Disruption of Rich-Club Connectivity in Cushing Disease

Analysis of brain structural covariance network in Cushing disease

BACKGROUND

Cushing disease (CD) is a rare clinical neuroendocrine disease. CD is characterized by abnormal hypercortisolism induced by a pituitary adenoma with the secretion of adrenocorticotropic hormone. Individuals with CD usually exhibit atrophy of gray matter volume. However, little is known about the alterations in topographical organization of individuals with CD. This study aimed to investigate the structural covariance networks of individuals with CD based on the gray matter volume using graph theory analysis.

METHODS

High-resolution T1-weighted images of 61 individuals with CD and 53 healthy controls were obtained. Gray matter volume was estimated and the structural covariance network was analyzed using graph theory. Network properties such as hubs of all participants were calculated based on degree centrality.

RESULTS

No significant differences were observed between individuals with CD and healthy controls in terms of age, gender, and education level. The small-world features were conserved in individuals with CD but were higher than those in healthy controls. The individuals with CD showed higher global efficiency and modularity, suggesting higher integration and segregation as compared to healthy controls. The hub nodes of the individuals with CD were Short insular gyri (G_insular_short_L), Anterior part of the cingulate gyrus and sulcus (G_and_S_cingul-Ant_R), and Superior frontal gyrus (G_front_sup_R).

CONCLUSIONS

Significant differences in the structural covariance network of patients with CD were found based on graph theory. These findings might help understanding the pathogenesis of individuals with CD and provide insight into the pathogenesis of this CD.

Irreversible Alterations of Susceptibility in Cushing's Disease: A Longitudinal QSM Study

OBJECTIVES

Chronic exposure to hypercortisolism is associated with accelerated aging and neurodegenerative diseases, while Cushing's disease (CD) is the most common form of endogenous hypercortisolism exposure. This study aimed to assess longitudinal susceptibility changes in CD using quantitative susceptibility mapping (QSM) before and after resolution of hypercortisolism.

METHODS

In this study, 24 CD patients and 24 healthy controls underwent magnetic resonance imaging (MRI) with QSM. All CD patients underwent MRI scans before and after the curative operation.

RESULTS

After resolution of hypercortisolism, irreversibly altered susceptibility values were found in the anterior cingulate cortex, frontal lobe, caudate, and red nucleus. These alterations were significantly correlated with the changes in gray matter/white matter volumes and clinical features. Additionally, decreased susceptibility was found in several regions in CD patients.

CONCLUSION

Chronic exposure to hypercortisolism may be related to susceptibility alterations and significantly correlated with altered brain volumes and clinical features. in CD patients. The decrease of susceptibility might suggest the involvement of the calcium deregulation in these alterations.

Functional brain alterations in Cushing's syndrome

Cognitive impairment and affective disorders are common in patients with Cushing's syndrome (CS). In fact, as an effect of prolonged cortisol excess on the brain, patients with CS often have memory problems, concentration difficulties, impaired attention and executive function, that are not always reversible following successful treatment. Neuroimaging is essential for understanding the deleterious effects of hypercortisolism on the brain. In CS, structural alterations have been observed, including reduction of hippocampal volume, amygdala and the prefrontal cortex. The aim of this article is to summarize results from studies that have used functional magnetic resonance imaging (fMRI) to study functional brain alterations in patients with CS. In these studies, alterations in brain areas and networks essential for cognitive function, emotional processing, and executive function have been observed, both in patients with active CS as well as following treatment. Nevertheless, longitudinal studies with a comprehensive evaluation of functional brain alterations and neurocognitive evaluation are still needed to determine whether the apparent deleterious effects of hypercortisolism on the brain are reversible or not.

Structural and functional brain alterations in Cushing's disease: A narrative review

Neurocognitive and psychiatric symptoms are non-negligible in Cushing's disease and are accompanied by structural and functional alterations of the brain. In this review, we have summarized multimodal neuroimaging and neurophysiological studies to highlight the current and historical understandings of the structural and functional brain alterations in Cushing's disease. Specifically, structural studies showed atrophy of the gray matter, loss of white matter integrity, and demyelination in widespread brain regions. Functional imaging studies have identified three major functional brain connectome networks influenced by hypercortisolemia: the limbic network, the default mode network, and the executive control network. After endocrinological remission, atrophy of gray matter regions and the compromised functional network activities were partially reversible, and the widespread white matter integrity alterations cannot recover in years. In conclusion, Cushing's disease patients display structural and functional brain connectomic alterations, which provides insights into the neurocognitive and psychiatric symptoms observed in this disease.

Diffusion spectrum imaging of patients with middle cerebral artery stenosis

OBJECTIVE

We aimed to detect microstructural changes in the brains of patients with unilateral middle cerebral artery (MCA) stenosis and to assess the integrity of the fiber structure and the small-world networks using diffusion spectrum imaging (DSI).

METHODS

A total of 21 healthy controls and 48 patients with unilateral MCA stenosis underwent 3.0 T MRI examination using DSI technique. Differential tractography, diffusion connectometry, and structural networks were performed by using DSI software. The correlation between the stenosis and quantitative anisotropy (QA) were analyzed using multiple regression models in the correlation tractography.

RESULTS

Differential tractography analysis showed that the left or right MCA stenosis group had decreased fiber connectivity in the brain network compared with the control group. The correlation tractography analysis of the patients with MCA stenosis showed that QA was negatively correlated with stenosis in the bilateral arcuate fasciculus, bilateral corticostriatal and corticothalamic pathway, bilateral corticopontine and corticospinal tract, right superior longitudinal fasciculus, right cingulum, corpus callosum, and left frontal aslant tract. Statistically significant differences were shown between the MCA stenosis groups and control group in graph density, global efficiency, network path length, and rich club coefficient.

CONCLUSION

DSI revealed that stroke-free patients with unilateral MCA stenosis have a disrupted structural network and damaged white matter fibers. Furthermore, the fiber connection disruption is more severe in the ipsilateral hemisphere and less prominent in the contralateral hemisphere in patients with unilateral MCA stenosis. Therefore, microstructural impairment has happened to patients with unilateral MCA stenosis even at a subclinical stage.

Long-term effects of glucocorticoid excess on the brain

The metabolic and cardiovascular clinical manifestations in patients with Cushing's syndrome (CS) are generally well known. However, recent studies have broadened the perspective of the effects of hypercortisolism, showing that both endogenous and exogenous glucocorticoid excess alter brain functioning on several time scales. Consequently, cognitive deficits and neuropsychological symptoms are highly prevalent during both active CS and CS in remission, as well as during glucocorticoid treatment. In this review, we discuss the effects of endogenous hypercortisolism and exogenously induced glucocorticoid excess on the brain, as well as the prevalence of cognitive and neuropsychological deficits and their course after biochemical remission. Furthermore, we propose possible mechanisms that may underly neuronal changes, based on experimental models and in vitro studies. Finally, we offer recommendations for future studies.