Left hemispatial neglect with a splenial lesion

Altered structural and functional connectivity in Posterior Cortical Atrophy and Dementia with Lewy bodies

Posterior cortical atrophy (PCA) and dementia with Lewy bodies (DLB) show distinct atrophy and overlapping hypometabolism profiles, but it is unknown how disruptions in structural and functional connectivity compare between these disorders and whether breakdowns in connectivity relate to either atrophy or hypometabolism. Thirty amyloid-positive PCA patients, 24 amyloid-negative DLB patients and 30 amyloid-negative cognitively unimpaired (CU) healthy individuals were recruited at Mayo Clinic, Rochester, MN, and underwent a 3T head MRI, including structural MRI, resting state functional MRI (rsfMRI) and diffusion tensor imaging (DTI) sequences, as well as [18F] fluorodeoxyglucose (FDG) PET. We assessed functional connectivity within and between 12 brain networks using rsfMRI and the CONN functional connectivity toolbox and calculated regional DTI metrics using the Johns Hopkins atlas. Multivariate linear-regression models corrected for multiple comparisons and adjusted for age and sex compared DTI metrics and within-network and between-network functional connectivity across groups. Regional gray-matter volumes and FDG-PET standard uptake value ratios (SUVRs) were calculated and analyzed at the voxel-level using SPM12. We used univariate linear-regression models to investigate the relationship between connectivity measures, gray-matter volume, and FDG-PET SUVR. On DTI, PCA showed degeneration in occipito-parietal white matter, posterior thalamic radiations, splenium of the corpus collosum and sagittal stratum compared to DLB and CU, with greater degeneration in the temporal white matter and the fornix compared to CU. We observed no white-matter degeneration in DLB compared to CU. On rsfMRI, reduced within-network connectivity was present in dorsal and ventral default mode networks (DMN) and the dorsal-attention network in PCA compared to DLB and CU, with reduced within-network connectivity in the visual and sensorimotor networks compared to CU. DLB showed reduced connectivity in the cerebellar network compared to CU. Between-network analysis showed increased connectivity in both cerebellar-to-sensorimotor and cerebellar-to-dorsal attention network connectivity in PCA and DLB. PCA showed reduced anterior DMN-to-cerebellar and dorsal attention-to-sensorimotor connectivity, while DLB showed reduced posterior DMN-to-sensorimotor connectivity compared to CU. PCA showed reduced dorsal DMN-to-visual connectivity compared to DLB. The multimodal analysis revealed weak associations between functional connectivity and volume in PCA, and between functional connectivity and metabolism in DLB. These findings suggest that PCA and DLB have unique connectivity alterations, with PCA showing more widespread disruptions in both structural and functional connectivity; yet some overlap was observed with both disorders showing increased connectivity from the cerebellum.

Amantadine as a Potential Treatment for Marchiafava–Bignami Disease: Case Reports and a Possible Mechanism

Introduction

Several reports have described the use of amantadine for managing symptoms in Marchiafava–Bignami disease (MBD); however, amantadine's role for the treatment of MBD symptoms is unclear. Here, we describe 2 patients with MBD who were treated with amantadine and hypothesize a potential mechanism responsible for clinical benefit. Case 1. A 38-year-old woman with excessive wine drinking presented with agitation, impaired speech, and a minimally conscious state. MRI revealed lesions in the splenium and genu. After being diagnosed with MBD, she was treated with intravenous thiamine, multivitamins, and 100 mg of amantadine twice a day for 2 weeks. She recovered to near baseline after 3 weeks. Case 2. A 54-year-old woman with years of heavy alcohol use presented with sudden bradyphrenia, acalculia, disinhibited behavior, weakness, and urinary incontinence. MRI revealed a large anterior callosal lesion. Two years after initial recovery from MBD, she noted that consuming “energy drinks” resulted in a transient, near-complete resolution of her residual behavioral, fatigue, and language symptoms. 100 mg of amantadine twice a day was trialled. After noted improvement, a further escalation to 200 mgs 3 times a day resulted in significant improvement in language and behavioral symptoms.

Conclusion

Amantadine in addition to vitamins may be beneficial in the treatment of MBD. It is possible that the dopaminergic effect of amantadine leads to improved recovery and function in dopamine-mediated pathways, including mesocortical and mesolimbic pathways during initial recovery, as well as improved speech, behavior, and fatigue in the following months. The role of amantadine in the treatment of MBD warrants further study.

Disconnected Motor Intention and Spatial Attention in a Case of Probable Marchiafava-Bignami Disease

Marchiafava-Bignami disease (MBD) is a rare complication of chronic alcoholism that typically causes demyelination and necrosis of the corpus callosum. Here, we report a man with probable MBD with callosal and right medial paracentral lesions who presented with abnormal reaching behavior and ideomotor apraxia of the left hand. He exhibited difficulty in reaching with the left hand when a target object was placed on his right-hand side, and he exhibited rightward bias when using his right hand in a line bisection task. These disturbances in reaching suggest disruption of the top-down control of motor intention and spatial attention at the corpus callosum.

Splenial white matter integrity is associated with memory impairments in posterior cortical atrophy

Posterior cortical atrophy is an atypical form of Alzheimer’s disease characterized by visuospatial impairments and predominant tissue loss in the posterior parieto-occipital and temporo-occipital cortex. Whilst episodic memory is traditionally thought to be relatively preserved in posterior cortical atrophy, recent work indicates that memory impairments form a common clinical symptom in the early stages of the disease. Neuroimaging studies suggest that memory dysfunction in posterior cortical atrophy may originate from atrophy and functional hypoconnectivity of parietal cortex. The structural connectivity patterns underpinning these memory impairments, however, have not been investigated. This line of inquiry is of particular interest, as changes in white matter tracts of posterior cortical atrophy patients have been shown to be more extensive than expected based on posterior atrophy of grey matter. In this cross-sectional diffusion tensor imaging MRI study, we examine the relationship between white matter microstructure and verbal episodic memory in posterior cortical atrophy. We assessed episodic memory performance in a group of posterior cortical atrophy patients (n = 14) and a group of matched healthy control participants (n = 19) using the Free and Cued Selective Reminding Test with Immediate Recall. Diffusion tensor imaging measures were obtained for 13 of the posterior cortical atrophy patients and a second control group of 18 healthy adults. Patients and healthy controls demonstrated similar memory encoding performance, indicating that learning of verbal information was preserved in posterior cortical atrophy. However, retrieval of verbal items was significantly impaired in the patient group compared with control participants. As expected, tract-based spatial statistics analyses showed widespread reductions of white matter integrity in posterior cortical regions of patients compared with healthy adults. Correlation analyses indicated that poor verbal retrieval in the patient group was specifically associated with microstructural damage of the splenium of the corpus callosum. Post-hoc tractography analyses in healthy controls demonstrated that this splenial region was connected to thalamic radiations and the retrolenticular part of the internal capsule. These results provide insight into the brain circuits that underlie memory impairments in posterior cortical atrophy. From a cognitive perspective, we propose that the association between splenial integrity and memory dysfunction could arise indirectly via disruption of attentional processes. We discuss implications for the clinical phenotype and development of therapeutic aids for cognitive impairment in posterior cortical atrophy.