Prolonged viral pneumonia and high mortality in COVID-19 patients on anti-CD20 monoclonal antibody therapy.

PURPOSE: In clinical practice, we observed an apparent overrepresentation of COVID-19 patients on anti-CD20 monoclonal antibody therapy. The aim of this study was to characterize the clinical picture of COVID-19 in these patients. METHODS: All adult patients from Turku University Hospital, Turku, Finland, with COVID-19 diagnosis and/or positive SARS-CoV-2 PCR test result up to March 2023, and with anti-CD20 therapy within 12 months before COVID-19 were included. Data was retrospectively obtained from electronic patient records. RESULTS: Ninety-eight patients were identified. 44/93 patients (47.3%) were hospitalized due to COVID-19. Patients with demyelinating disorder (n = 20) were youngest (median age 36.5 years, interquartile range 33-45 years), had less comorbidities, and were least likely to be hospitalized (2/20; 10.0%) or die (n = 0). COVID-19 mortality was 13.3% in the whole group, with age and male sex as independent risk factors. Persistent symptoms were documented in 33/94 patients (35.1%) alive by day 30, in 21/89 patients (23.6%) after 60 days, and in 15/85 after 90 days (17.6%), mostly in patients with haematological malignancy or connective tissue disease. Prolonged symptoms after 60 days predisposed to persistent radiological findings (odds ratio 64.0; 95% confidence interval 6.3-711; p < 0.0001) and persistently positive PCR (odds ratio 45.5, 95% confidence interval 4.0-535; p < 0.0001). Several patients displayed rapid response to late antiviral therapy. CONCLUSION: Anti-CD20 monoclonal antibody therapy is associated with high COVID-19 mortality and with a phenotype consistent with prolonged viral pneumonia. Our study provides rationale for retesting of immunocompromised patients with prolonged COVID-19 symptoms and considering antiviral therapy.

Association of serum neurofilament light with microglial activation in multiple sclerosis.

BACKGROUND: Translocator protein (TSPO)-PET and neurofilament light (NfL) both report on brain pathology, but their potential association has not yet been studied in multiple sclerosis (MS) in vivo. We aimed to evaluate the association between serum NfL (sNfL) and TSPO-PET-measurable microglial activation in the brain of patients with MS. METHODS: Microglial activation was detected using PET and the TSPO-binding radioligand [11C]PK11195. Distribution volume ratio (DVR) was used to evaluate specific [11C]PK11195-binding. sNfL levels were measured using single molecule array (Simoa). The associations between [11C]PK11195 DVR and sNfL were evaluated using correlation analyses and false discovery rate (FDR) corrected linear regression modelling. RESULTS: 44 patients with MS (40 relapsing-remitting and 4 secondary progressive) and 24 age-matched and sex-matched healthy controls were included. In the patient group with elevated brain [11C]PK11195 DVR (n=19), increased sNfL associated with higher DVR in the lesion rim (estimate (95% CI) 0.49 (0.15 to 0.83), p(FDR)=0.04) and perilesional normal appearing white matter (0.48 (0.14 to 0.83), p(FDR)=0.04), and with a higher number and larger volume of TSPO-PET-detectable rim-active lesions defined by microglial activation at the plaque edge (0.46 (0.10 to 0.81), p(FDR)=0.04 and 0.50 (0.17 to 0.84), p(FDR)=0.04, respectively). Based on the multivariate stepwise linear regression model, the volume of rim-active lesions was the most relevant factor affecting sNfL. CONCLUSIONS: Our demonstration of an association between microglial activation as measured by increased TSPO-PET signal, and elevated sNfL emphasises the significance of smouldering inflammation for progression-promoting pathology in MS and highlights the role of rim-active lesions in promoting neuroaxonal damage.

Longitudinal stability of progression-related microglial activity during teriflunomide treatment in patients with multiple sclerosis.

BACKGROUND AND PURPOSE: The aim was to study brain innate immune cell activation in teriflunomide-treated patients with relapsing-remitting multiple sclerosis. METHODS: Imaging with 18-kDa translocator protein positron emission tomography (TSPO-PET) using the [11 C]PK11195 radioligand was employed to assess microglial activity in the white matter, thalamus and areas surrounding chronic white matter lesions in 12 patients with relapsing-remitting multiple sclerosis who had been treated with teriflunomide for at least 6 months before inclusion. Magnetic resonance imaging (MRI) was used to measure lesion load and brain volume, and quantitative susceptibility mapping (QSM) was used to detect iron rim lesions. These evaluations were repeated after 1 year of inclusion. Twelve age- and gender-matched healthy control subjects were imaged for comparison. RESULTS: Half of the patients had iron rim lesions. In TSPO-PET, the proportion of active voxels indicating innate immune cell activation was slightly greater amongst patients compared with healthy individuals (7.7% vs. 5.4%, p = 0.033). The mean distribution volume ratio of [11 C]PK11195 was not significantly different in the normal-appearing white matter or thalamus amongst patients versus controls. Amongst the treated patients, no significant alteration was observed in positron emission tomography distribution volume ratio, the proportion of active voxels, the number of iron-rim-positive lesions, lesion load or brain volume during follow-up. CONCLUSIONS: Compared to controls, treated patients exhibited modest signs of diffuse innate immune cell activity, which was unaltered during follow-up. Lesion-associated smoldering inflammation was negligible at both timepoints. To our knowledge, this is the first study applying both TSPO-PET and QSM-MRI to longitudinally evaluate smoldering inflammation.

Whole Brain Adiabatic T1rho and Relaxation Along a Fictitious Field Imaging in Healthy Volunteers and Patients With Multiple Sclerosis: Initial Findings.

BACKGROUND: In preclinical models of multiple sclerosis (MS), both adiabatic T1rho (T1ρadiab ) and relaxation along a fictitious field (RAFF) imaging have demonstrated potential to noninvasively characterize MS. PURPOSE: To evaluate the feasibility of whole brain T1ρadiab and RAFF imaging in healthy volunteers and patients with MS. STUDY TYPE: Single institutional clinical trial. SUBJECTS: 38 healthy volunteers (24-69 years) and 21 patients (26-59 years) with MS. Five healthy volunteers underwent a second MR examination performed within 8 days. Clinical disease severity (The Expanded Disability Status Scale [EDSS] and The Multiple Sclerosis Severity Score [MSSS]) was evaluated at baseline and 1-year follow-up (FU). FIELD STRENGTH/SEQUENCE: RAFF in second rotating frame of reference (RAFF2) was performed at 3 T using 3D-fast-field echo with magnetization preparation, RF amplitude of 11.74 µT while the corresponding value for T1ρadiab was 13.50 µT. T1 -, T2 -, and FLAIR-weighted images were acquired with reconstruction voxel size 1.0 × 1.0 × 1.0 mm3 . ASSESSMENT: The parametric maps of T1ρadiab and RAFF2 (TRAFF2 ) were calculated using a monoexponential model. Semi-automatic segmentation of MS lesions, white matter (WM), and gray matter (GM), and WM tracks was performed using T1 -, T2 -, and FLAIR-weighted images. STATISTICAL TESTS: Regression analysis was used to evaluate correlation of T1ρadiab and TRAFF2 with age and disease severity while a Friedman test followed by Wilcoxon Signed Rank test for differences between tissue types. Short-term repeatability was evaluated on voxel level. RESULTS: Both T1ρadiab and TRAFF2 demonstrated good short-term repeatability with relative differences on voxel level in the range of 6.1%-11.9%. Differences in T1ρadiab and TRAFF2 between the tissue types in MS patients were significant (P < 0.05). T1ρadiab and TRAFF2 correlated (P < 0.001) with baseline EDSS/MSSM and disease progression at FU (P < 0.001). DATA CONCLUSION: Whole brain T1ρadiab and TRAFF2 at 3 T was feasible with significant differences in T1ρadiab and TRAFF2 values between tissues types and correlation with disease severity. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 1.

Brain TSPO-PET predicts later disease progression independent of relapses in multiple sclerosis.

Overactivation of microglia is associated with most neurodegenerative diseases. In this study we examined whether PET-measurable innate immune cell activation predicts multiple sclerosis disease progression. Activation of microglia/macrophages was measured using the 18-kDa translocator protein (TSPO)-binding radioligand 11C-PK11195 and PET imaging in 69 patients with multiple sclerosis and 18 age- and sex-matched healthy controls. Radioligand binding was evaluated as the distribution volume ratio from dynamic PET images. Conventional MRI and disability measurements using the Expanded Disability Status Scale were performed for patients at baseline and 4.1 ± 1.9 (mean ± standard deviation) years later. Fifty-one (74%) of the patients were free of relapses during the follow-up period. Patients had increased activation of innate immune cells in the normal-appearing white matter and in the thalamus compared to the healthy control group (P = 0.033 and P = 0.003, respectively, Wilcoxon). Forward-type stepwise logistic regression was used to assess the best variables predicting disease progression. Baseline innate immune cell activation in the normal-appearing white matter was a significant predictor of later progression when the entire multiple sclerosis cohort was assessed [odds ratio (OR) = 4.26; P = 0.048]. In the patient subgroup free of relapses there was an association between macrophage/microglia activation in the perilesional normal-appearing white matter and disease progression (OR = 4.57; P = 0.013). None of the conventional MRI parameters measured at baseline associated with later progression. Our results strongly suggest that innate immune cell activation contributes to the diffuse neural damage leading to multiple sclerosis disease progression independent of relapses.

Effects of age, BMI and sex on the glial cell marker TSPO - a multicentre [11C]PBR28 HRRT PET study.

PURPOSE: The purpose of this study was to investigate the effects of ageing, sex and body mass index (BMI) on translocator protein (TSPO) availability in healthy subjects using positron emission tomography (PET) and the radioligand [11C]PBR28. METHODS: [11C]PBR28 data from 140 healthy volunteers (72 males and 68 females; N = 78 with HAB and N = 62 MAB genotype; age range 19-80 years; BMI range 17.6-36.9) were acquired with High Resolution Research Tomograph at three centres: Karolinska Institutet (N = 53), Turku PET centre (N = 62) and Yale University PET Center (N = 25). The total volume of distribution (VT) was estimated in global grey matter, frontal, temporal, occipital and parietal cortices, hippocampus and thalamus using multilinear analysis 1. The effects of age, BMI and sex on TSPO availability were investigated using linear mixed effects model, with TSPO genotype and PET centre specified as random intercepts. RESULTS: There were significant positive correlations between age and VT in the frontal and temporal cortex. BMI showed a significant negative correlation with VT in all regions. Additionally, significant differences between males and females were observed in all regions, with females showing higher VT. A subgroup analysis revealed a positive correlation between VT and age in all regions in male subjects, whereas age showed no effect on TSPO levels in female subjects. CONCLUSION: These findings provide evidence that individual biological properties may contribute significantly to the high variation shown in TSPO binding estimates, and suggest that age, BMI and sex can be confounding factors in clinical studies.

PET-measurable innate immune cell activation reduction in chronic active lesions in PPMS brain after rituximab treatment: a case report.

OBJECTIVES: To evaluate the effects of rituximab treatment on innate immune cell activation in primary progressive multiple sclerosis (PPMS). METHODS: A 48-year-old woman with PPMS was started on rituximab shortly after diagnosis. [11C]PK11195 PET imaging was employed to assess innate immune cell activation with special interest in the white matter around chronic lesions. PET, MRI, and disability measurements were performed at baseline and after 18 months of rituximab treatment. Specific binding of [11C]PK11195 was quantified using mean distribution volume ratios (DVRs), and at voxel-level based on proportions of active voxels. RESULTS: The PPMS patient had higher PK11195 DVRs and higher proportions of active voxels in the thalamus and the normal appearing white matter compared to the healthy control group. The thalamic and perilesional white matter DVRs and the proportions of active voxels decreased after rituximab treatment. The patient remained clinically stable during the 5-years follow-up. CONCLUSIONS: This case suggests that while a degree of smoldering activity persists, high efficacy B-cell-targeting therapy may contribute to reduced innate immune cell activation in PPMS brain areas relevant for disease progression. This case supports the therapeutic concept that controlling smoldering brain inflammation is beneficial for slowing down progression independent of relapses.

TSPO-Detectable Chronic Active Lesions Predict Disease Progression in Multiple Sclerosis.

BACKGROUND AND OBJECTIVES: In the multiple sclerosis (MS) brain, chronic active lesions can be detected using MRI- and PET-based methods. In this study, we investigated whether the frequency of TSPO-PET-detectable chronic active lesions associates with disease progression measured using the Expanded Disability Status Scale (EDSS) at 5-year follow-up. METHODS: Chronic lesion-associated innate immune cell activation was evaluated using TSPO-PET in 82 patients with MS. Chronic lesions were categorized into rim-active, inactive, and overall active lesion subtypes based on innate immune cell activation patterns in the lesion core and at the 2-mm perilesional rim. Logistic regression was used to identify best predictors of progression. RESULTS: Twenty-one patients experienced disability progression during the follow-up. These patients had a significantly higher proportion of rim-active lesions (p < 0.001) and a significantly lower proportion of inactive lesions (p = 0.001) compared with nonprogressed patients. The results were similar in the patient group having no relapses during the follow-up (60 patients, 14 experienced progression). In logistic regression modeling, the categorized variable "patients with >10% rim-active lesions and ≤50% inactive lesions of all chronic lesions" predicted disease progression in the entire cohort (OR = 26.8, p < 0.001) and in the group free of relapses (OR = 34.8, p = 0.002). DISCUSSION: The results show that single TSPO-PET-based in vivo lesion phenotyping of chronic MS lesions provides a strong predictor for MS disease progression. This emphasizes the significance of chronic active lesions in disability accumulation in MS.

Phenotyping of multiple sclerosis lesions according to innate immune cell activation using 18 kDa translocator protein-PET.

Chronic active lesions are promotors of neurodegeneration and disease progression in multiple sclerosis. They harbour a dense rim of activated innate immune cells at the lesion edge, which promotes lesion growth and thereby induces damage. Conventional MRI is of limited help in identifying the chronic active lesions, so alternative imaging modalities are needed. Objectives were to develop a PET-based automated analysis method for phenotyping of chronic lesions based on lesion-associated innate immune cell activation and to comprehensively evaluate the prevalence of these lesions in the various clinical subtypes of multiple sclerosis, and their association with disability. In this work, we use 18 kDa translocator protein-PET imaging for phenotyping chronic multiple sclerosis lesions at a large scale. For this, we identified 1510 white matter T1-hypointense lesions from 91 multiple sclerosis patients (67 relapsing-remitting patients and 24 secondary progressive patients). Innate immune cell activation at the lesion rim was measured using PET imaging and the 18 kDa translocator protein-binding radioligand 11C-PK11195. A T1-hypointense lesion was classified as rim-active if the distribution volume ratio of 11C-PK11195-binding was low in the plaque core and considerably higher at the plaque edge. If no significant ligand binding was observed, the lesion was classified as inactive. Plaques that had considerable ligand binding both in the core and at the rim were classified as overall-active. Conventional MRI and disability assessment using the Expanded Disability Status Scale were performed at the time of PET imaging. In the secondary progressive cohort, an average of 19% (median, interquartile range: 11-26) of T1 lesions were rim-active in each individual patient, compared to 10% (interquartile range: 0-20) among relapsing-remitting patients (P = 0.009). Secondary progressive patients had a median of 3 (range: 0-11) rim-active lesions, versus 1 (range: 0-18) among relapsing-remitting patients (P = 0.029). Among those patients who had rim-active lesions (n = 63), the average number of active voxels at the rim was higher among secondary progressive compared to relapsing-remitting patients (median 158 versus 74; P = 0.022). The number of active voxels at the rim correlated significantly with the Expanded Disability Status Scale (R = 0.43, P < 0.001), and the volume of the rim-active lesions similarly correlated with the Expanded Disability Status Scale (R = 0.45, P < 0.001). Our study is the first to report in vivo phenotyping of chronic lesions at large scale, based on 18 kDa translocator protein-PET. Patients with higher disability displayed a higher proportion of rim-active lesions. The in vivo lesion phenotyping methodology offers a new tool for individual assessment of smouldering (rim-active) lesion burden.

Innate Immune Cell-Related Pathology in the Thalamus Signals a Risk for Disability Progression in Multiple Sclerosis.

BACKGROUND AND OBJECTIVES: Our aim was to investigate whether 18-kDa translocator protein (TSPO) radioligand binding in gray matter (GM) predicts later disability progression in multiple sclerosis (MS). METHODS: In this prospective imaging study, innate immune cells were investigated in the MS patient brain using PET imaging. The distribution volume ratio (DVR) of the TSPO-binding radioligand [11C]PK11195 was determined in 5 GM regions: thalamus, caudate, putamen, pallidum, and cortical GM. Volumetric brain MRI parameters were obtained for comparison. The Expanded Disability Status Scale (EDSS) score was assessed at baseline and after follow-up of 3.0 ± 0.3 (mean ± SD) years. Disability progression was defined as an EDSS score increase of 1.0 point or 0.5 point if the baseline EDSS score was ≥6.0. A forward-type stepwise logistic regression model was constructed to compare multiple imaging and clinical variables in their ability to predict later disability progression. RESULTS: The cohort consisted of 66 patients with MS and 18 healthy controls. Patients with later disability progression (n = 17) had more advanced atrophy in the thalamus, caudate, and putamen at baseline compared with patients with no subsequent worsening. TSPO binding was significantly higher in the thalamus among the patients with later worsening. The thalamic DVR was the only measured imaging variable that remained a significant predictor of disability progression in the regression model. The final model predicted disability progression with 52.9% sensitivity and 93.9% specificity with an area under the curve value of 0.82 (receiver operating characteristic curve). DISCUSSION: Increased TSPO radioligand binding in the thalamus has potential in predicting short-term disability progression in MS and seems to be more sensitive for this than GM atrophy measures.

Association between microglial activation and serum kynurenine pathway metabolites in multiple sclerosis patients.

BACKGROUND: Microglial activation associates with MS progression but it is unclear what drives their persistent pro-inflammatory state. Metabolites of the kynurenine pathway (KP), the main metabolism route of tryptophan, can influence the function of brain innate immune cells. OBJECTIVE: To investigate whether tryptophan metabolites in blood associate with TSPO-PET measurable microglial activation in MS brain. METHODS: Microglial activation was detected using PET imaging and the TSPO-binding radioligand [11C]PK11195. Distribution volume ratios (DVR) for specific [11C]PK11195-binding in the normal appearing white matter (NAWM), lesions, and thalamus were calculated. Ultrahigh performance liquid chromatography-tandem mass spectrometry was used to measure serum levels of tryptophan and kynurenine pathway metabolites. RESULTS: The study cohort consisted of 48 MS patients. Increased DVR in the NAWM and thalamus correlated with decreased serum 3-hydroxykynurenine level (R = -0.31, p = 0.031 and R = -0.32, p = 0.028). Increased EDSS correlated with decreased 3-hydroxykynurenine and xanthurenic acid (R = -0.36, p = 0.012 and R = -0.31, p = 0.034) and increased DVR in the NAWM and thalamus (R = 0.33, p = 0.023 and R = 0.34, p = 0.020, respectively). CONCLUSIONS: This clinical study demonstrates an association between low serum 3-hydroxykynurenine and high microglial activation in MS. Further investigations are warranted for elucidation of the biological mechanisms behind this association.

Increased serum glial fibrillary acidic protein associates with microstructural white matter damage in multiple sclerosis: GFAP and DTI.

BACKGROUND: Astrocytes and microglial cells are now recognized as active players in contributing to the diffuse neuroaxonal damage associated with disease progression of multiple sclerosis (MS). The serum level of glial fibrillary acidic protein (GFAP), a biomarker for astrocytic activation, is increased in MS and associates with disease progression and disability. Similarly, diffusion tensor imaging (DTI) parameters for microstructural changes in brain, including demyelination and axonal loss, associate with disability. The association between brain DTI parameters and serum GFAP has not been previously explored in MS. The objective of the study was to get insights into DTI-measurable pathological correlates of elevated serum GFAP in the normal appearing white matter (NAWM) of MS. METHODS: A total of 62 MS patients with median age of 49.2 years were included in the study. Study patients underwent DTI-MRI and blood sampling for GFAP determination by single molecule array (Simoa). Mean fractional anisotropy (FA) and mean (MD), axial (AD) and radial (RD) diffusivities were calculated within the entire NAWM and six segmented NAWM regions. The associations between the DTI parameters and GFAP levels were analysed using Spearman correlation analysis and multiple regression model with sex and disease modifying treatment (no, 1st line or 2nd line) as adjustments. RESULTS: Elevated serum GFAP levels correlated significantly with decreased FA values within the entire (ρ = -0.39, p = 0.03), frontal (ρ = -0.42, p = 0.02), temporal (ρ = -0.37; p = 0.04) and cingulate (ρ = -0.38, p = 0.034) NAWM, and increased MD and RD within the frontal NAWM (ρ = 0.36, p = 0.046 for both). Similarly, higher GFAP associated with lower FA in frontal and cingulate NAWM in the multiple regression model corrected for confounding variables (standardised regression coefficient ß = -0.29, p = 0.045 and ß = -0.33, p = 0.025). CONCLUSIONS: Our results give evidence that increased serum GFAP levels associate with DTI-measurable micro-damage in the NAWM in MS. Our work supports the use of serum GFAP as a biomarker for MS pathology-related astrocytopathy and related diffuse white matter damage.

Fingolimod treatment reverses signs of diffuse white matter damage in multiple sclerosis: A pilot study.

BACKGROUND: In multiple sclerosis (MS) diffuse normal appearing white matter (NAWM) damage may drive chronic worsening independent of relapse activity. Diffusion tensor imaging (DTI) is a nonconventional MRI technique that can be used to assess microstructural alterations in myelin and axons. The aim of our study was to investigate the effect of six months fingolimod treatment on the integrity of entire and segmented NAWM in patients with relapsing-remitting multiple sclerosis (RRMS). METHODS: Ten RRMS patients initiating fingolimod treatment were included in the study. Patients underwent 3 T MRI including diffusion tensor sequences at baseline before the initiation of treatment and at six months. The mean values for fractional anisotropy (FA), and mean, radial and axial diffusivities (MD, RD and AD) were calculated within the whole NAWM and in six segmented sub-regions of NAWM (frontal, parietal, temporal, occipital, cingulate and deep NAWM). Clinical characteristics, Expanded Disability Status Scale (EDSS) and volumetric MRI data were also evaluated. RESULTS: In the cingulate NAWM FA was increased and RD was decreased significantly at six months compared to baseline (0.462 vs. 0.472, P = 0.027 and 0.000646 vs. 0.000634, P = 0.041, respectively), indicating improvements in myelin and axonal integrity following fingolimod treatment, whereas there were no alterations in cingulate MD or AD. Cingulate and temporal FA and RD correlated with T2 lesion volume percentage of cingulate and temporal areas. EDSS change correlated with change of the whole NAWM AD. CONCLUSIONS: Increased FA and decreased RD in the cingulate NAWM might suggest microstructural fingolimod-induced improvements in the normal appearing cingulate white matter. Our results support the concept that DTI can be used as a marker of diffuse neuronal damage also in interventional settings.

High serum neurofilament associates with diffuse white matter damage in MS.

OBJECTIVE: To evaluate to which extent serum neurofilament light chain (NfL) increase is related to diffusion tensor imaging-MRI measurable diffuse normal-appearing white matter (NAWM) damage in MS. METHODS: Seventy-nine patients with MS and 10 healthy controls underwent MRI including diffusion tensor sequences and serum NfL determination by single molecule array (Simoa). Fractional anisotropy and mean, axial, and radial diffusivities were calculated within the whole and segmented (frontal, parietal, temporal, occipital, cingulate, and deep) NAWM. Spearman correlations and multiple regression models were used to assess the associations between diffusion tensor imaging, volumetric MRI data, and NfL. RESULTS: Elevated NfL correlated with decreased fractional anisotropy and increased mean, axial, and radial diffusivities in the entire and segmented NAWM (for entire NAWM ρ = -0.49, p = 0.005; ρ = 0.49, p = 0.005; ρ = 0.43, p = 0.018; and ρ = 0.48, p = 0.006, respectively). A multiple regression model examining the effect of diffusion tensor indices on NfL showed significant associations when adjusted for sex, age, disease type, the expanded disability status scale, treatment, and presence of relapses. In the same model, T2 lesion volume was similarly associated with NfL. CONCLUSIONS: Our findings suggest that elevated serum NfL in MS results from neuroaxonal damage both within the NAWM and focal T2 lesions. This pathologic heterogeneity ought to be taken into account when interpreting NfL findings at the individual patient level.

Rituximab in the treatment of multiple sclerosis in the Hospital District of Southwest Finland.

BACKGROUND: There are already numerous B-cell depleting monoclonal anti-CD20 antibodies which have been used to reduce the inflammatory burden associated with multiple sclerosis (MS). We describe here our experience of treating MS-patients with B-cell depleting rituximab. PATIENTS AND METHODS: All MS-patients (n = 72) who had received rituximab treatment for at least six months by January 2019 were identified from the patient charts at the Turku University Hospital. Information about MS disease subtype, disease severity, MR-imaging outcomes and B-cell counts were collected from the charts. RESULTS: Rituximab was well received and well tolerated by the patients. There were no serious infusion-related side effects. The most serious adverse event that led to treatment discontinuation was neutropenia. After rituximab initiation the annual number of relapses was decreased in the relapsing remitting and secondary progressive MS groups and the mean number of gadolinium-enhancing lesions was decreased in relapsing remitting MS. Our study confirms the usability of rituximab treatment for MS in the Finnish health care environment. CONCLUSIONS: Off-label rituximab-treatment can be successfully used to reduce MS disease burden for the benefit of MS patients.

Insights into disseminated MS brain pathology with multimodal diffusion tensor and PET imaging.

OBJECTIVE: To evaluate in vivo the co-occurrence of microglial activation and microstructural white matter (WM) damage in the MS brain and to examine their association with clinical disability. METHODS: 18-kDa translocator protein (TSPO) brain PET imaging was performed for evaluation of microglial activation by using the radioligand [11C](R)-PK11195. TSPO binding was evaluated as the distribution volume ratio (DVR) from dynamic PET images. Diffusion tensor imaging (DTI) and conventional MRI (cMRI) were performed at the same time. Mean fractional anisotropy (FA) and mean (MD), axial, and radial (RD) diffusivities were calculated within the whole normal-appearing WM (NAWM) and segmented NAWM regions appearing normal in cMRI. Fifty-five patients with MS and 15 healthy controls (HCs) were examined. RESULTS: Microstructural damage was observed in the NAWM of the MS brain. DTI parameters of patients with MS were significantly altered in the NAWM compared with an age- and sex-matched HC group: mean FA was decreased, and MD and RD were increased. These structural abnormalities correlated with increased TSPO binding in the whole NAWM and in the temporal NAWM (p < 0.05 for all correlations; p < 0.01 for RD in the temporal NAWM). Both compromised WM integrity and increased microglial activation in the NAWM correlated significantly with higher clinical disability measured with the Expanded Disability Status Scale score. CONCLUSIONS: Widespread structural disruption in the NAWM is linked to neuroinflammation, and both phenomena associate with clinical disability. Multimodal PET and DTI allow in vivo evaluation of widespread MS pathology not visible using cMRI.

Natalizumab treatment reduces microglial activation in the white matter of the MS brain.

Objective: To evaluate whether natalizumab treatment reduces microglial activation in MS. Methods: We measured microglial activation using the 18-kDa translocator protein (TSPO)-binding radioligand [11C]PK11195 and PET imaging in 10 patients with MS before and after 1 year treatment with natalizumab. Microglial activation was evaluated as the distribution volume ratio (DVR) of the specifically bound radioligand in brain white and gray matter regions of interest. MRI and disability measurements were performed for comparison. Evaluation was performed identically with 11 age- and sex-matched patients with MS who had no MS therapy. Results: Natalizumab treatment reduced microglial activation in the normal-appearing white matter (NAWM; baseline DVR vs DVR after 1 year of treatment 1.25 vs 1.22, p = 0.014, Wilcoxon) and at the rim of chronic lesions (baseline DVR vs DVR after 1 year of treatment 1.24 vs 1.18, p = 0.014). In patients with MS with no treatment, there was an increase in microglial activation at the rim of chronic lesions (1.23 vs 1.27, p = 0.045). No alteration was observed in microglial activation in gray matter areas. In the untreated patient group, higher microglial activation at baseline was associated with more rapid disability progression during an average of 4 years of follow-up. Conclusions: TSPO-PET imaging can be used as a tool to assess longitudinal changes in microglial activation in the NAWM and in the perilesional areas in the MS brain in vivo. Natalizumab treatment reduces the diffuse compartmentalized CNS inflammation related to brain resident innate immune cells.

Microglial activation, white matter tract damage, and disability in MS.

OBJECTIVE: To investigate the relationship of in vivo microglial activation to clinical and MRI parameters in MS. METHODS: Patients with secondary progressive MS (n = 10) or relapsing-remitting MS (n = 10) and age-matched healthy controls (n = 17) were studied. Microglial activation was measured using PET and radioligand [11C](R)-PK11195. Clinical assessment and structural and quantitative MRI including diffusion tensor imaging (DTI) were performed for comparison. RESULTS: [11C](R)-PK11195 binding was significantly higher in the normal-appearing white matter (NAWM) of patients with secondary progressive vs relapsing MS and healthy controls, in the thalami of patients with secondary progressive MS vs controls, and in the perilesional area among the progressive compared with relapsing patients. Higher binding in the NAWM was associated with higher clinical disability and reduced white matter (WM) structural integrity, as shown by lower fractional anisotropy, higher mean diffusivity, and increased WM lesion load. Increasing age contributed to higher microglial activation in the NAWM among patients with MS but not in healthy controls. CONCLUSIONS: PET can be used to quantitate microglial activation, which associates with MS progression. This study demonstrates that increased microglial activity in the NAWM correlates closely with impaired WM structural integrity and thus offers one rational pathologic correlate to diffusion tensor imaging (DTI) parameters.

Evaluation of the Effect of Fingolimod Treatment on Microglial Activation Using Serial PET Imaging in Multiple Sclerosis.

Traditionally, multiple sclerosis (MS) has been considered a white matter disease with focal inflammatory lesions. It is, however, becoming clear that significant pathology, such as microglial activation, also takes place outside the plaque areas, that is, in areas of normal-appearing white matter (NAWM) and gray matter (GM). Microglial activation can be detected in vivo using 18-kDa translocator protein (TSPO)-binding radioligands and PET. It is unknown whether fingolimod affects microglial activation in MS. The aim of this study was to investigate whether serial PET can be used to evaluate the effect of fingolimod treatment on microglial activation. Methods: Ten relapsing-remitting MS patients were studied using the TSPO radioligand 11C-(R)-PK11195. Imaging was performed at baseline and after 8 and 24 wk of fingolimod treatment. Eight healthy individuals were imaged for comparison. Microglial activation was evaluated as distribution volume ratio of 11C-(R)-PK11195. Results: The patients had MS for an average of 7.9 ± 4.3 y (mean ± SD), their total relapses averaged 4 ± 2.4, and their Expanded Disability Status Scale was 2.7 ± 0.5. The patients were switched to fingolimod because of safety reasons or therapy escalation. The mean washout period before the initiation of fingolimod was 2.3 ± 1.1 mo. The patients were clinically stable on fingolimod. At baseline, microglial activation was significantly higher in the combined NAWM and GM areas of MS patients than in healthy controls (P = 0.021). 11C-(R)-PK11195 binding was reduced (-12.31%) within the combined T2 lesion area after 6 mo of fingolimod treatment (P = 0.040) but not in the areas of NAWM or GM. Conclusion: Fingolimod treatment reduced microglial/macrophage activation at the site of focal inflammatory lesions, presumably by preventing leukocyte trafficking from the periphery. It did not affect the widespread, diffuse microglial activation in the NAWM and GM. The study opens new vistas for designing future therapeutic studies in MS that use the evaluation of microglial activation as an imaging outcome measure.