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

Canadian Consensus Guidelines for the Diagnosis and Treatment of Autoimmune Encephalitis in Adults

Autoimmune encephalitis is increasingly recognized as a neurologic cause of acute mental status changes with similar prevalence to infectious encephalitis. Despite rising awareness, approaches to diagnosis remain inconsistent and evidence for optimal treatment is limited. The following Canadian guidelines represent a consensus and evidence (where available) based approach to both the diagnosis and treatment of adult patients with autoimmune encephalitis. The guidelines were developed using a modified RAND process and included input from specialists in autoimmune neurology, neuropsychiatry and infectious diseases. These guidelines are targeted at front line clinicians and were created to provide a pragmatic and practical approach to managing such patients in the acute setting.

Paraneoplastic Syndromes from Head to Toe: Pathophysiology, Imaging Features, and Workup

Patients often have symptoms due to the mass effect of a neoplasm on surrounding tissues or the development of distant metastases. However, some patients may present with clinical symptoms that are not attributable to direct tumor invasion. In particular, certain tumors may release substances such as hormones or cytokines or trigger an immune cross-reactivity between malignant and normal body cells, resulting in characteristic clinical features that are broadly referred to as paraneoplastic syndromes (PNSs). Recent advances in medicine have improved the understanding of the pathogenesis of PNSs and enhanced their diagnosis and treatment. It is estimated that 8% of patients with cancer develop a PNS. Diverse organ systems may be involved, most notably the neurologic, musculoskeletal, endocrinologic, dermatologic, gastrointestinal, and cardiovascular systems. Knowledge of various PNSs is necessary, as these syndromes may precede tumor development, complicate the patient's clinical presentation, indicate tumor prognosis, or be mistaken for metastatic spread. Radiologists should be familiar with the clinical presentations of common PNSs and the selection of appropriate imaging examinations. Many of these PNSs have imaging features that can assist with arriving at the correct diagnosis. Therefore, the key radiographic findings associated with these PNSs and the diagnostic pitfalls that can be encountered during imaging are important, as their detection can facilitate early identification of the underlying tumor, reveal early recurrence, and enable monitoring of the patient's response to therapy. ^© RSNA, 2023 Quiz questions for this article are available in the supplemental material.

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.

The role of [18F]FDG PET/CT in paraneoplastic autoimmune disorders: an umbrella review

Paraneoplastic autoimmune disorders (PAD) are a group of autoimmune diseases associated with neoplasms. Several evidence-based articles (systematic reviews and meta-analyses) have reported data about the role of positron emission tomography (PET) and related hybrid modalities (e.g., PET/CT) using 2-deoxy-2-[18F]fluoro-D-glucose ([¹⁸F]FDG) in patients with PAD. We performed an umbrella review of published systematic reviews and meta-analyses in this setting to provide an evidence-based summary and suggestions for further studies. Several databases were searched to find systematic reviews and meta-analysis on [¹⁸F]FDG PET/CT in PAD. Evidence-based data support the use of [¹⁸F]FDG PET/CT in patients with suspected PAD for investigating an underlying malignancy even if it is still unclear whether [¹⁸F]FDG PET/CT should be performed after negative/inconclusive conventional imaging or as part of the initial workup of PAD.