Anorexia nervosa and diffusion weighted imaging: An open methodological question raised by a systematic review and a fractional anisotropy anatomical likelihood estimation meta-analysis

Corpus callosum morphology and relationships to illness phenotypes in individuals with anorexia nervosa

Anorexia nervosa is an often-severe psychiatric illness characterized by significantly low body weight, fear of gaining weight, and distorted body image. Multiple neuroimaging studies have shown abnormalities in cortical morphology, mostly associated with the starvation state. Investigations of white matter, while more limited in number, have suggested global and regional volume reductions, as well as abnormal diffusivity in multiple regions including the corpus callosum. Yet, no study has specifically examined thickness of the corpus callosum, a large white matter tract instrumental in the inter-hemispheric integration of sensory, motor, and cognitive information. We analyzed MRI data from 48 adolescents and adults with anorexia nervosa and 50 healthy controls, all girls/women, to compare corpus callosum thickness and examined relationships with body mass index (BMI), illness duration, and eating disorder symptoms (controlling for BMI). There were no significant group differences in corpus callosum thickness. In the anorexia nervosa group, severity of body shape concerns was significantly, positively correlated with callosal thickness in the rostrum, genu, rostral body, isthmus, and splenium. In addition, there were significant positive correlations between eating disorder-related obsessions and compulsions and thickness of the anterior midbody, rostral body, and splenium. There were no significant associations between callosal thickness and BMI or illness duration. In sum, those with AN with worse concerns about bodily appearance and worse eating disorder-related obsessive thought patterns and compulsive behaviours have regionally thicker corpus callosum, independent of current weight status. These findings provide important neurobiological links to key, specific eating disorder behavioural phenotypes.

Intra-individual cortical networks in Anorexia Nervosa: Evidence from a longitudinal dataset

OBJECTIVE

This work investigates cortical thickness (CT) and gyrification patterns in Anorexia Nervosa (AN) before and after short-term weight restoration using graph theory tools.

METHODS

38 female adolescents with AN underwent structural magnetic resonance imaging scans at baseline and after - on average - 3.5 months following short-term weight restoration while 53 age-matched healthy controls (HCs) were scanned once. Graph measures were compared between groups and longitudinally within the AN group. Associations with clinical measures such as age of onset, duration of illness, BMI standard deviation score (BMI-SDS), and longitudinal weight changes were tested via stepwise regression.

RESULTS

Cortical thickness graphs of patients with acute AN displayed lower modularity and small-world index (SWI) than HCs. Modularity recovered after weight gain. Reduced global efficiency and SWI were observed in patients at baseline compared to HCs based on gyrification networks. Significant associations between local clustering of CT at admission and BMI-SDS, and clustering/global efficiency of gyrification and duration of illness emerged.

CONCLUSIONS

Our results indicate a shift towards less organised CT networks in patients with acute AN. After weight recovery, the disarrangement seems to be partially reduced. However, longer-term follow-ups are needed to determine whether cortical organizational patterns fully return to normal.

Machine learning research based on diffusion tensor images to distinguish between anorexia nervosa and bulimia nervosa

Background

Anorexia nervosa (AN) and bulimia nervosa (BN), two subtypes of eating disorders, often present diagnostic challenges due to their overlapping symptoms. Machine learning has proven its capacity to improve group classification without requiring researchers to specify variables. The study aimed to distinguish between AN and BN using machine learning models based on diffusion tensor images (DTI).

Methods

This is a cross-sectional study, drug-naive females diagnosed with anorexia nervosa (AN) and bulimia nervosa (BN) were included. Demographic data and DTI were collected for all patients. Features for machine learning included Fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD). Support vector machine was constructed by LIBSVM, MATLAB2013b, and FSL5.0.9 software.

Results

A total of 58 female patients (24 AN, 34 BN) were included in this study. Statistical analysis revealed no significant differences in age, years of education, or course of illness between the two groups. AN patients had significantly lower BMI than BN patients. The AD model exhibited an area under the curve was 0.793 (accuracy: 75.86%, sensitivity: 66.67%, specificity: 88.23%), highlighting the left middle temporal gyrus (MTG_L) and the left superior temporal gyrus (STG_L) as differentiating brain regions. AN patients exhibited lower AD features in the STG_L and MTG_L than BN. Machine learning analysis indicated no significant differences in FA, MD, and RD values between AN and BN groups (p > 0.001).

Conclusion

Machine learning based on DTI could effectively distinguish between AN and BN, with MTG_L and STG_L potentially serving as neuroimaging biomarkers.

Habits and Persistent Food Restriction in Patients with Anorexia Nervosa: A Scoping Review

The aetiology of anorexia nervosa (AN) presents a puzzle for researchers. Recent research has sought to understand the behavioural and neural mechanisms of these patients' persistent choice of calorie restriction. This scoping review aims to map the literature on the contribution of habit-based learning to food restriction in AN. PRISMA-ScR guidelines were adopted. The search strategy was applied to seven databases and to grey literature. A total of 35 studies were included in this review. The results indicate that the habit-based learning model has gained substantial attention in current research, employing neuroimaging methods, scales, and behavioural techniques. Food choices were strongly associated with dorsal striatum activity, and habitual food restriction based on the self-report restriction index was associated with clinical impairment in people chronically ill with restricting AN. High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) and Regulating Emotions and Changing Habits (REaCH) have emerged as potential treatments. Future research should employ longitudinal studies to investigate the time required for habit-based learning and analyse how developmental status, such as adolescence, influences the role of habits in the progression and severity of diet-related illnesses. Ultimately, seeking effective strategies to modify persistent dietary restrictions controlled by habits remains essential.

Investigation of brain iron in anorexia nervosa, a quantitative susceptibility mapping study

BACKGROUND

Anorexia nervosa (AN) is a potentially fatal psychiatric condition, associated with structural brain changes such as gray matter volume loss. The pathophysiological mechanisms for these changes are not yet fully understood. Iron is a crucial element in the development and function of the brain. Considering the systemic alterations in iron homeostasis in AN, we hypothesized that brain iron would be altered as a possible factor associated with structural brain changes in AN.

METHODS

In this study, we used quantitative susceptibility mapping (QSM) magnetic resonance imaging to investigate brain iron in current AN (c-AN) and weight-restored AN compared with healthy individuals. Whole-brain voxel wise comparison was used to probe areas with possible group differences. Further, the thalamus, caudate nucleus, putamen, nucleus accumbens, hippocampus, and amygdala were selected as the regions of interest (ROIs) for ROI-based comparison of mean QSM values.

RESULTS

Whole-brain voxel-wise and ROI-based comparison of QSM did not reveal any differences between groups. Exploratory analyses revealed a correlation between higher regional QSM (higher iron) and lower body mass index, higher illness severity, longer illness duration, and younger age at onset in the c-AN group.

CONCLUSIONS

This study did not find evidence of altered brain iron in AN compared to healthy individuals. However, the correlations between clinical variables and QSM suggest a link between brain iron and weight status or biological processes in AN, which warrants further investigation.

Attachment Trauma Is Associated with White Matter Fiber Microstructural Alterations in Adolescents with Anorexia Nervosa before and after Exposure to Psychotherapeutic and Nutritional Treatment

In the present study, we explore the role of attachment for microstructural white matter (WM) changes in adolescents with anorexia nervosa (AN) before and after exposure to short-term and nutritional treatment. The case sample consisted of 22 female adolescent inpatients with AN (mean age: 15.2 ± 1.2 years) and the control sample were 18 gender-matched healthy adolescents (mean age: 16.8 ± 0.9 years). We performed a 3T MRI in the patient group during the acute state of AN and after weight restoration (duration: 2.6 ± 1 months) and compared the data to a healthy control group. To classify attachment patterns, we used the Adult Attachment Projective Picture System. In the patient sample, over 50% were classified with an attachment trauma/unresolved attachment status. Prior to treatment exposure, fractional anisotropy (FA) reductions and concordant mean diffusivity (MD) increases were evident in the fornix, the corpus callosum and WM regions of the thalamus, which normalized in the corpus callosum and the fornix post-therapy in the total patient sample (p < 0.002). In the acute state, patients with an attachment trauma demonstrated significant FA decreases compared to healthy controls, but no MD increases, in the corpus callosum and cingulum bilaterally, which remained decreased after therapy. Attachment patterns seem to be associated with region-specific changes of WM alterations in AN.

Time evaluation and its accuracy in eating disorders: differences in relation to interoceptive awareness

PURPOSE

Time evaluation has been poorly studied in eating disorder (ED) patients despite its relationship with body awareness, which is a core psychopathological feature in EDs and is influenced by impulsivity, interoception, and working memory. This study aims to evaluate time estimation and its accuracy across the ED spectrum in connection with specific and general psychopathology.

METHODS

A group of 215 women was enrolled in a computerized task involving the estimation of 1-min intervals. Impulsivity and body awareness constructs (self-monitoring, depersonalization, interoceptive deficit) were evaluated and examined for significant correlations with time estimation and the accuracy of the measure.

RESULTS

Patients with EDs showed an impaired ability to estimate time, with an accuracy that positively correlated with compulsive self-monitoring (p = 0.03). Differences between diagnostic subgroups showed an overestimation of time in anorexia nervosa patients and an underestimation of time in binge eating disorder patients, whose time estimation was also less accurate.

CONCLUSION

The relationship between time estimation and compulsive self- monitoring might corroborate the presence of an imbalanced integration of information in patients with EDs that was not present in the community women included in the study. Time perception should be further evaluated in the ED field, and longitudinal changes due to psychopathological recovery or BMI changes should be examined.

LEVEL OF EVIDENCE

Level III: Evidence obtained from a well-designed cohort or case-control analytic study.

Impulsivity and eating disorders: The relationship between serum 25-hydroxyvitamin D and different impulsivity facets in a transdiagnostic sample

OBJECTIVES

Eating disorders (EDs) are severe psychiatric conditions characterised by malnutrition, dysfunctional behaviours, and hypovitaminosis D. In various psychiatric conditions, including EDs, preliminary evidence has correlated impulsivity to a low level of 25-hydroxyvitamin D [25(OH)D]. This study aims to reinforce this evidence by examining different facets, both behavioural and psychological, of the impulsivity construct in patients with ED.

METHODS

A sample of 119 women was evaluated with a validated questionnaire and computerised neuropsychological tasks: the UPPS-P impulsive behaviour scale, a go/no-go task, and the Balloon Analogue Risk Task (BART). A clinical evaluation for EDs and blood sample collection were also performed to assess specific psychopathology and determine the serum level of 25(OH)D.

RESULTS

Significant correlations were found between serum levels of 25(OH)D and BART scores (p = 0.012) and lack of perseverance (p = 0.034). Moreover, regression analyses showed that higher BART scores may be explained by hypovitaminosis D and higher levels of lack of perseverance in patients with EDs.

CONCLUSIONS

The specific aspect of impulsivity linked to goal strategy and behaviours may be explained in patients with EDs by hypovitaminosis D. A possible connection to the brain inflammatory system is also discussed, along with possible directions for future research.

Altered White Matter Connectivity in Young Acutely Underweight Patients With Anorexia Nervosa

OBJECTIVE

Reductions of gray matter volume and cortical thickness in anorexia nervosa (AN) are well documented. However, findings regarding the integrity of white matter (WM) as studied via diffusion weighted imaging (DWI) are remarkably heterogeneous, and WM connectivity has been examined only in small samples using a limited number of regions of interest. The present study investigated whole-brain WM connectivity for the first time in a large sample of acutely underweight patients with AN.

METHOD

DWI data from predominantly adolescent patients with acute AN (n = 96, mean age = 16.3 years) and age-matched healthy control participants (n = 96, mean age = 17.2 years) were analyzed. WM connectivity networks were generated from fiber-tractography-derived streamlines connecting 233 cortical/subcortical regions. To identify group differences, network-based statistic was used while taking head motion, WM, and ventricular volume into account.

RESULTS

Patients with AN were characterized by 6 WM subnetworks with abnormal architecture, as indicated by increased fractional anisotropy located primarily in parietal-occipital regions and accompanied by reduced radial diffusivity. Group differences based on number of streamlines reached only nominal significance.

CONCLUSION

Our study reveals pronounced alterations in the WM connectome in young patients with AN. In contrast to known reductions in gray matter in the acutely underweight state of AN, this pattern does not necessarily indicate a deterioration of the WM network. Future studies using advanced MRI sequences will have to clarify interrelations with axonal packing or myelination, and whether the changes should be considered a consequence of undernutrition or a vulnerability for developing or maintaining AN.

Brain networks in eating disorders: a systematic review of graph theory studies

PURPOSE

Recent evidence from neuroimaging research has shown that eating disorders (EDs) are characterized by alterations in interconnected neural systems, whose characteristics can be usefully described by connectomics tools. The present paper aimed to review the neuroimaging literature in EDs employing connectomic tools, and, specifically, graph theory analysis.

METHODS

A systematic review of the literature was conducted to identify studies employing graph theory analysis on patients with eating disorders published before the 22nd of June 2020.

RESULTS

Twelve studies were included in the systematic review. Ten of them address anorexia nervosa (AN) (AN = 199; acute AN = 85, weight recovered AN with acute diagnosis = 24; fully recovered AN = 90). The remaining two articles address patients with bulimia nervosa (BN) (BN = 48). Global and regional unbalance in segregation and integration properties were described in both disorders.

DISCUSSION

The literature concerning the use of connectomics tools in EDs evidenced the presence of alterations in the topological characteristics of brain networks at a global and at a regional level. Changes in local characteristics involve areas that have been demonstrated to be crucial in the neurobiology and pathophysiology of EDs. Regional imbalances in network properties seem to reflect on global patterns.

LEVEL OF EVIDENCE

Level I, systematic review.

Structural brain changes in severe and enduring anorexia nervosa: A multimodal magnetic resonance imaging study of gray matter volume, cortical thickness, and white matter integrity

Whole-brain T1-weighted imaging and diffusion tensor imaging was performed in 35 adult women with anorexia nervosa (AN) and 35 healthy controls. We conducted voxel-based group comparisons for gray matter volume (GMV), cortical thickness (CT), and fractional anisotropy (FA) values, using age and total intracranial volume as nuisance covariates. We then conducted the same group comparisons for these three measures, but this time also controlled for the following global pathological measures: total GMV, mean CT across the whole brain, and mean FA across the entire white matter skeleton. Compared with the healthy controls, AN patients had lower GMV and CT in widespread cortical regions, and smaller FA values in widespread white matter regions. After controlling for global parameters, almost all of the differences between the two groups disappeared, except for higher CT in the medial orbital gyrus and parietal operculum in the AN group. Structural brain changes in AN are likely to be composed of both global and region-specific changes. The former changes are likely to have a dominant impact, while the latter changes might in part explain the disease-specific pathophysiology of AN.

Shift Toward Randomness in Brain Networks of Patients With Anorexia Nervosa: The Role of Malnutrition

No study to date investigated structural white matter (WM) connectome characteristics in patients with anorexia nervosa (AN). Previous research in AN found evidence of imbalances in global and regional connectomic brain architecture and highlighted a role of malnutrition in determining structural brain changes. The aim of our study was to explore the characteristics of the WM network architecture in a sample of patients with AN. Thirty-six patients with AN and 36 healthy women underwent magnetic resonance imaging to obtain a high-resolution three-dimensional T1-weighted anatomical image and a diffusion tensor imaging scan. Probabilistic tractography data were extracted and analyzed in their network properties through graph theory tools. In comparison to healthy women, patients with AN showed lower global network segregation (normalized clustering: p = 0.029), an imbalance between global network integration and segregation (i.e., lower small-worldness: p = 0.031), and the loss of some of the most integrative and influential hubs. Both clustering and small-worldness correlated with the lowest lifetime body mass index. A significant relationship was found between the average regional loss of cortical volume and changes in network properties of brain nodes: the more the difference in the cortical volume of brain areas, the more the increase in the centrality of corresponding nodes in the whole brain, and the decrease in clustering and efficiency of the nodes of parietal cortex. Our findings showed an unbalanced connectome wiring in AN patients, which seems to be influenced by malnutrition and loss of cortical volume. The role of this rearrangement in the maintenance and prognosis of AN and its reversibility with clinical improvement needs to be established by future studies.

Neuroimaging Findings in Adolescents and Young Adults with Anorexia Nervosa: A Systematic Review

BACKGROUND

Anorexia nervosa (AN) is a serious, multifactorial mental disorder affecting predominantly young females. This systematic review examines neuroimaging findings in adolescents and young adults up to 24 years old, in order to explore alterations associated with disease pathophysiology.

METHODS

Eligible studies on structural and functional brain neuroimaging were sought systematically in PubMed, CENTRAL and EMBASE databases up to 5 October 2020.

RESULTS

Thirty-three studies were included, investigating a total of 587 patients with a current diagnosis of AN and 663 healthy controls (HC). Global and regional grey matter (GM) volume reduction as well as white matter (WM) microstructure alterations were detected. The mainly affected regions were the prefrontal, parietal and temporal cortex, hippocampus, amygdala, insula, thalamus and cerebellum as well as various WM tracts such as corona radiata and superior longitudinal fasciculus (SLF). Regarding functional imaging, alterations were pointed out in large-scale brain networks, such as default mode network (DMN), executive control network (ECN) and salience network (SN). Most findings appear to reverse after weight restoration. Specific limitations of neuroimaging studies in still developing individuals are also discussed.

CONCLUSIONS

Structural and functional alterations are present in the early course of the disease, most of them being partially or totally reversible. Nonetheless, neuroimaging findings have been open to many biological interpretations. Thus, more studies are needed to clarify their clinical significance.

Developmental stage-dependent relationships between ghrelin levels and hippocampal white matter connections in low-weight anorexia nervosa and atypical anorexia nervosa

INTRODUCTION

Disruptions in homeostatic and hedonic food motivation are proposed to underlie anorexia nervosa (AN) and atypical AN, restrictive eating disorders which commonly onset in puberty. Ghrelin, a neuroprotective hormone that drives hedonic eating is increased in AN and is expressed in the hippocampus. White matter (WM) undergoes significant change during puberty in regions involved in food motivation, particularly WM tracts connected with the hippocampus. The association between ghrelin and WM region of interest (ROI) with hippocampal connections in restrictive eating disorders, particularly in adolescence during key neurodevelopmental growth, is unknown.

METHODS

We evaluated fasting plasma ghrelin and WM microstructure (measured by free-water corrected fractional anisotropy (FA-t)) in WM ROIs with hippocampal connections - the fornix and the hippocampal portion of the cingulum - in 56 adolescent females (age range: 11.9 - 22.1 y; mean: 19.0 y) with low-weight eating disorders including AN and atypical AN (N = 36) and healthy controls (N = 20).

RESULTS

FA-t in the fornix or hippocampal portion of the fornix did not differ between groups. Ghrelin was higher in AN/atypical AN vs. HC and was positively correlated with puberty stage in the AN/atypical AN group, but not the HC group. The correlation between ghrelin and FA-t in the fornix was significantly different in females with AN/atypical AN compared to controls. In AN/atypical AN, pubertal stage moderated the relation between fasting plasma ghrelin and FA-t in the fornix: higher fasting ghrelin was associated with lower FA-t in the fornix in late-post-puberty, but was not associated with FA-t in the early to mid stages of puberty.

CONCLUSIONS

In post-pubertal females with low-weight AN/atypical AN, higher levels of ghrelin are associated with lower FA-t in the fornix. This relationship is not evident in the early to mid stages of puberty in AN/atypical AN or in HC, and may reflect a lack of possible neuroprotective effects of ghrelin in late-post puberty only. Understanding the effects of ghrelin on WM microstructure longitudinally and following recovery from AN/Atypical AN and how this differs across pubertal stages will be an important next step. These findings could ultimately inform treatment staging and aid in diagnosis and detection of AN/atypical AN.

Genetic and epigenetic findings in anorexia nervosa

Polygenic factors are relevant for the genetic predispositions to the eating disorder anorexia nervosa (AN). The most recent genome-wide association study (GWAS) for AN comprised almost 17,000 patients with AN and controls. A total of eight genome-wide significant polygenic loci associated with AN have been identified. Each single polygenic locus makes only a small contribution to the development of AN. Analyses across different traits successfully identified regions/genes for AN that had not been detected by analyses of the single traits. Functional studies of the genes derived by GWAS studies aim to improve the understanding of the biological mechanisms involved in eating disorders. Epigenetic studies have not yet successfully contributed to the understanding of AN.