Detection of underlying malignancy in patients with paraneoplastic neurological syndromes: comparison of 18F-FDG PET/CT and contrast-enhanced CT

Clinical approach to diagnosis of paraneoplastic neurologic syndromes

The correct diagnosis of a paraneoplastic neurologic syndrome (PNS) first requires the identification of the syndrome as one of those defined as high-risk (previously called classical) or intermediate-risk for cancer in the 2021 PNS diagnostic criteria. Testing for neuronal antibodies should be restricted to these syndromes as indiscriminate request decreases the diagnostic value of the antibodies. Identifying onconeural (high-risk for cancer) or intermediate-risk for cancer antibodies supports the paraneoplastic diagnosis and mandates the search for an underlying cancer. Tumor screening must follow the published guidelines. Repeated screening is indicated in neurologic syndromes with onconeural antibodies and patients with high-risk for cancer neurologic syndromes unless they present neuronal antibodies which are not associated with cancer. Neuronal antibodies should be screened by immunohistochemistry and confirmed by immunoblot (intracellular antigens) or cell-based assay (CBA) (surface antigens). Positive results only by immunoblot or CBA should be taken with caution. Although the 2021 diagnostic criteria for PNS do not capture all PNS, as they do not allow to diagnose definite PNS neurologic syndromes without neuronal antibodies, the updated criteria represent a step forward to differentiate true PNS from neurologic syndromes that coincide in time with cancer diagnosis without having a pathogenic link.

Whole-body computed tomography as first-line imaging procedure to exclude cancer in patients with neurological suspicion of paraneoplastic syndromes: shall clinical practice adhere to recommendations?

INTRODUCTION

To assess the efficacy of whole-body computed tomography (WB-CT) as imaging procedure to exclude cancer in patients with neurological symptoms and signs at clinical onset.

METHODS

A retrospective observational study was designed to identify consecutive WB-CT requested by the Neurology Unit with a suspicion of an underlying tumor potentially linked to a paraneoplastic neurological syndrome (PNS) between January 2019 and February 2022. The following data were collected: diagnosis at admission and at discharge, the presence of onconeural antibodies, the scans dose length product (DLP), the estimated effective dose (ED), the total estimated time requested; the PNS-Care-Score was retrospectively calculated only in subjects with available antibodies.

RESULTS

The total number of patients included was 158. In 13/158 (positive group) a malignant or locally aggressive neoplasm was found while in 145/158 no malignant lesions were found on the WB-CT. Among the positive group, in 7/13 onconeural antibodies were diagnosed, resulting negative in all cases and the most frequent tumor was lung cancer (30.8%). PNS-Care-Score was of 6-7 in 2/7 (probable PNS) and in no case the PNS-Care-Score was ≥8 (definite PNS). The mean DLP for all the scans was 2798 ± 952 mGy cm (average estimated ED of 42 ± 14 mSv). The total estimated time requested for all scans was 11,060 min.

CONCLUSION

If a PNS is suspected, we encourage the prescription of unenhanced chest CT and/or abdomen/testis/female pelvis ultrasound and/or mammography based on clinical picture. The WB-CT using a single portal phase would be appropriate as a second-line technique while magnetic resonance imaging might be indicated for the exclusion of nervous system diseases.

IMPLICATIONS FOR PRACTICE

Our suggestion results in saving in terms of radiation exposure, financial resources and time.

18F-fluorodeoxyglucose positron emission tomography/ computed tomography in the diagnosis of suspected paraneoplastic syndromes: A retrospective analysis

Paraneoplastic syndromes are a rare clinical presentation of tumor thought to affect 0.01% of patients with cancer. Paraneoplastic syndromes present a diagnostic challenge as a wide variety of signs and symptoms may appear. This study examines the use of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) as a diagnostic imaging tool for detecting tumor in suspected paraneoplastic syndrome cases. This single-center retrospective study included patients with suspected paraneoplastic syndrome who underwent whole-body ¹⁸F-FDG PET/CT scan between December 2005 and December 2016. Associated clinical data were gathered via electronic chart review. Patient records were reviewed for age, sex, clinical signs and symptoms, ancillary diagnostic procedures, date of diagnosis, and follow-up time. Ninety-nine patients met inclusion criteria for this study. Mean follow-up period was 1.8 years. Cancer prevalence was 12.1%. The ¹⁸F-FDG PET/CT results are as follows: 10 true positives, 5 false positives, 82 true negatives, and 2 false negatives. The diagnostic values are as follows: sensitivity 83.3%, specificity 94.3%, positive predictive value 66.7%, and negative predictive value (NPV) 97.6%. The high NPV in our study supports the effectiveness of ¹⁸F-FDG PET/CT to rule out tumor in suspected paraneoplastic syndrome. Future research aims to analyze which patients with suspected paraneoplastic syndrome would benefit most from ¹⁸F-FDG PET/CT.

Imaging Workup of Suspected Classical Paraneoplastic Neurological Syndromes: A Systematic Review and Retrospective Analysis of 18F-FDG-PET-CT

RATIONALE AND OBJECTIVES

This study aimed to assess the clinical efficacy of positron emission tomography (PET) or combined PET-computed tomography (CT) with ¹⁸F-fluorodeoxyglucose (FDG) for whole-body cancer screening in patients with suspected paraneoplastic neurological syndromes (PNS). The following main research questions were addressed: What is the percentage of positive findings to be expected in whole-body FDG-PET-CT in adult patients with PNS? How many false positives can be expected as assessed by clinical and histopathological workup? Are there patients who present with a tumor despite initially negative findings?

MATERIALS AND METHODS

This is a systematic review of the literature and retrospective analysis of FDG-PET-CT and clinical follow-up data from 45 consecutive patients (age: 56.6 ± standard deviation 15.8 years, 14 female, 31 male). Suspicious lesions were identified and correlated with immediate workup and clinical follow-up.

RESULTS

Fourteen studies were included in the review. Eleven malignancies (24.4% of patients) were identified by FDG-PET-CT in this sample. This is a higher percentage of positive findings compared to most previous reports. There was one initially negative finding.

CONCLUSIONS

Whole-body FDG-PET-CT is suitable to identify additional malignancies in patients with suspected classical PNS referred to a tertiary medical center. The utility by means of true-positive findings is higher in classical PNS than suggested by studies in less select patient populations.

The Utility of FDG-PET/CT in Clinically Suspected Paraneoplastic Neurological Syndrome: A Literature Review and Retrospective Case Series

Paraneoplastic neurological syndrome (PNS) describes a spectrum of rare, heterogeneous neurological conditions associated with an underlying malignancy. Diagnosis of PNS is inherently difficult, with frequent misdiagnosis and delay. The literature suggests an underlying immune-mediated pathophysiology, and patients are usually tested for the presence of onconeural antibodies. With direct tumor therapy being the most effective method of stabilizing patients, there is a strong emphasis on detecting underlying tumors. The sensitivity of conventional CT imaging is often inadequate in such patients. While FDG-PET imaging has already been shown to be effective at detecting these tumors, FDG-PET/CT, combining both structural and functional imaging in a single study, is a more recent technique. To study the utility of FDG-PET/CT, we conducted a systematic literature review and a retrospective study. We identified 41 patients who underwent imaging for clinically suspected PNS at the regional PET-CT and neurosciences center based at the Royal Preston Hospital between 2007 and 2014 and compared the results to conventional investigations. Five patients had FDG-PET/CT tracer avidity suspicious of malignant disease, and four of these were subsequently diagnosed with cancer. Sensitivity and specificity were calculated to be 100 and 97.3%, respectively, with positive predictive value 80% and negative predictive value 100%. This compares to a sensitivity and specificity of 50 and 100%, respectively, for CT and 50 and 89%, respectively, for onconeural antibodies. These findings are in line with previous studies and support the diagnostic accuracy of FDG-PET/CT for the detection of underlying malignancy.

Diagnostic Value of Positron Emission Tomography Combined with Computed Tomography for Evaluating Critically Ill Neurological Patients

Purpose

¹⁸F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) is a promising new tool for the identification of inflammatory, infectious, and neoplastic foci. The aim of our work was to evaluate the diagnostic value of FDG-PET/CT in patients treated on a neurological/neurosurgical ICU or stroke unit.

Methods

We performed a single-center, 10-year, retrospective evaluation of the value of FDG-PET/CT in critically ill adult patients with severe neurological disease.

Results

42 patients underwent FDG-PET/CT. Of these, 15 were ventilated and 10 were under vasopressor support. We identified four indications for performing FDG-PET/CT: (1) excluding a paraneoplastic etiology in an otherwise unexplained encephalitis, encephalopathy or neuropathy, (2) detecting a large-vessel vasculitis in patients with ischemic stroke, (3) detecting an infectious focus in sepsis, and less frequently (4) evaluating cerebral metabolism. In 22 patients who were evaluated for an unknown malignancy, 5 scans revealed either a previously unknown tumor or unknown metastases of a previously treated malignancy. Of 11 patients investigated for large-vessel vasculitis, 2 showed an inflammation of arteries supplying the brain. Of six sepsis cases, FDG-PET/CT identified an infectious focus in four.

Summary

We found FDG-PET/CT to be a helpful tool in critically ill neurological patients. The results of the FDG-PET/CT had direct therapeutic consequences in the 12 true-positive cases. In 24 of the 29 negative cases, FDG-PET/CT helped exclude alternative diagnoses and/or influenced therapy. Our findings demonstrate the feasibility and diagnostic benefit of FDG-PET/CT in this group of patients.

Whole-Body 18F-FDG PET and 18F-FDG PET/CT in Patients with Suspected Paraneoplastic Syndrome: A Systematic Review and Meta-Analysis of Diagnostic Accuracy

The purpose of this study was to assess the diagnostic performance of whole-body ¹⁸F-FDG PET or ¹⁸F-FDG PET/CT for detection of underlying malignancy in patients with clinically suspected neurologic and nonneurologic paraneoplastic syndromes. Methods: A systematic search was performed in PubMed (Medline), Embase, and Scopus (last updated November 2016) to identify relevant published studies reporting the performance of ¹⁸F-FDG PET or ¹⁸F-FDG PET/CT in patients with suspected paraneoplastic syndrome. Histopathologic confirmation or clinical follow-up was considered as the reference standard. Pooled estimates, with 95% confidence intervals (CIs), of sensitivity, specificity, and diagnostic odds ratio were calculated. A summary receiver-operating-characteristic curve was constructed, and the area under the curve (AUC) was determined along with the Q* index. Results: Twenty-one studies including a total of 1,293 individual patients suspected of having a paraneoplastic syndrome and who underwent ¹⁸F-FDG PET or ¹⁸F-FDG PET/CT examinations met our inclusion criteria. There was moderate to high heterogeneity among the included studies. The pooled sensitivity, specificity, and diagnostic odds ratio of ¹⁸F-FDG PET or ¹⁸F-FDG PET/CT for the detection of underlying malignancy were 0.81 (95% CI, 0.76-0.86), 0.88 (95% CI, 0.86-0.90), and 34.03 (95% CI, 18.76-61.72), respectively. The AUC and the Q* index were 0.916 (SE, 0.018) and 0.849, indicating excellent diagnostic accuracy. The diagnostic accuracy was slightly improved after studies with high applicability concerns were excluded (AUC, 0.931; SE, 0.020). In a subgroup analysis, ¹⁸F-FDG PET/CT was found to have a significantly higher specificity (0.89 vs. 0.79) than ¹⁸F-FDG PET alone, with no evidence of significant difference in the overall performance (AUC, 0.930 vs. 0.891; 2-tailed P value for difference, 0.31). Conclusion: This meta-analysis of available studies demonstrates that whole-body ¹⁸F-FDG PET or ¹⁸F-FDG PET/CT has high diagnostic accuracy and moderate to high sensitivity and specificity for detection of underlying malignancy in patients suspected of having a paraneoplastic syndrome.

Limbic Encephalitis Diagnosed With 18F-FDG PET/CT

Limbic encephalitis is a subacute onset syndrome characterized by short-term memory impairment, confusion, temporal lobe epilepsy, hypothalamic dysfunction, and psychiatric symptoms. Common causes are autoimmune disorders or idiopathic disease, although it has been associated to tumors. We report the case of a woman arrived at the emergency department having had fluctuating impaired memory for 2 weeks. The first MRI was normal. It was decided to perform lumbar puncture and PET/CT to exclude viral origin or paraneoplastic syndrome. Typical abnormalities were found in the second MRI (1 month after previous); however, FDG PET is a useful tool that contributes to early detection.

Impact on Patient Management of [18F]-Fluorodeoxyglucose-Positron Emission Tomography (PET) Used for Cancer Diagnosis: Analysis of Data From the National Oncologic PET Registry

INTRODUCTION

We assessed the impact of [(18)F]-fluorodeoxyglucose (FDG)-positron emission tomography (PET) on intended management of patients in the National Oncologic PET Registry (NOPR) for three different diagnostic indications: (a) determining whether a suspicious lesion is cancer (Dx), (b) detecting an unknown primary tumor site when there is confirmed or strongly suspected metastatic disease (cancer of unknown primary origin [CUP]), and (c) detecting a primary tumor site when there is a presumed paraneoplastic syndrome (PNS).

METHODS

We reviewed a sample of randomly selected reports of NOPR subjects who underwent PET for Dx and CUP and all reports for PNS to find subjects for analysis. For these studies, we evaluated the impact of PET on referring physicians' intended management, based on their management plans reported before and after PET.

RESULTS

Intended management was changed more frequently in the CUP group (43.1%) than in the Dx (23.9%) and PNS (25.4%) groups (CUP vs. Dx, p < .0001; PNS vs. Dx, p < .0001; CUP vs. PNS, p < .0002). Referring physicians reported that, in light of PET results, they were able to avoid further testing in approximately three-fourths of patients (71.8%-74.6%). At the time when the post-PET forms were completed, biopsies of suspicious sites had been performed in 21.2%, 32.4%, and 23.2%, respectively, of Dx, CUP, and PNS cases.

CONCLUSION

Our analysis of NOPR data shows that PET appears to have a substantial impact on intended management when used for three common diagnostic indications.

IMPLICATIONS FOR PRACTICE

[(18)F]-fluorodeoxyglucose-positron emission tomography appears to have a substantial impact on intended management when used for three targeted diagnostic indications: (a) determining whether a suspicious lesion is cancer, (b) detecting an unknown primary tumor site in a patient with confirmed or strongly suspected metastatic disease, and (c) detecting a primary tumor site in a patient with a presumed paraneoplastic syndrome.

Accuracy of FDG-PET/CT and paraneoplastic antibodies in diagnosing cancer in paraneoplastic neurological syndromes

OBJECTIVE

There is still no consensus about whether to perform PET/CT to detect carcinoma in paraneoplastic neurological syndromes (PNS) in patients with or without antibodies. The aim of this study is to determine the diagnostic accuracy of PET/CT and antibodies in patients with PNS.

MATERIAL AND METHODS

A retrospective study was conducted on patients with clinically suspected PNS between 2008 and 2013. The association between histopathological findings, paraneoplastic antibodies, and PET/CT findings were evaluated. Sensitivity and specificity for the detection of underlying malignancy were calculated for PET/CT and paraneoplastic antibodies.

RESULTS

A total of 42 patients were analyzed. Of these 42 patients, 32 (75%) had a classical PNS, 6 (14%) had positive PET/CT findings, and 34 were tested for the presence of antibodies (anti-Hu Ab, anti-Yo Ab, and anti-Ri Ab). Twenty one of 34 patients had positive antibodies. Of the 6 patients with positive PET/CT findings, 6 had positive histopathological results. Among 21 patients with positive biomarkers, carcinoma was confirmed only in 5 patients. One patient with negative antibodies, but positive PET/CT findings, was diagnosed with a tumor. Gastric carcinoma was detected in 1 patient with negative PET/CT findings and antibodies during follow-up. Based on the results, PET/CT was found to have 85.71% sensitivity, 100% specificity, 100% positive and 97.22% negative predictive values in the detection of tumors.

CONCLUSION

PET/CT has a certain diagnostic accuracy for detecting underlying malignancy in patients with PNS, regardless of the presence of paraneoplastic antibodies.

[Radiological diagnostics in CUP syndrome]

CLINICAL/METHODICAL ISSUE

Imaging plays an essential role in the therapeutic management of cancer of unknown primary (CUP) patients for localizing the primary tumor, for the identification of tumor entities for which a dedicated therapy regimen is available and for the characterization of clinicopathological subentities that direct the subsequent diagnostic and therapeutic strategy.

STANDARD RADIOLOGICAL METHODS

Modalities include conventional x-ray, computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound as well as positron emission tomography (PET)-CT and MRI-PET.

PERFORMANCE

In whole body imaging CT has a high sensitivity for tumor entities which frequently present as a metastasized cancer illness. According to the current literature CT is diagnostic in 86% of patients with pancreatic carcinoma, in 36% of patients with colon carcinoma and in 74% of patients with lung carcinoma. Additionally a meta-analysis showed that for patients with squamous cell carcinoma and cervical lymph node metastases a positive diagnosis was possible in 22% of the cases using CT, in 36% using MRI and in 28-57% using 18F-fluorodeoxyglucose PET-CT ((18)F-FDG PET-CT). In addition, MRI plays an important role in the localization of primary occult tumors (e.g. breast and prostate) because of its high soft tissue contrast and options for functional imaging.

ACHIEVEMENTS

At the beginning of the diagnostic algorithm stands the search for a possible primary tumor and CT of the neck, thorax and abdomen is most frequently used for whole body staging. Subsequent organ-specific imaging examinations follow, e.g. mammography in women with axillary lymphadenopathy. For histological and immunohistochemical characterization of tumor tissue, imaging is also applied to identify the most accessible and representative tumor manifestation for biopsy. Tumor biopsy may be guided by CT, MRI or ultrasound and MRI also plays a central role in the localization of primary occult tumors because of superior soft tissue contrast and options for functional imaging (perfusion, diffusion), e.g. investigation of breast carcinoma or prostate carcinoma.

PRACTICAL RECOMMENDATIONS

Whole body staging stands at the beginning of the diagnostic algorithm in CUP syndrome to localize a potential primary tumor. Clinically, contrast-enhanced CT of the neck, thorax and abdomen is frequently applied; however, many studies have demonstrated augmented sensitivity of (18)F-FDG PET-CT for the detection of primary tumors and metastatic tumor manifestations.

The pivotal role of FDG-PET/CT in modern medicine

The technology behind positron emission tomography (PET) and the most widely used tracer, 2-deoxy-2-[18F]fluoro-D-glucose (FDG), were both conceived in the 1970s, but the latest decade has witnessed a rapid emergence of FDG-PET as an effective imaging technique. This is not least due to the emergence of hybrid scanners combining PET with computed tomography (PET/CT). Molecular imaging has enormous potential for advancing biological research and patient care, and FDG-PET/CT is currently the most widely used technology in this domain. In this review, we discuss contemporary applications of FDG-PET and FDG-PET/CT as well as novel developments in quantification and potential future indications including the emerging new modality PET/magnetic resonance imaging.