18F-FDG-PET/MRI in the diagnostic work-up of limbic encephalitis

Clinical Value of Hybrid PET/MR Imaging: Brain Imaging Using PET/MR Imaging

Hybrid PET/MR imaging offers a unique opportunity to acquire MR imaging and PET information during a single imaging session. PET/MR imaging has numerous advantages, including enhanced diagnostic accuracy, improved disease characterization, and better treatment planning and monitoring. It enables the immediate integration of anatomic, functional, and metabolic imaging information, allowing for personalized characterization and monitoring of neurologic diseases. This review presents recent advances in PET/MR imaging and highlights advantages in clinical practice for neuro-oncology, epilepsy, and neurodegenerative disorders. PET/MR imaging provides valuable information about brain tumor metabolism, perfusion, and anatomic features, aiding in accurate delineation, treatment response assessment, and prognostication.

Utility of hybrid PET/MRI in stereoelectroencephalography guided radiofrequency thermocoagulation in MRI negative epilepsy patients

Introduction

Hybrid positron emission tomography/magnetic resonance imaging (PET/MRI) is a novel advanced non-invasive presurgical examination tool for patients with drug-resistant epilepsy (DRE). This study aims to evaluate the utility of PET/MRI in patients with DRE who undergo stereoelectroencephalography-guided radiofrequency thermocoagulation (SEEG-guided RFTC).

Methods

This retrospective study included 27 patients with DRE who underwent hybrid PET/MRI and SEEG-guided RFTC. Surgery outcome was assessed using a modified Engel classification, 2 years after RFTC. Potential areas of the seizure onset zone (SOZ) were identified on PET/MRI and confirmed by SEEG.

Results

Fifteen patients (55%) became seizure-free after SEEG-guided RFTC. Engel class II, III, and IV were achieved in six, two, and four patients, respectively at the 2 years follow-up. MRI was negative in 23 patients and structural abnormalities were found in four patients. Hybrid PET/MRI contributed to the identification of new structural or metabolic lesions in 22 patients. Concordant results between PET/MRI and SEEG were found in 19 patients in the identification of SOZ. Among the patients with multifocal onset, seizure-free status was achieved in 50% (6/12).

Conclusion

SEEG-guided RFTC is an effective and safe treatment for drug-resistant epilepsy. Hybrid PET/MRI serves as a useful tool for detecting the potential SOZs in MRI-negative patients and guide the implantation of SEEG electrodes. Patients with multifocal epilepsy may also benefit from this palliative treatment.

Approach to acute encephalitis in the intensive care unit

PURPOSE OF REVIEW

Recent years have seen a dramatic increase in the identification of autoimmune encephalitis (AE) and the emergence of new causes of infectious encephalitis (IE). However, management of these patients remains challenging, with many requiring care in intensive care units. Here, we describe recent advances in the diagnosis and management of acute encephalitis.

RECENT FINDINGS

Advances in the identification of clinical presentations, neuroimaging biomarkers, and electroencephalogram patterns have enabled more rapid diagnosis of encephalitis. Newer modalities such as meningitis/encephalitis multiplex PCR panels, metagenomic next-generation sequencing, and phage display-based assays are being evaluated in an effort to improve detection of autoantibodies and pathogens. Specific advances in the treatment of AE include establishment of a systematic approach to first-line therapies and the development of newer second-line modalities. The role of immunomodulation and its applications in IE are actively being investigated. In the ICU, particular attention to status epilepticus, cerebral edema, and dysautonomia may improve outcomes.

SUMMARY

Substantial diagnostic delays still occur, with many cases left without an identified etiology. Antiviral therapies remain scarce, and optimal treatment regimens for AE still need to be clarified. Nevertheless, our understanding of diagnostic and therapeutic approaches to encephalitis is rapidly evolving.

Brain Metabolic Alterations in Seropositive Autoimmune Encephalitis: An 18F-FDG PET Study

INTRODUCTION

Autoimmune encephalitis (AE) diagnosis and follow-up remain challenging. Brain ¹⁸F-fluoro-deoxy-glucose positron emission tomography (FDG PET) has shown promising results in AE. Our aim was to investigate FDG PET alterations in AE, according to antibody subtype.

METHODS

We retrospectively included patients with available FDG PET and seropositive AE diagnosed in our center between 2015 and 2020. Brain PET Z-score maps (relative to age matched controls) were analyzed, considering metabolic changes significant if |Z-score| ≥ 2.

RESULTS

Forty-six patients were included (49.4 yrs [18; 81]): 13 with GAD autoantibodies, 11 with anti-LGI1, 9 with NMDAR, 5 with CASPR2, and 8 with other antibodies. Brain PET was abnormal in 98% of patients versus 53% for MRI. The most frequent abnormalities were medial temporal lobe (MTL) and/or striatum hypermetabolism (52% and 43% respectively), cortical hypometabolism (78%), and cerebellum abnormalities (70%). LGI1 AE tended to have more frequent MTL hypermetabolism. NMDAR AE was prone to widespread cortical hypometabolism. Fewer abnormalities were observed in GAD AE. Striatum hypermetabolism was more frequent in patients treated for less than 1 month (p = 0.014), suggesting a relation to disease activity.

CONCLUSION

FDG PET could serve as an imaging biomarker for early diagnosis and follow-up in AE.

Pediatric neuropsychiatric disorders with motor and nonmotor phenomena

The concept of pediatric autoimmune neuropsychiatric disorders associated with group A beta-hemolytic streptococcus (PANDAS) has become seminal since first introduced more than two decades ago. At the time of this writing, most neurologists, pediatricians, psychiatrists, and general pediatricians will probably have heard of this association or treated an affected child with PANDAS. The concept of an acute-onset, and typically self-limited, postinfectious autoimmune neuropsychiatric disorder resembling PANDAS manifesting vocal and motor tics and obsessive-compulsive disorder has broadened to other putative microbes and related endogenous and exogenous disease triggers. These disorders with common features of hypometabolism in the medial temporal lobe and hippocampus in brain 18fluorodeoxyglucose positron emission tomography fused to magnetic resonance imaging (FDG PET-MRI), form a spectrum: with the neuropsychiatric disorder Tourette syndrome and PANDAS with its well-defined etiopathogenesis at one end, and pediatric abrupt-onset neuropsychiatric syndrome (PANS), alone or associated with specific bacterial and viral pathogens, at the other end. The designation of PANS in the absence of a specific trigger, as an exclusionary diagnosis, reflects the current problem in nosology.

Hybrid PET/MRI in Infection and Inflammation: An Update About the Latest Available Literature Evidence

PET/MRI has been reported to be promising in the diagnosis and evaluation of infection and inflammation including brain disorders, bone and soft tissue infections and inflammations, cardiovascular, abdominal, and systemic diseases. However, evidence came out manly from anecdotal cases or small cohorts. The present review aimed to update the latest available evidence about the role of PET/MRI in infection and inflammation. The search (January, 1 2018-July, 8 2022) on PubMed produced 504 results. Sixty-five articles were selected and included in the qualitative synthesis. The number of publications on PET/MRI in the 3 years 2018-2020 was comparable, while it increased in 2021 and 2022 (from 11 to 17 and 15, respectively). [¹⁸F]FDG and ⁶⁸Ga-DOTA-FAPI-04 were the most frequently used (42/65) and innovative radiopharmaceuticals, respectively. [¹⁸F]fluoride (9/65), translocator protein (TSPO)-targeted PET agents (6/65), CXCR4 receptor targeting tracer and β-amyloid plaques binding radiopharmaceuticals (2/65 and 2/65, respectively) were also used. Most PET/MRI studies in the period 2018-2022 focused on inflammation (55/65), and cardiovascular diseases represented the most frequent field of interest (30/65), also when considering each year singularly. An increasing trend in bone and joint publications was observed in the considered period (12/65). Other topics included neurology (11/65), inflammatory bowel disease (8/65), and other (4/65). PET/MRI technology demonstrated to be useful in infection and inflammation, being superior to each single modality and/or facilitating diagnosis in a number of conditions (eg, cardiac sarcoidosis, myocarditis, endocarditis), and/or allowing to provide insightful information about disease biology and apply innovative radiopharmaceuticals (eg, neurology, atherosclerosis). Publications focused on PET/MRI in large vessel vasculitis and aortic diseases include both diagnostic and discovery objectives. The current review corroborates the potential of PET/MRI - combining in a single examination the high soft tissue contrast, high resolution, and functional information of MRI, with molecular data provided by PET technology - to positively impact on the management of infectious diseases and inflammatory conditions.

FDG-PET in Autoimmune Encephalitis: Utility, Pattern of Abnormalities, and Correlation with Autoantibodies

Background

Fluorodeoxyglucose-positron emission tomography (FDG-PET) in autoimmune encephalitis (AE) as an adjunctive investigation helps in characterizing the type of AE based on characteristic metabolic patterns.

Objectives

We aimed to study the following: (i) the sensitivity of FDG-PET in the diagnosis of AE, (ii) describe abnormal patterns of metabolism of various subtypes of AE, and (iii) correlate serum serology with FDG-PET abnormalities.

Materials and Methods

This study was conducted at a tertiary university hospital in South India. The demographic profile, clinical features, and investigations (FDG-PET, magnetic resonance imaging (MRI) brain, electroencephalography (EEG), cerebrospinal fluid (CSF)) were reviewed. The nuclear medicine physician performed blinded qualitative visual and semi-quantitative analysis of the 18-FDG-PET (fluorine 18-FDG-PET) findings of these patients.

Results

Twenty-nine (M:F: 11:18) patients were recruited; among them, 22 (75.8%) patients had autoimmune antibodies; the rest seven (24.1%) patients were seronegative. Among the 22 seropositive patients, 9 (31%) patients were positive for anti-N-methyl-D-aspartate receptor (NMDAR), 8 (28%) for anti-leucine-rich glioma inactivated 1 (LGI-1), 4 (14%) for anti-contactin-associated protein 2 (CASPR2), 1 (3%) for anti-glutamic acid decarboxylase (GAD)-65, and rest 7 (24%) patients were seronegative. The patterns most commonly observed were isolated hypermetabolism (41%), isolated hypometabolism (41%), and combined hypermetabolism with hypometabolism (18%). The fraction of abnormalities was lower for MRI (17/22; 73.9%) than for FDG-PET (27/29; 93.1%). FDG-PET correlated with serology in 10 (34%) cases [NMDAR: 6 (60%) and LGI-1: 4 (40%)]. The sensitivity of FDG-PET was 94.1% when compared with MRI.

Discussion and Conclusion

FDG-PET correlated with serology in only one-third of patients. The most consistent pattern in both seropositive and seronegative AE is characterized by parieto-occipital hypometabolism and fronto-temporal with basal ganglia hypermetabolism.

Positron emission tomography in autoimmune encephalitis: Clinical implications and future directions

¹⁸ F-fluoro-deoxyglucose position emission tomography (¹⁸ F-FDG-PET) has been proven as a sensitive and reliable tool for diagnosis of autoimmune encephalitis (AE). More attention was paid to this kind of imaging because of the shortage of MRI, EEG, and CSF findings. FDG-PET has been assessed in a few small studies and case reports showing apparent abnormalities in cases where MRI does not. Here, we summarized the patterns (specific or not) in AE with different antibodies detected and the clinical outlook for the wide application of FDG-PET considering some limitations. Specific patterns based on antibody subtypes and clinical symptoms were critical for identifying suspicious AE, the most common of which was the anteroposterior gradient in anti- N -methyl- d -aspartate receptor (NMDAR) encephalitis and the medial temporal lobe hypermetabolism in limbic encephalitis. And the dynamic changes of metabolic presentations in different phases provided us the potential to inspect the evolution of AE and predict the functional outcomes. Except for the visual assessment, quantitative analysis was recently reported in some voxel-based studies of regions of interest, which suggested some clues of the future evaluation of metabolic abnormalities. Large prospective studies need to be conducted controlling the time from symptom onset to examination with the same standard of FDG-PET scanning.

[18F]FDG brain PET and clinical symptoms in different autoantibodies of autoimmune encephalitis: a systematic review

INTRODUCTION

Autoimmune encephalitis (AE) is caused by the antibodies that target receptors and intracellular or surface proteins. To achieve the appropriate therapeutic results, early and proper diagnosis is still the most important issue. In this review, we provide an overview of FDG-PET imaging findings in AE patients and possible relation to different subtypes and clinical features.

METHODS

PubMed, Web of Science, and Scopus were searched in August 2021 using a predefined search strategy.

RESULTS

After two-step reviewing, 22 studies with a total of 332 participants were entered into our qualitative synthesis. In anti-NMDAR encephalitis, decreased activity in the occipital lobe was present, in addition, to an increase in frontal, parietal, and specifically medial temporal activity. Anti-VGKC patients showed altered metabolism in cortical and subcortical regions such as striata and cerebellum. Abnormal metabolism in patients with anti-LGI1 has been reported in diverse areas of the brain including medial temporal, hippocampus, cerebellum, and basal ganglia all of which had hypermetabolism. Hypometabolism in parietal, frontal, occipital lobes, temporal, frontal, and hippocampus was observed in AE patients with anti-GAD antibodies.

CONCLUSION

Our results indicate huge diversity in metabolic patterns among different AE subtypes and it is hard to draw a firm conclusion. Moreover, the timing of imaging, seizures, and acute treatments can alter the PET patterns strongly. Further prospective investigations with specific inclusion and exclusion criteria should be carried out to identify the metabolic defect in different AE subtypes.

Immunological causes of obsessive-compulsive disorder: is it time for the concept of an "autoimmune OCD" subtype?

Obsessive-compulsive disorder (OCD) is a highly disabling mental illness that can be divided into frequent primary and rarer organic secondary forms. Its association with secondary autoimmune triggers was introduced through the discovery of Pediatric Autoimmune Neuropsychiatric Disorder Associated with Streptococcal infection (PANDAS) and Pediatric Acute onset Neuropsychiatric Syndrome (PANS). Autoimmune encephalitis and systemic autoimmune diseases or other autoimmune brain diseases, such as multiple sclerosis, have also been reported to sometimes present with obsessive-compulsive symptoms (OCS). Subgroups of patients with OCD show elevated proinflammatory cytokines and autoantibodies against targets that include the basal ganglia. In this conceptual review paper, the clinical manifestations, pathophysiological considerations, diagnostic investigations, and treatment approaches of immune-related secondary OCD are summarized. The novel concept of "autoimmune OCD" is proposed for a small subgroup of OCD patients, and clinical signs based on the PANDAS/PANS criteria and from recent experience with autoimmune encephalitis and autoimmune psychosis are suggested. Red flag signs for "autoimmune OCD" could include (sub)acute onset, unusual age of onset, atypical presentation of OCS with neuropsychiatric features (e.g., disproportionate cognitive deficits) or accompanying neurological symptoms (e.g., movement disorders), autonomic dysfunction, treatment resistance, associations of symptom onset with infections such as group A streptococcus, comorbid autoimmune diseases or malignancies. Clinical investigations may also reveal alterations such as increased levels of anti-basal ganglia or dopamine receptor antibodies or inflammatory changes in the basal ganglia in neuroimaging. Based on these red flag signs, the criteria for a possible, probable, and definite autoimmune OCD subtype are proposed.

Clinical manifestations and immunomodulatory treatment experiences in psychiatric patients with suspected autoimmune encephalitis: a case series of 91 patients from Germany

Autoimmune encephalitis (AE) can rarely manifest as a predominantly psychiatric syndrome without overt neurological symptoms. This study's aim was to characterize psychiatric patients with AE; therefore, anonymized data on patients with suspected AE with predominantly or isolated psychiatric syndromes were retrospectively collected. Patients with readily detectable neurological symptoms suggestive of AE (e.g., epileptic seizures) were excluded. Patients were classified as "probable psychiatric AE (pAE)," if well-characterized neuronal IgG autoantibodies were detected or "possible pAE" (e.g., with detection of nonclassical neuronal autoantibodies or compatible cerebrospinal fluid (CSF) changes). Of the 91 patients included, 21 (23%) fulfilled our criteria for probable (autoantibody-defined) pAE and 70 (77%) those for possible pAE. Among patients with probable pAE, 90% had anti-NMDA receptor (NMDA-R) autoantibodies. Overall, most patients suffered from paranoid-hallucinatory syndromes (53%). Patients with probable pAE suffered more often from disorientation (p < 0.001) and impaired memory (p = 0.001) than patients with possible pAE. Immunotherapies were performed in 69% of all cases, mostly with high-dose corticosteroids. Altogether, 93% of the patients with probable pAE and 80% of patients with possible pAE reportedly benefited from immunotherapies (p = 0.251). In summary, this explorative, cross-sectional evaluation confirms that autoantibody-associated AE syndromes can predominantly manifest as psychiatric syndromes, especially in anti-NMDA-R encephalitis. However, in three out of four patients, diagnosis of possible pAE was based on nonspecific findings (e.g., slight CSF pleocytosis), and well-characterized neuronal autoantibodies were absent. As such, the spectrum of psychiatric syndromes potentially responding to immunotherapies seems not to be limited to currently known autoantibody-associated AE. Further trials are needed.

Limbic encephalitis

Limbic encephalitis (LE) is a clinical syndrome defined by subacutely evolving limbic signs and symptoms with structural and functional evidence of mediotemporal damage in the absence of a better explanation than an autoimmune (or paraneoplastic) cause. There are features common to all forms of LE. In recent years, antibody(ab)-defined subtypes have been established. They are distinct regarding underlying pathophysiologic processes, clinical and magnetic resonance imaging courses, cerebrospinal fluid signatures, treatment responsivity, and likelihood of a chronic course. With immunotherapy, LE with abs against surface antigens has a better outcome than LE with abs to intracellular antigens. Diagnostic and treatment challenges are, on the one hand, to avoid overlooking and undertreatment and, on the other hand, to avoid overdiagnoses and overtreatment. LE can be conceptualized as a model disease for the consequences of new onset mediotemporal damage by different mechanisms in adult life. It may be studied as an example of mediotemporal epileptogenesis.

Brain 18F-FDG PET for the diagnosis of autoimmune encephalitis: a systematic review and a meta-analysis

OBJECTIVE

To consolidate current understanding of detection sensitivity of brain ¹⁸F-FDG PET scans in the diagnosis of autoimmune encephalitis and to define specific metabolic imaging patterns for the most frequently occurring autoantibodies.

METHODS

A systematic and exhaustive search of data available in the literature was performed by querying the PubMed/MEDLINE and Cochrane databases for the search terms: ((PET) OR (positron emission tomography)) AND ((FDG) OR (fluorodeoxyglucose)) AND ((encephalitis) OR (brain inflammation)). Studies had to satisfy the following criteria: (i) include at least ten pediatric or adult patients suspected or diagnosed with autoimmune encephalitis according to the current recommendations, (ii) specifically present ¹⁸F-FDG PET and/or morphologic imaging findings. The diagnostic ¹⁸F-FDG PET detection sensitivity in autoimmune encephalitis was determined for all cases reported in this systematic review, according to a meta-analysis following the PRISMA method, and selected publication quality was assessed with the QUADAS-2 tool.

RESULTS

The search strategy identified 626 articles including references from publications. The detection sensitivity of ¹⁸F-FDG PET was 87% (80-92%) based on 21 publications and 444 patients included in the meta-analysis. We also report specific brain ¹⁸F-FDG PET imaging patterns for the main encephalitis autoantibody subtypes.

CONCLUSION AND RELEVANCE

Brain ¹⁸F-FDG PET has a high detection sensitivity and should be included in future diagnostic autoimmune encephalitis recommendations. Specific metabolic ¹⁸F-FDG PET patterns corresponding to the main autoimmune encephalitis autoantibody subtypes further enhance the value of this diagnostic.

18 F-FDG-PET/MRI in patients with Graves' orbitopathy

PURPOSE

Currently, therapeutic management of patients with Graves' orbitopathy (GO) relies on clinical assessments and MRI. However, monitoring of inflammation remains difficult since external inflammatory signs do not necessarily represent the orbital disease activity. Therefore, we aimed to evaluate the diagnostic value of ¹⁸F-FDG-PET/MRI to assess the inflammation of GO patients.

METHODS

Enrolled patients with new onset of GO underwent ophthalmological examinations to evaluate the activity (CAS) and severity of GO (NOSPECS), as well as an ¹⁸F-FDG-PET/MRI (Siemens Biograph mMR) with dual time point imaging (immediately post-injection and 60 min p.i.). A subset of PET parameters including maximum standardized uptake value (SUVmax), metabolic target volume (MTV), and total lesion glycolysis (TLG) were obtained separately per eye and per extraocular eye muscle (EOM). EOM thickness was measured on the co-registered MRI.

RESULTS

Of 14 enrolled patients, three showed mild, seven moderate-to-severe, and four sight-threatening GO. Patients with severe GO showed statistically significant higher TLG than patients with mild GO (p = 0.02) and higher MTV than patients with mild (p = 0.03) and moderate (p = 0.04) GO. Correlation between NOSPECS on one hand and MTV and TLG on the other was significant (R² = 0.49-0.61).

CONCLUSION

TLG and MTV derived from FDG-PET appear to be good discriminators for severe vs. mild-to-moderate GO and show a significant correlation with NOSPECS. As expected, PET parameters of individual eye muscles were not correlated with associated eye motility, since fibrosis, and not inflammation, is mainly responsible for restricted motility. In conclusion, ¹⁸F-FDG-PET/MRI can be used for assessment of GO inflammation.

PET Imaging of Translocator Protein as a Marker of Malaria-Associated Lung Inflammation

Purpose. Malaria-associated acute respiratory distress syndrome (MA-ARDS) is a severe complication of malaria despite effective anti-malarial treatment. Currently, non-invasive imaging procedures such as chest X-rays are used to assess oedema in established MA-ARDS but earlier detection methods are needed to reduce morbidity and mortality. The early stages of MA-ARDS are characterized by the infiltration of leukocytes, in particular monocyte/macrophages, thus monitoring of immune infiltrates may provide a useful indicator of early pathology. Procedures. Plasmodium berghei ANKA-infected C57BL/6 mice, a rodent malaria model of MA-ARDS, were longitudinally imaged using the TSPO imaging agent [¹⁸F]FEPPA as a marker of macrophage accumulation during the development of pathology and response to combined artesunate and chloroquine diphosphate therapy (ART+CQ). [¹⁸F]FEPPA uptake was compared to blood parasitemia levels and pulmonary immune cell infiltrates using flow cytometry. Results. Infected animals showed rapid increases lung retention of [¹⁸F]FEPPA, correlating well with increases in blood parasitemia and pulmonary accumulation of interstitial inflammatory macrophages and MHC II+ alveolar macrophages. Treatment with ART+CQ therapy abrogated this increase in parasitemia and significantly reduced both lung uptake of [¹⁸F]FEPPA and macrophage infiltrates. Conclusions. Retention of [¹⁸F]FEPPA in the lungs is well correlated with changes in blood parasitemia and lung associated macrophages during disease progression and in response to ART+CQ therapy. With further development TSPO biomarkers may have the potential to be able to accurately assess early onset of MA-ARDS.

State of the art of 18F-FDG PET/CT application in inflammation and infection: a guide for image acquisition and interpretation

AIM

The diagnosis, severity and extent of a sterile inflammation or a septic infection could be challenging since there is not one single test able to achieve an accurate diagnosis. The clinical use of 18F-fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT) imaging in the assessment of inflammation and infection is increasing worldwide. The purpose of this paper is to achieve an Italian consensus document on [¹⁸F]FDG PET/CT or PET/MRI in inflammatory and infectious diseases, such as osteomyelitis (OM), prosthetic joint infections (PJI), infective endocarditis (IE), prosthetic valve endocarditis (PVE), cardiac implantable electronic device infections (CIEDI), systemic and cardiac sarcoidosis (SS/CS), diabetic foot (DF), fungal infections (FI), tuberculosis (TBC), fever and inflammation of unknown origin (FUO/IUO), pediatric infections (PI), inflammatory bowel diseases (IBD), spine infections (SI), vascular graft infections (VGI), large vessel vasculitis (LVV), retroperitoneal fibrosis (RF) and COVID-19 infections.

METHODS

In September 2020, the inflammatory and infectious diseases focus group (IIFG) of the Italian Association of Nuclear Medicine (AIMN) proposed to realize a procedural paper about the clinical applications of [¹⁸F]FDG PET/CT or PET/MRI in inflammatory and infectious diseases. The project was carried out thanks to the collaboration of 13 Italian nuclear medicine centers, with a consolidate experience in this field. With the endorsement of AIMN, IIFG contacted each center, and the pediatric diseases focus group (PDFC). IIFG provided for each team involved, a draft with essential information regarding the execution of [¹⁸F]FDG PET/CT or PET/MRI scan (i.e., indications, patient preparation, standard or specific acquisition modalities, interpretation criteria, reporting methods, pitfalls and artifacts), by limiting the literature research to the last 20 years. Moreover, some clinical cases were required from each center, to underline the teaching points. Time for the collection of each report was from October to December 2020.

RESULTS

Overall, we summarized 291 scientific papers and guidelines published between 1998 and 2021. Papers were divided in several sub-topics and summarized in the following paragraphs: clinical indications, image interpretation criteria, future perspectivess and new trends (for each single disease), while patient preparation, image acquisition, possible pitfalls and reporting modalities were described afterwards. Moreover, a specific section was dedicated to pediatric and PET/MRI indications. A collection of images was described for each indication.

CONCLUSIONS

Currently, [¹⁸F]FDG PET/CT in oncology is globally accepted and standardized in main diagnostic algorithms for neoplasms. In recent years, the ever-closer collaboration among different European associations has tried to overcome the absence of a standardization also in the field of inflammation and infections. The collaboration of several nuclear medicine centers with a long experience in this field, as well as among different AIMN focus groups represents a further attempt in this direction. We hope that this document will be the basis for a "common nuclear physicians' language" throughout all the country.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40336-021-00445-w.

Metabolic scoring in autoimmune epilepsy-Should APE scores be modified?

OBJECTIVE

We evaluate the potential utility of F-18 FDG-PET in addition to MRI in the diagnostic work-up of patients with autoimmune epilepsy (AE) and propose the inclusion of functional imaging in the antibody prevalence in epilepsy (APE) scoring system.

METHODS

This was a retrospective analysis in 60 patients, diagnosed and treated for AE, of whom 40 were antibody negative (presumed AE) and 20 were antibody positive (definitive AE). All patients had undergone a dedicated brain and whole body FDG-PET in the department of Nuclear Medicine.

RESULTS

In the antibody negative group, MRI supported a diagnosis of AE in 23 patients. Both MRI and PET were indicative in 12 cases, and standalone PET was positive in 8. While MRI alone was diagnostic in 57% (23/40), the combined yield of both modalities was 77% (31/40). When PET scores were added to assign the APE score in MRI negative cases, average APE score was 5.4. In the antibody positive group, MRI supported the diagnosis of AE in 7 patients. Both MRI and PET were positive in 4 patients and standalone PET was positive in 5 patients. While MRI alone was diagnostic in 35% (7/20), the combined yield of both modalities was 60% (12/20). When PET scores were added to assign the APE score in MRI negative cases, average APE score was 6.1.

CONCLUSION

The inclusion of metabolic information from PET distinctly improved (the sensitivity of) APE scores to predict autoimmune origin even in antibody negative cases. A larger prospective study of similar type could justify adoption of FDG-PET into the standard diagnostic procedure.

18F-FDG PET Imaging Predicts the Epileptogenic Zone Prospectively in Recurrent Cryptogenic Meningoencephalitis with Subsequent Simple Partial Visual Seizures

¹⁸F-FDG PET scans have proven to be useful in the diagnosis and management of encephalitis patients. ¹⁸F-FDG PET scans are also the standard of care in the evaluation of epilepsy patients before surgery. Encephalitis patients who later develop epilepsy may have useful imaging findings at the time of diagnosis. We present a case of ¹⁸F-FDG PET imaging in a patient with recurrent cryptogenic meningoencephalitis. ¹⁸F-FDG PET imaging after resolution of the encephalitis revealed hypometabolism in previously hypermetabolic areas. Hence, the initial ¹⁸F-FDG PET scan prospectively predicted the epileptogenic zone and seizure-onset zone.

COVID-19-related encephalopathy: a case series with brain FDG-positron-emission tomography/computed tomography findings

Aim

The aim of this paper is to describe the clinical features of COVID‐19‐related encephalopathy and their metabolic correlates using brain 2‐desoxy‐2‐fluoro‐D‐glucose (FDG)‐positron‐emission tomography (PET)/computed tomography (CT) imaging.

Background and purpose

A variety of neurological manifestations have been reported in association with COVID‐19. COVID‐19‐related encephalopathy has seldom been reported and studied.

Methods

We report four cases of COVID‐19‐related encephalopathy. The diagnosis was made in patients with confirmed COVID‐19 who presented with new‐onset cognitive disturbances, central focal neurological signs, or seizures. All patients underwent cognitive screening, brain magnetic resonance imaging (MRI), lumbar puncture, and brain 2‐desoxy‐2‐fluoro‐D‐glucose (FDG)‐positron‐emission tomography (PET)/computed tomography (CT) (FDG‐PET/CT).

Results

The four patients were aged 60 years or older, and presented with various degrees of cognitive impairment, with predominant frontal lobe impairment. Two patients presented with cerebellar syndrome, one patient had myoclonus, one had psychiatric manifestations, and one had status epilepticus. The delay between first COVID‐19 symptoms and onset of neurological symptoms was between 0 and 12 days. None of the patients had MRI features of encephalitis nor significant cerebrospinal fluid (CSF) abnormalities. SARS‐CoV‐2 RT‐PCR in the CSF was negative for all patients. All patients presented with a consistent brain FDG‐PET/CT pattern of abnormalities, namely frontal hypometabolism and cerebellar hypermetabolism. All patients improved after immunotherapy.

Conclusions

Despite varied clinical presentations, all patients presented with a consistent FDG‐PET pattern, which may reflect an immune mechanism.

Contribution of PET-MRI in brain diseases in clinical practice

PURPOSE OF REVIEW

Hybrid PET- MRI is a technique that has the ability to improve diagnostic accuracy in many applications, whereas PET and MRI performed separately often fail to provide accurate responses to clinical questions. Here, we review recent studies and current developments in PET-MRI, focusing on clinical applications.

RECENT FINDINGS

The combination of PET and MRI imaging methods aims at increasing the potential of each individual modality. Combined methods of image reconstruction and correction of PET-MRI attenuation are being developed, and a number of applications are being introduced into clinical practice. To date, the value of PET-MRI has been demonstrated for the evaluation of brain tumours in epilepsy and neurodegenerative diseases. Continued advances in data analysis regularly improve the efficiency and the potential application of multimodal biomarkers.

SUMMARY

PET-MRI provides simultaneous of anatomical, functional, biochemical and metabolic information for the personalized characterization and monitoring of neurological diseases. In this review, we show the advantage of the complementarity of different biomarkers obtained using PET-MRI data. We also present the recent advances made in this hybrid imaging modality and its advantages in clinical practice compared with MRI and PET separately.

Utility of brain fluorodeoxyglucose PET in children with possible autoimmune encephalitis

PURPOSE

We aimed to explore the utility and additional clinical contribution of brain fluorodeoxyglucose (FDG) PET imaging for the assessment of children with possible autoimmune encephalitis in comparison to brain MRI.

MATERIALS AND METHODS

We conducted a retrospective analysis of six pediatric patients (all seronegative) between 2014 and 2019 with the initial diagnosis of possible autoimmune encephalitis who had brain FDG PET/CT or PET/MRI and brain MRI during the diagnostic period. Diagnosis of possible autoimmune encephalitis was based on clinical consensus criteria defined by Graus et al. Brain FDG PET images were visually evaluated. Semiquantitative evaluation was also performed by using the statistical parametric mapping (SPM) method.

RESULTS

Cerebrospinal fluid pleiocytosis and electroencephalography abnormality were present in all patients. Mean duration between the onset of symptoms and brain FDG PET imaging was 33 ± 16 days (range: 18-62 days). There were a total of eight brain FDG PET scans (six of PET/MRI and two of PET/CT). In two patients, FDG PET imaging was performed at diagnosis and follow-up. Initial FDG PET and SPM analysis findings were abnormal in all patients (100%), with four demonstrating only hypometabolism. Only a hypermetabolic pattern was seen in one patient, and mixed the hypohypermetabolic pattern was seen in one patient. All patients had metabolic abnormalities in temporal lobes. Additionally, visual and semiquantitative FDG PET findings revealed hypometabolism in extratemporal regions. Brain MRI was abnormal in two patients (33.3%) who had also FDG hypermetabolism in mesial temporal lobes.

CONCLUSIONS

Our findings support the usage of fluorine-18-FDG PET/computed tomography (CT)/MRI with quantitative analysis early in the diagnostic work-up of possible autoimmune encephalitis, particularly in those with normal or nonspecific MRI findings. However, it remains a purpose of further studies, if and to what extent FDG PET/CT or integrated FDG PET/MRI with quantitative analysis can improve the diagnostic workup of children with possible autoimmune encephalitis.