiric neutropenic fever therapy is well tolerated in acute leukaemia and autologous HCT patients who are clinically stable and afebrile for 72 h. Delineation of the best approach to cessation (timing and/or use of fluoroquinolone prophylaxis) and whether this approach is well tolerated in the higher risk allogeneic HCT setting is still required. Recent RCT data demonstrate utility of FDG-PET/CT to guide management and rationalize antimicrobial therapy in high-risk patient groups with persistent neutropenic fever.

SUMMARY

Acute leukaemic and autologous HCT patients with resolved neutropenic fever prior to count recovery can have empiric therapy safely discontinued or de-escalated. There is an emerging role of FDG-PET/CT to support decision-making about antibiotic and antifungal use in high-risk persistent/recurrent neutropenic fever patients.

The role of 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (FDG PET/CT) in assessment of complex invasive fungal disease and opportunistic co-infections in patients with acute leukemia prior to allogeneic hematopoietic cell transplant

INTRODUCTION

Individuals diagnosed with acute lymphoid and myeloid malignancies are at significant risk of invasive fungal and bacterial infections secondary to their marked immunocompromised states with a significant high risk of mortality. The role of metabolic imaging with 18F-Fluorodeoxyglucose (FDG) Positron Emission Tomography/Computed Tomography (PET/CT) has been increasingly recognized in optimizing the diagnosis of invasive infection, monitoring the response to therapy and guiding the duration of antimicrobial therapy or need to escalate to surgical intervention.

METHODS

Two distinct cases of pulmonary co-infection of rare fungal and bacterial pathogens are explored in severely immunocompromised individuals where FDG PET/CT aided both patients to make a full recovery and transition to HCT. The first case explores mixed Scedosporium apiospermum and Rhizomucor pulmonary infection on a background of T cell/myeloid mixed phenotype acute leukemia ultimately warranting long-term antifungal therapy and lobectomy prior to HCT. The second case explores Fusarium and Nocardia pulmonary infection on a background of relapsed AML also warranting surgical resection with lobectomy and long-term antimicrobials prior to transition to HCT.

DISCUSSION

The cases highlight the utility of FDG PET/CT to support the diagnosis of infections, including the presence or absence of disseminated infection, and to provide highly sensitive monitoring of the infection over time. FDG PET/CT played a key role in directing therapy duration decisions and prompted the necessity for surgical intervention. Ultimately, the use of FDG PET/CT allowed for a successful transition to HCT highlighting its value in this clinical setting.

CONCLUSION

FDG PET/CT has an emerging role in the diagnostic and monitoring pathway for complex infections in high-risk immunocompromised patients.

FDG-PET/CT in Fever of Unknown Origin, Bacteremia, and Febrile Neutropenia

Fever of unknown origin, bacteremia, and febrile neutropenia are diagnostic challenges. FDG-PET/CT is a well-established modality in infection imaging and the literature increasingly supports its use in these settings. In fever of unknown origin, FDG-PET/CT is helpful, but diagnostic yield depends on patient selection and inflammatory markers. In bacteremia, FDG-PET/CT is cost-effective, reduces morbidity and mortality, and impacts treatment strategy. Although use of FDG-PET/CT in these domains is not established as part of a definitive diagnostic strategy, FDG-PET/CT may help establish final diagnosis in a difficult population and should be considered early in the diagnostic process.

Diagnostic work up to assess early response indicators in invasive pulmonary aspergillosis in adult patients with haematologic malignancies

In immunocompromised patients with acute leukaemia as well as in allogeneic hematopoietic stem cell transplant patients, pulmonary lesions are commonly seen. Existing guidelines provide useful algorithms for diagnostic procedures and treatment options, but they do not give recommendations on how to evaluate early success or failure and if or when it is best to change therapy. Here, we review the diagnostic techniques currently used in association with clinical findings and propose an approach using a combination of computer tomography, clinical and all available biomarkers and inflammation parameters, especially those positive at baseline, to assess early response in invasive pulmonary aspergillosis. Computed tomography scans should be carried out at regular intervals during early and long-term follow-up. Imaging on day seven, or even earlier in clinically unstable patients, combined with an additional testing of biomarkers and inflammatory markers in between, is needed for a reliable assessment at day 14. If no improvement is seen after 2 weeks of therapy or the clinical condition is deteriorating, a change of antifungal therapy should be considered. Alleged breakthrough infections or treatment failure should undergo early diagnostic workup, including tissue biopsies when possible, to retrieve fungal cultures for resistance testing.

FDG-PET/CT in managing infection in patients with hematological malignancy: clinician knowledge and experience in Australia

PET/CT is useful for investigation of neutropenic fever (NF) and potential invasive fungal infection (IFI) in those with hematological malignancies (HM). An online survey evaluating the utility and current practices regarding PET/CT scanning for investigation of NF was distributed to infectious diseases (ID) clinicians and hematologists via email lists hosted by key professional bodies. One-hundred and forty-five clinicians responded (120 ID; 25 hematologists). Access to PET/CT was fair but timeliness of investigation was limited (within 3 days in 35% and 46% of ID and hematology respondents, respectively). Among those with experience with PET/CT for infection (n = 109), 40% had utilized PET/CT for prolonged NF and 20% for diagnosing IFI. The majority of respondents indicated the desire to utilize PET/CT more frequently for infection indications. There is a strong desire among surveyed Australian clinicians to use PET/CT for prolonged NF and potential IFI. However, access to PET/CT is a current barrier to uptake.

Why are so many cases of invasive aspergillosis missed?

Invasive aspergillosis (IA) incidence is increasing in several countries like France, and numerous cases are indeed missed and still only diagnosed at autopsy as evidenced by recently published data. Such missed diagnoses are obviously encountered when appropriate diagnostic tools are not available especially in low resource areas or when biologists have not been trained enough in medical mycology (i.e., microscopic examination and culture in most of those areas). Besides logistical issues, which are indeed critical, IA may not be recognized because clinicians failed to consider that risk factors are evolving with the IA burden now observed among patients with chronic lymphoid malignancies or receiving new biotherapies, with diabetes mellitus or liver cirrhosis and/or acute alcoholic hepatitis, with patients from the intensive care unit (ICU) and among patients with some predisposing primary immune deficiencies now reaching the adult's age. This is also the case for human immunodeficiency virus (HIV)-infected patients who failed to meet the classical definitions of IA. From the radiology perspective, new entities of IA have also emerged which absolutely need to be recognized especially bronchial-based-IA among allogeneic stem cell transplant recipients. Finally, from the laboratory side, contribution and limits of indirect blood biomarkers should be integrated to the clinical life in order not to miss IA cases. To conclude, several diagnostic tools should be combined and a constant dialog between laboratory and clinics is crucial to appropriately diagnose IA.

Clinical value of FDG-PET/CT in bacteremia of unknown origin with catalase-negative gram-positive cocci or Staphylococcus aureus

INTRODUCTION

Bacteremia is associated with high mortality, especially when the site of infection is unknown. While conventional imaging usually focus on specific body parts, FDG-PET/CT visualizes hypermetabolic foci throughout the body.

PURPOSE

To investigate the ability of FDG/PET-CT to detect the site of infection and its clinical impact in bacteremia of unknown origin with catalase-negative Gram-positive cocci (excluding pneumococci and enterococci) or Staphylococcus aureus (BUOCSA).

METHODS

We retrospectively identified 157 patients with 165 episodes of BUOCSA, who subsequently underwent FDG-PET/CT. Data were collected from medical records. Decision regarding important sites of infection in patients with bacteremia was based on the entire patient course and served as reference diagnosis for comparison with FDG-PET/CT findings. FDG-PET/CT was considered to have high clinical impact if it correctly revealed site(s) of infection in areas not assessed by other imaging modalities or if other imaging modalities were negative/equivocal in these areas, or if it established a new clinically relevant diagnosis, and/or led to change in antimicrobial treatment.

RESULTS

FDG-PET/CT detected sites of infection in 56.4% of cases and had high clinical impact in 47.3%. It was the first imaging modality to identify sites of infection in 41.1% bacteremia cases, led to change of antimicrobial therapy in 14.7%, and established a new diagnosis unrelated to bacteremia in 9.8%. Detection rate and clinical impact were not significantly influenced by duration of antimicrobial treatment preceding FDG-PET/CT, days from suspicion of bacteremia to FDG-PET/CT-scan, type of bacteremia, or cancer.

CONCLUSION

FDG-PET/CT appears clinically useful in BUOCSA. Prospective studies are warranted for confirmation.

FDG PET/CT imaging in detecting and guiding management of invasive fungal infections: a retrospective comparison to conventional CT imaging

PURPOSE

Invasive fungal infections (IFIs) are common in immunocompromised patients. While early diagnosis can reduce otherwise high morbidity and mortality, conventional CT has suboptimal sensitivity and specificity. Small studies have suggested that the use of FDG PET/CT may improve the ability to detect IFI. The objective of this study was to describe the proven and probable IFIs detected on FDG PET/CT at our centre and compare the performance with that of CT for localization of infection, dissemination and response to therapy.

METHODS

FDG PET/CT reports for adults investigated at Peter MacCallum Cancer Centre were searched using keywords suggestive of fungal infection. Chart review was performed to describe the risk factors, type and location of IFIs, indication for FDG PET/CT, and comparison with CT for the detection of infection, and its dissemination and response to treatment.

RESULTS

Between 2007 and 2017, 45 patients had 48 proven/probable IFIs diagnosed prior to or following FDG PET/CT. Overall 96% had a known malignancy with 78% being haematological. FDG PET/CT located clinically occult infection or dissemination to another organ in 40% and 38% of IFI patients, respectively. Of 40 patients who had both FDG PET/CT and CT, sites of IFI dissemination were detected in 35% and 5%, respectively (p < 0.001). Of 18 patents who had both FDG PET/CT and CT follow-up imaging, there were discordant findings between the two imaging modalities in 11 (61%), in whom normalization of FDG avidity of a lesion suggested resolution of active infection despite a residual lesion on CT.

CONCLUSION

FDG PET/CT was able to localize clinically occult infection and dissemination and was particularly helpful in demonstrating response to antifungal therapy.

What, where and why: exploring fluorodeoxyglucose-PET's ability to localise and differentiate infection from cancer

PURPOSE OF REVIEW

To review the utility of FDG-PET imaging in detecting the cause of fever and infection in patients with cancer.

RECENT FINDINGS

FDG-PET has been shown to have high sensitivity and accuracy for causes of neutropenic fever, leading to higher diagnostic certainty in this group. Recent advances in pathogen-specific labelling in PET to identify Aspergillus spp. and Yersinia spp. infections in mice, as well as differentiating between Gram-positive, Gram-negative and mycobacterial infections are promising.

SUMMARY

Patients with cancer are vulnerable to infection and fever, and the causes of these are frequently unclear using conventional diagnostic methods leading to high morbidity and mortality, length of stay and costs of care. FDG-PET/CT, with its unique complementary functional and anatomical information as well as its whole-body imaging capability, has demonstrated use in detecting occult infection in immunocompromised patients, including invasive fungal and occult bacterial infections, as well as defining extent of infection. By demonstrating disease resolution following treatment and allowing earlier cessation of therapy, FDG-PET acts as a key tool for antimicrobial and antifungal stewardship. Limitations include at times poor differentiation between infection, malignancy and sterile inflammation, however, exciting new technologies specific to infectious pathogens may help alleviate that issue. Further prospective randomised research is needed to explore these benefits in a nonbiased fashion.

Diagnosis and empirical treatment of fever of unknown origin (FUO) in adult neutropenic patients: guidelines of the Infectious Diseases Working Party (AGIHO) of the German Society of Hematology and Medical Oncology (DGHO)

Fever may be the only clinical symptom at the onset of infection in neutropenic cancer patients undergoing myelosuppressive chemotherapy. A prompt and evidence-based diagnostic and therapeutic approach is mandatory. A systematic search of current literature was conducted, including only full papers and excluding allogeneic hematopoietic stem cell transplant recipients. Recommendations for diagnosis and therapy were developed by an expert panel and approved after plenary discussion by the AGIHO. Randomized clinical trials were mainly available for therapeutic decisions, and new diagnostic procedures have been introduced into clinical practice in the past decade. Stratification into a high-risk versus low-risk patient population is recommended. In high-risk patients, initial empirical antimicrobial therapy should be active against pathogens most commonly involved in microbiologically documented and most threatening infections, including Pseudomonas aeruginosa, but excluding coagulase-negative staphylococci. In patients whose expected duration of neutropenia is more than 7 days and who do not respond to first-line antibacterial treatment, specifically in the absence of mold-active antifungal prophylaxis, further therapy should be directed also against fungi, in particular Aspergillus species. With regard to antimicrobial stewardship, treatment duration after defervescence in persistently neutropenic patients must be critically reconsidered and the choice of anti-infective agents adjusted to local epidemiology. This guideline updates recommendations for diagnosis and empirical therapy of fever of unknown origin in adult neutropenic cancer patients in light of the challenges of antimicrobial stewardship.

Invasive mould infections in the ICU setting: complexities and solutions

Infections caused by filamentous fungi represent a major burden in the ICU. Invasive aspergillosis is emerging in non-neutropenic individuals with predisposing conditions, e.g. corticosteroid treatment, chronic obstructive pulmonary disease, liver cirrhosis, solid organ cancer, HIV infection and transplantation. Diagnosis is challenging because the signs and symptoms are non-specific, and initiation of additional diagnostic examinations is often delayed because clinical suspicion is low. Isolation of an Aspergillus species from the respiratory tract in critically ill patients, and tests such as serum galactomannan, bronchoalveolar lavage 1-3-β-d-glucan and specific PCR should be interpreted with caution. ICU patients should start adequate antifungal therapy upon suspicion of invasive aspergillosis, without awaiting definitive proof. Voriconazole, and now isavuconazole, are the drugs of choice. Mucormycosis is a rare, but increasingly prevalent disease that occurs mainly in patients with uncontrolled diabetes mellitus, immunocompromised individuals or previously healthy patients with open wounds contaminated with Mucorales. A high proportion of cases are diagnosed in the ICU. Rapidly progressing necrotizing lesions in the rhino-sinusal area, the lungs or skin and soft tissues are the characteristic presentation. Confirmation of diagnosis is based on demonstration of tissue invasion by non-septate hyphae, and by new promising molecular techniques. Control of underlying predisposing conditions, rapid surgical resection and administration of liposomal amphotericin B are the main therapeutic actions, but new agents such as isavuconazole are a promising alternative. Patients with mucormycosis receive a substantial part of their care in ICUs and, despite advances in diagnosis and treatment, mortality remains very high.

[18F]FDG-PET/CT for the diagnosis of patients with fever of unknown origin

BACKGROUND AND AIMS

The diagnosis of patients with fever of unknown origin (FUO) remains a challenging medical problem. We aimed to assess the diagnostic contribution of 18-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET)/computed tomography (CT) for the evaluation of FUO.

METHODS

We performed a 4-year retrospective single-center study of all hospitalized patients that underwent FDG-PET/CT for evaluation of FUO. The final diagnosis of the febrile disease was based on clinical, microbiological, radiological and pathological data available at the final follow-up. Predictors for a contributory exam were sought.

RESULTS

One hundred and twelve patients underwent FDG-PET/CT for the investigation of FUO in the years 2008-2012 and were included in the study. A final diagnosis was determined in 83 patients (74%) and included: infectious disease in 49 patients (43%), non-infectious inflammatory disease in 17 patients (16%), malignancies in 15 patients (14%), other diagnoses in 2 patients (1.7%), FUO resolved with no diagnosis and no evidence of disease during a 6-month follow-up in 23 patients (20%), and death with fever and with no diagnosis in 6 patients (5%). Seventy-four FDG-PET/CT studies (66%) were considered clinically helpful and contributory to diagnosis (46% positive contributory value and 20.5% contributory to exclusion of diagnosis). PET/CT had a sensitivity of 72.2%, a specificity of 57.5%, a positive predictive value (PPV) of 74.2% and a negative predictive value (NPV) of 53.5%. On multivariable analysis, significant predictors of a positive PET/CT contributory to diagnosis were a short duration of fever and male gender.

CONCLUSIONS

PET/CT is an important diagnostic tool for patients with FUO.