Structural and Metabolic Features of Two Different Variants of Multiple Sclerosis: A PET/MRI Study

18F-Fluorodeoxy Glucose and 11C-Methionine Accumulation in Demyelinating Lesions

Background Few studies have evaluated the accumulation of 18F-fluorodeoxyglucose (FDG), 11C-methionine (MET), and other positron emission tomography (PET) tracers in patients with demyelinating disease.

Purpose This study aimed to investigate the accumulation of FDG-PET/computed tomography (CT) and MET-PET/CT in demyelinating lesions.

Material and Methods A retrospective search of the patient database in our hospital identified five patients with demyelinating disease in whom PET studies performed in the past 10 years revealed accumulation of FDG or MET. The clinical diagnoses were multiple sclerosis (n=1), myelitis (n=1), limbic encephalitis (n=1), chronic inflammatory demyelinating polyneuropathy (CIDP; n=1), and acute demyelinating encephalomyelitis (ADEM; n=1). Two patients received FDG-PET/CT alone and three patients received both FDG-PET/CT and MET-PET/CT on the same day. Images were visually and conjointly reviewed by two radiologists. In semiquantitative evaluation, the maximum standardized uptake value (SUVmax) of the lesion was measured. The lesion-to-normal brain uptake ratio (L/N ratio) was calculated.

Results FDG and/or MET accumulated to a part of the lesions seen on MRI. SUVmax on FDG-PET/CT ranged from 3.8 to 10.3, and L/N ratio on MET-PET/CT ranged from 16.6 to 2.4.

Conclusion It has been established that neoplastic and demyelinating lesions can be differentiated on the basis of FDG or MET uptake. However, as accumulation of FDG and MET can also occur in demyelinating lesions; knowledge of this possibility is of clinical importance.

Glutathione targeted tragacanthic acid-chitosan as a non-viral vector for brain delivery of miRNA-219a-5P: An in vitro/in vivo study

Multiple sclerosis (MS) is a progressive chronic demyelinating and neurodegenerative disease. The symptoms could only be diminished through stimulated remyelination. Although administration of microRNA-219a-5P (miR-219) seems to recover the damages, it is hampered by the challenging delivery of genes to the central nervous system across the blood-brain barrier. To enhance the CNS delivery of miR-219, a novel non-viral targeted vector was appraised by conjugating chitosan (Ch) to tragacanthic acid (TA) and glutathione (Glu). The nanoparticles were characterized and injected into the cuprizone model of MS mice to investigate the in vivo features of the resulting polyplex. Transmission electron microscopy, luxol fast blue staining, and proteolipid protein 1 (Plp1) overexpression confirmed more compact myelin sheaths following the administration of the targeted miR-219 nanoparticles and positron emission tomography (PET) scan also demonstrated the reduced inflammation and higher cell regeneration in the brain. Fluorescence microscopy and in vivo imaging were employed to identify miR-219 accumulation patterns in mice. The polyplex led to miR-219 overexpression, crystallin alpha B upregulation, and apolipoprotein E downregulation. It was concluded that glutathione targeted Ch/TA nanoparticles could be exploited as a feasible non-viral vector for miR-219 specific targeting to the brain, miR-219 overexpression and inflammation abatement in MS.

Advancements in Positron Emission Tomography/Magnetic Resonance Imaging and Applications to Diagnostic Challenges in Neuroradiology

Since the clinical adoption of magnetic resonance (MR) in medical imaging, MR has proven to be a workhorse in diagnostic neuroradiology, with the ability to provide superb anatomic detail as well as additional functional and physiologic data, depending on the techniques utilized. Positron emission tomography/computed tomography has also shown irreplaceable diagnostic value in certain disease processes of the central nervous system by providing molecular and metabolic information through the development of numerous disease-specific PET tracers, many of which can be utilized as a diagnostic technique in and of themselves or can provide a valuable adjunct to information derived from MR. Despite these advances, many challenges still remain in neuroradiology, particularly in malignancy, neurodegenerative disease, epilepsy, and cerebrovascular disease. Through improvements in attenuation correction, motion correction, and PET detectors, combining the 2 modalities of PET and MR through simultaneous imaging has proven feasible and allows for improved spatial and temporal resolution without compromising either of the 2 individual modalities. The complementary information offered by both technologies has provided increased diagnostic accuracy in both research and many clinical applications in neuroradiology.

The impact of MR-based attenuation correction in spinal cord FDG-PET/MR imaging for neurological studies

Purpose

Positron emission tomography (PET) attenuation correction (AC) in positron emission tomography‐magnetic resonance (PET/MR) scanners constitutes a critical and barely explored issue in spinal cord investigation, mainly due to the limitations in accounting for highly attenuating bone structures which surround the spinal canal. Our study aims at evaluating the clinical suitability of MR‐driven AC (MRAC) for 18‐fluorodeoxy‐glucose positron emission tomography (¹⁸F‐FDG‐PET) in spinal cord.

Methods

Thirty‐six patients, undergoing positron emission tomography‐computed tomography (PET/CT) and PET/MR in the same session for oncological examination, were retrospectively analyzed.

For each patient, raw PET data from PET/MR scanner were reconstructed with 4‐ and 5‐class MRAC maps, generated by hybrid PET/MR system (PET_MRAC4 and PET_MRAC5, respectively, where PET_MRAC is PET images reconstructed using MR‐based attenuation correction map), and an AC map derived from CT data after a custom co‐registration pipeline (PET_rCTAC, where PET_rCTAC is PET images reconstructed using CT‐based attenuation correction map), which served as reference. Mean PET standardized uptake values (SUVm) were extracted from the three reconstructed PET images by regions of interest (ROIs) identified on T2‐weighted MRI, in the spinal cord, lumbar cerebrospinal fluid (CSF), and vertebral marrow at five levels (C2, C5, T6, T12, and L3). SUVm values from PET_MRAC4 and PET_MRAC5 were compared with each other and with the reference by means of paired t‐test, and correlated using Pearson's correlation (r) to assess their consistency. Cohen's d was calculated to assess the magnitude of differences between PET images.

Results

SUVmvalues from PET_MRAC4 were lower than those from PET_MRAC5 in almost all analyzed ROIs, with a mean difference ranging from 0.03 to 0.26 (statistically significant in the vertebral marrow at C2 and C5, spinal cord at T6 and T2, and CSF at L3). This was also confirmed by the effect size, with highest values at low spinal levels (d = 0.45 at T12 in spinal cord, d = 0.95 at L3 in CSF). SUVm values from PET_MRAC4 and PET_MRAC5 showed a very good correlation (0.81 < r < 0.97, p < 0.05) in all spinal ROIs. Underestimation of SUVm between PET_MRAC4 and PET_rCTAC was observed at each level, with a mean difference ranging from 0.02 to 0.32 (statistically significant in the vertebral marrow at C2 and T6, and CSF at L3). Although PET_MRAC5 underestimates PET_rCTAC (mean difference ranging from 0.02 to 0.3), an overall decrease in effect size could be observed for PET_MRAC5, mainly at lower spinal levels (T12, L3). SUVm from both PET_MRAC4 and PET_MRAC5 methods showed r value from good to very good with respect to PET_rCTAC (0.67 < r < 0.9 and 0.73 < r < 0.94, p < 0.05, respectively).

Conclusions

Our results showed that neglecting bones in AC can underestimate the FDG uptake measurement of the spinal cord. The inclusion of bones in MRAC is far from negligible and improves the AC in spinal cord, mainly at low spinal levels. Therefore, care must be taken in the spinal canal region, and the use of AC map reconstruction methods accounting for bone structures could be beneficial.

Baló's concentric sclerosis - A rare entity within the spectrum of demyelinating diseases

Baló's concentric sclerosis (BCS) is a rare, inflammatory demyelinating disease of the central nervous system (CNS). Historically, BCS was thought to be uniformly fatal and diagnosis was based on postmortem findings. With advances in modern neuroimaging, BCS is currently defined by the presence of concentric layered patterns composed of alternating rings of varying intensity. They are best appreciated on gadolinium-enhanced T1-weighted sequences and predominantly occur in the supratentorial cerebral white matter with sparing of cortical U-fibers. The lamellar pattern of the lesions likely reflects bands of demyelination and relative myelin preservation with minimal axonal loss. While BCS falls within the spectrum of atypical demyelinating diseases, there is ongoing debate over whether BCS is a phenotypical variant of multiple sclerosis (MS) or a separate entity. Corticosteroids comprise first-line therapy but there is ongoing controversy regarding appropriate maintenance therapy. First-line MS disease-modifying therapies such as interferon beta-1a are appropriate for patients who fulfill diagnostic criteria for relapsing-remitting MS. Fingolimod should likely be avoided as Baló-like lesions have been reported during its administration or after withdrawal. Monoclonal antibodies such as natalizumab and rituximab are potentially effective at reducing BCS relapses, but alemtuzumab may be relatively ineffective because humoral immunity does not play a central role in BCS pathogenesis.

TSPO PET With 18F-GE-180 to Differentiate Variants of Multiple Sclerosis: Relapsing-Remitting Multiple Sclerosis, Tumefactive Demyelination, and Baló's Concentric Sclerosis

PET targeting the translocator protein (TSPO) expression is an interesting approach to detect neuroinflammation, as TSPO is upregulated in activated macrophages and microglia. Considering the variable pathophysiology of multiple sclerosis (MS) variants, we compare TSPO PET using F-GE-180 in 3 different demyelinating diseases of the central nervous system: relapsing-remitting MS, tumefactive MS, and Baló's concentric sclerosis. Visualization of neuroinflammation and its PET patterns in addition to MRI may contribute to accurate distinction and monitoring of central nervous system demyelination.

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.

From Baló's concentric sclerosis to multiple sclerosis: a series of 6 patients

INTRODUCTION

Baló's concentric sclerosis (BCS) is a rare CNS disorder characterized by alternating bands of demyelination on MRI. One of the main issues is its relationship with multiple sclerosis (MS).

OBJECTIVES

To describe 6 BCS patients. To review the risk of developing MS in BCS patients.

METHODS

We retrospectively recorded clinical and radiological findings of 6 BCS patients and performed a review of the literature.

RESULTS

Six patients (5 women) with a mean age of 25 years old were included. Main symptoms were hemiparesis/hemihypoesthesia. On MRI, two patients had a single BCS lesion and four had additional MS-like lesions. Alternating bands were usually more visible on DWI. A patient had reduced central perfusion and SWI hypointensity suggestive of a central vein. Oligoclonal bands were identified in 5/6 patients. After 7 years of follow-up, all patients achieved MS criteria with mild disability (mean EDSS 1.75; 0-4). Our literature review included 65 BCS patients from 30 studies: although CSF oligoclonal bands and the presence of additional MS lesions were associated with subsequent relapses, this was not significant.

DISCUSSION/CONCLUSION

Our series allows a detailed MRI description in BCS and gives a new insight into BCS evolution and its strong relationship with MS.

Pseudotumoral demyelinating lesions: diagnostic approach and long-term outcome

PURPOSE OF REVIEW

To review the clinical findings, differential diagnosis, treatment and outcome of pseudotumoral demyelinating lesions including tumefactive demyelination and Baló's concentric sclerosis.

RECENT FINDINGS

MRI findings, such as dynamic restricted diffusion changes at the edge of pseudotumoral lesions help to discriminate atypical demyelination from key differential diagnoses, and together with histopathological data, indicate that tissue hypoxia may be important aetiologically. CT-PET imaging can help to distinguish pseudotumoral lesions from high-grade tumours. Although most patients with pseudotumoral lesions have or later develop multiple sclerosis, a proportion will experience a monophasic course or be diagnosed with neuromyelitis optica spectrum disorders (NMOSD), myelin oligodendrocyte glycoprotein (MOG) antibody-associated demyelination or acute disseminated encephalomyelitis (ADEM). Many patients with pseudotumoral demyelinating lesions have a favourable prognosis.

SUMMARY

Not all patients with pseudotumoral lesions require a brain biopsy but close follow-up of biopsied and nonbiopsied lesions is indicated once a diagnosis is established. Testing for AQP4-IgG and MOG-IgG is recommended when a pseudotumoral demyelinating lesion is identified. In the absence of large, prospective studies, it seems reasonable that patients with pseudotumoral lesions who fulfil multiple sclerosis diagnostic criteria are treated with multiple sclerosis therapies.

Molecular imaging of multiple sclerosis: from the clinical demand to novel radiotracers

Background

Brain PET imaging with different tracers is mainly clinically used in the field of neurodegenerative diseases and brain tumors. In recent years, the potential usefulness of PET has also gained attention in the field of MS. In fact, MS is a complex disease and several processes can be selected as a target for PET imaging. The use of PET with several different tracers has been mainly evaluated in the research setting to investigate disease pathophysiology (i.e. phenotypes, monitoring of progression) or to explore its use a surrogate end-point in clinical trials.

Results

We have reviewed PET imaging studies in MS in humans and animal models. Tracers have been grouped according to their pathophysiological targets (ie. tracers for myelin kinetic, neuroinflammation, and neurodegeneration). The emerging clinical indication for brain PET imaging in the differential diagnosis of suspected tumefactive demyelinated plaques as well as the clinical potential provided by PET images in view of the recent introduction of PET/MR technology are also addressed.

Conclusion

While several preclinical and fewer clinical studies have shown results, full-scale clinical development programs are needed to translate molecular imaging technologies into a clinical reality that could ideally fit into current precision medicine perspectives.

PET/MRI in Infection and Inflammation

Hybrid positron emission tomography/magnetic resonance imaging (PET/MR) systems are now more and more available for clinical use. PET/MR combines the unique features of MR including excellent soft tissue contrast, diffusion-weighted imaging, dynamic contrast-enhanced imaging, fMRI and other specialized sequences as well as MR spectroscopy with the quantitative physiologic information that is provided by PET. Most of the evidence of the potential clinical utility of PET/MRI is available for neuroimaging. Other areas, where PET/MR can play a larger role include head and neck, upper abdominal, and pelvic tumours. Although the role of PET/MR in infection and inflammation of the cardiovascular system and in musculoskeletal applications are promising, these areas of clinical investigation are still in the early phase and it may be a little longer before these areas reach their full potential in clinical practice. In this review, we outline the potential of hybrid PET/MR for imaging infection and inflammation. A background to the main radiopharmaceuticals and some technical considerations are also included.

Atypical inflammatory demyelinating lesions and atypical multiple sclerosis

Atypical idiopathic inflammatory demyelinating disorders (IIDDs) of the brain have long been known to be disorders closely related to multiple sclerosis (MS), despite having distinctive clinical and radiological characteristics. Originally, they mostly corresponded to acute-onset variants of MS that classically had poor prognoses, such as Baló's concentric sclerosis, Marburg variant of MS and Schilder's disease, and their relationship with MS was based on their shared pathological findings and the co-occurrence of these variants in patients with typical MS. More recently, other atypical disorders, such as solitary sclerosis, have also been described as belonging to the MS spectrum, raising the question of their links with MS. Meanwhile, multiple MS mimics have been described and need to be considered in the differential diagnosis of MS. In addition, thorough characterization of these atypical entities, including advanced MRI and biological studies, is now warranted to further improve their management.

Molecular and Metabolic Imaging in Multiple Sclerosis

Multiple sclerosis is a multifactorial disease with heterogeneous pathogenetic mechanisms, which deserve to be studied to evaluate new possible targets for treatments and improve patient management. MR spectroscopy and PET allow assessing in vivo the molecular and metabolic mechanisms underlying the pathogenesis of multiple sclerosis. This article focuses on the relationship between these imaging techniques and the biologic and chemical pathways leading to multiple sclerosis pathology and its clinical features. Future directions of research are also presented.

Why Is This Auntminnie a Diagnostic Conundrum?: A Knowledge-Based Approach to Balo's Concentric Sclerosis From Reports of 3 Cases and Pooled Data From 68 Other Patients in the Literature

INTRODUCTION

We came across 3 cases of Balo's concentric sclerosis (BCS). The first of these patients presented to an outside hospital and was transferred to our institution due to complications resulting from a biopsy. The other 2 patients, despite having a characteristic imaging appearance and despite insistence on our part on the diagnosis of BCS, underwent a surgical procedure, which could have been prevented. This led us to review the available literature on BCS.

MATERIAL AND METHODS

A total of 68 patients diagnosed with BCS between 1995 and 2015 were studied and the data collected for the clinical presentation and course, imaging, spinal fluid analysis, treatment, and clinical and imaging outcome.

CONCLUSIONS

A 25% surgery rate (biopsy or resection) was found in the study. We concluded that this relatively high surgery rate in this auntminnie nonsurgical disease is multifactorial; and includes factors like nonfamiliarity with the disease, anxiety on the part of patients and physicians, due to a sometimes rapidly deteriorating clinical picture; and resemblance of the disease with other entities such as tumor and infection. However, characteristic imaging appearance combined with acute or subacute presentation and dramatic improvement in clinical status after high-dose steroid chemotherapy; are highly suggestive of the disease, and can prevent unnecessary surgery.

The Role of Advanced Magnetic Resonance Imaging Techniques in Multiple Sclerosis Clinical Trials

Magnetic resonance imaging has been crucial in the development of anti-inflammatory disease-modifying treatments. The current landscape of multiple sclerosis clinical trials is currently expanding to include testing not only of anti-inflammatory agents, but also neuroprotective, remyelinating, neuromodulating, and restorative therapies. This is especially true of therapies targeting progressive forms of the disease where neurodegeneration is a prominent feature. Imaging techniques of the brain and spinal cord have rapidly evolved in the last decade to permit in vivo characterization of tissue microstructural changes, connectivity, metabolic changes, neuronal loss, glial activity, and demyelination. Advanced magnetic resonance imaging techniques hold significant promise for accelerating the development of different treatment modalities targeting a variety of pathways in MS.

PET/MRI of central nervous system: current status and future perspective

Imaging plays an increasingly important role in the early diagnosis, prognosis prediction and therapy response evaluation of central nervous system (CNS) diseases. The newly emerging hybrid positron emission tomography/magnetic resonance imaging (PET/MRI) can perform "one-stop-shop" evaluation, including anatomic, functional, biochemical and metabolic information, even at the molecular level, for personalised diagnoses and treatments of CNS diseases. However, there are still several problems to be resolved, such as appropriate PET detectors, attenuation correction and so on. This review will introduce the basic physical principles of PET/MRI and its potential clinical applications in the CNS. We also provide the future perspectives for this field.

KEY POINTS

• PET/MRI can simultaneously provide anatomic, functional, biochemical and metabolic information. • PET/MRI has promising potential in various central nervous system diseases. • Research on the future implementation of PET/MRI is challenging and encouraging.

Baló's concentric sclerosis

Baló's concentric sclerosis is often regarded as a rare variant of multiple sclerosis. Patients with this disorder present with acute or subacute neurological deterioration, with MRI showing one or more concentrically multilayered ring-like lesions usually in the cerebral white matter. Historically, Baló's concentric sclerosis was thought fatal in all cases. However, the availability of MRI has led to a better appreciation of the variable natural history of patients presenting with radiologically evident Baló lesions and the clinical association with multiple sclerosis and, less often, with other neurological disorders. Important advances have increased understanding of the immunopathogenic mechanisms associated with the formation of Baló lesions. However, how to treat an acute lesion and when or whether to start treatment are less well understood, although for patients with Baló lesions who also fulfil standard diagnostic criteria for multiple sclerosis, our opinion is that treatment with multiple sclerosis disease-modifying therapy would seem reasonable.

PET imaging in multiple sclerosis

Positron emission tomography (PET) is a non-invasive technique for quantitative imaging of biochemical and physiological processes in animals and humans. PET uses probes labeled with a radioactive isotope, called PET tracers, which can bind to or be converted by a specific biological target and thus can be applied to detect and monitor different aspects of diseases. The number of applications of PET imaging in multiple sclerosis is still limited. Clinical studies using PET are basically focused on monitoring changes in glucose metabolism and the presence of activated microglia/macrophages in sclerotic lesions. In preclinical studies, PET imaging of targets for other processes, like demyelination and remyelination, has been investigated and may soon be translated to clinical applications. Moreover, more PET tracers that could be relevant for MS are available now, but have not been studied in this context yet. In this review, we summarize the PET imaging studies performed in multiple sclerosis up to now. In addition, we will identify potential applications of PET imaging of processes or targets that are of interest to MS research, but have yet remained largely unexplored.

Atypical idiopathic inflammatory demyelinating lesions: prognostic implications and relation to multiple sclerosis

Atypical lesions of a presumably idiopathic inflammatory demyelinating origin present quite variably and may pose diagnostic problems. The subsequent clinical course is also uncertain. We, therefore, wanted to clarify if atypical idiopathic inflammatory demyelinating lesions (AIIDLs) can be classified according to previously suggested radiologic characteristics and how this classification relates to prognosis. Searching the databases of eight tertiary referral centres we identified 90 adult patients (61 women, 29 men; mean age 34 years) with ≥ 1 AIIDL. We collected their demographic, clinical and magnetic resonance imaging data and obtained follow-up (FU) information on 77 of these patients over a mean duration of 4 years. The AIIDLs presented as a single lesion in 72 (80 %) patients and exhibited an infiltrative (n = 35), megacystic (n = 16), Baló (n = 10) or ring-like (n = 16) lesion appearance in 77 (86 %) patients. Additional multiple sclerosis (MS)-typical lesions existed in 48 (53 %) patients. During FU, a further clinical attack occurred rarely (23-35 % of patients) except for patients with ring-like AIIDLs (62 %). Further attacks were also significantly more often in patients with coexisting MS-typical lesions (41 vs. 10 %, p < 0.005). New AIIDLs developed in six (7 %), and new MS-typical lesions in 29 (42 %) patients. Our findings confirm the previously reported subtypes of AIIDLs. Most types confer a relatively low risk of further clinical attacks, except for ring-like lesions and the combination with MS-typical lesions.