Cognitive impairment in multiple sclerosis

Attention Network Test reveals alerting network dysfunction in multiple sclerosis

Attention is one of the cognitive domains typically affected in multiple sclerosis. The Attention Network Test was developed to measure the function of the three distinct attentional networks, alerting, orienting, and executive control. The Attention Network Test has been performed in various neuropsychiatric conditions, but not in multiple sclerosis. Our objective was to investigate functions of attentional networks in multiple sclerosis by means of the Attention Network Test. Patients with relapsing—remitting multiple sclerosis (n = 57) and healthy controls (n = 57) matched for age, sex, and education performed the Attention Network Test. Significant differences between patients and controls were detected in the alerting network (p = 0.003), in contrast to the orienting (p = 0.696) and the conflict (p = 0.114) network of visual attention. Mean reaction time in the Attention Network Test was significantly longer in multiple sclerosis patients than in controls (p = 0.032), Multiple sclerosis patients benefited less from alerting cues for conflict resolution compared with healthy controls. The Attention Network Test revealed specific alterations of the attention network in multiple sclerosis patients which were not explained by an overall cognitive slowing.

The histopathology of grey matter demyelination in multiple sclerosis

Multiple sclerosis (MS) is characterized by focal demyelinating lesions in white matter (WM) and grey matter (GM) of the central nervous system. Results of studies using quantitative magnetic resonance imaging techniques indicate that GM MS pathology has a significant impact on clinical symptoms and disability in MS, and may occur partly independently of WM pathology. Subpial cerebral and cerebellar cortexes are predilection sites for demyelination in MS. Significant neuronal and axonal pathology has been detected in GM MS lesions. The pathology of MS lesions is location-dependent; there is less pronounced inflammation in GM lesion areas than in WM lesions. The presence and extent of GM lesions has recently been correlated to meningeal inflammation, and cells infected with the Epstein-Barr virus have been detected in meningeal infiltrates, suggesting a role of meningeal inflammation in cortical lesion pathogenesis.

Cognitive decline in multiple sclerosis: impact of topographic lesion distribution on differential cognitive deficit patterns

Background: Multiple sclerosis (MS) is often accompanied by cognitive dysfunction. A negative correlation between cerebral lesion load and atrophy and cognitive performance has been pointed out almost consistently. Further, the distribution of lesions might be critical for the emergence of specific patterns of cognitive deficits.

Objective: The current study evaluated the significance of total lesion area (TLA) and central atrophy for the prediction of general cognitive dysfunction and tested for a correspondence between lesion topography and specific cognitive deficit patterns.

Methods: Thirty-seven patients with MS underwent neuropsychological assessment and magnetic resonance imaging. Lesion burden and central atrophy were quantified. Patients were classified into three groups by means of individual lesion topography (punctiform lesions/periventricular lesions/confluencing lesions in both periventricular and extra-periventricular regions).

Results: TLA was significantly related to 7 cognitive variables, whereas third ventricle width was significantly associated with 20 cognitive parameters. The three groups differed significantly in their performances on tasks concerning alertness, mental speed, and memory function.

Conclusion: Third ventricle width as a straight-forward measure of central atrophy proved to be of substantial predictive value for cognitive dysfunction, whereas total lesion load played only a minor role. Periventricular located lesions were significantly related to decreased psychomotor speed, whereas equally distributed cerebral lesion load did not. These findings support the idea that periventricular lesions have a determinant impact on cognition in patients with MS.

Correlating human and animal studies of cocaine abuse and gene expression

Gene expression changes resulting from cocaine abuse in both humans and animal models have been studied for several decades. Although human studies have been very useful at illuminating cocaine-related expression changes, there are many factors complicating these studies, including the difficulty of obtaining high-quality postmortem brain tissue and patient comorbidities. Animal models of cocaine abuse have served as valuable additions to human data and allow examination of specific aspects of cocaine abuse, including immediate early gene expression and the molecular effects of abstinence and relapse. In total, human and animal studies of cocaine abuse have uncovered gene expression changes in the brain related to a number of molecular functions, including the extracellular matrix, synaptic communication and neuroplasticity, receptors, ion channels and transporters, oligodendrocytes and myelin, apoptosis and cell death, mitochondrial function, signal transduction, and transcription factors. In addition, the mitogen-activated protein kinase and synaptic long-term potentiation signal transduction pathways are highlighted as pathways in which multiple components are altered by cocaine. Pathways and processes affected by changes in gene expression that overlap among multiple species may be promising pharmacotherapeutic targets for reducing the behavioral effects of cocaine abuse and the relapse potential observed in humans.

Modern modularity and the road towards a modular psychiatry

We propose to use modules representing functional subunits of the brain as the substrates of pathogenetic factors in mental disorders. This approach is based on scientific evidence from neurophysiology and cognitive psychology regarding the organisation of the human brain in functionally discernible, not necessarily temporally or spatially stable subunits, which are interconnected in complex, often multilayered networks of neuronal circuits. Such a definition would reconcile modern network theories of brain function with localizationist models. Module-based diagnosis and therapy of mental disorders will be the goal of a modular psychiatry, which has the advantage that it is founded in neuroscientific evidence and does not rely on arbitrary definitions of mental disorders based mainly on clinical empiricism.

Should SDMT substitute for PASAT in MSFC? A 5-year longitudinal study

BACKGROUND

The multiple sclerosis functional composite (MSFC) includes the Paced Auditory Serial Addition test (PASAT) as a measure of cognition.

OBJECTIVES AND METHODS

We compared the MSFC incorporating the Symbol Digit Modalities test (SDMT) (MSFC [sdmt]) to the usually applied MSFC (MSFC [pasat]) in a sample of 46 ptients with relapsing-remitting MS who were followed over a five-year period. Magnetic resonance imaging was performed at baseline.

RESULTS

The Expanded Disability Status scale (EDSS) deteriorated significantly over 5 years (P < 0.01), but MSFC scores remained stable. MSFC [sdmt] correlated with EDSS at all time points of evaluation, but MSFC [pasat] correlated with EDSS only at baseline, 1, and 5 years. The 5-year EDSS correlated significantly with baseline MSFC [sdmt] and MSFC [pasat] but did not correlate after adjustment for baseline EDSS. No significant correlation was found at baseline between MSFC and imaging parameters (lesion load, brain parenchymal fraction [BPF], ventricular fraction, mean magnetization transfer ratio of lesions and normal-appearing brain tissue), but baseline BPF correlated significantly with changes of SDMT z score (P = 0.0003), MSFC [pasat] (P = 0.006), and MSFC [sdmt] (P = 0.0002) over 5 years.

CONCLUSION

We propose not to substitute PASAT by SDMT in the MSFC but to consider SDMT as a complementary useful approach to evaluate overall MS disease.

Neuroinflammation and synaptic plasticity: theoretical basis for a novel, immune-centred, therapeutic approach to neurological disorders

The fascinating capacity that the central nervous system (CNS) has for encoding and retaining memories is thought to be based on activity-dependent forms of synaptic plasticity. The CNS and the immune systems are known to be engaged in an intense bidirectional crosstalk, and glial cells are now viewed as a crucial third element of the synapse. In this opinion article, we review the principal mechanisms by which the immune system, and in particular immune diffusible mediators, influences synaptic transmission and the induction of brain plastic phenomena. Thereafter, we consider the potential implications of inflammation-related overexpression of diffusible mediators in the disruption of synaptic plastic processes and neuronal networks functioning during human neurological diseases. Finally, we propose that a more accurate characterization of the mechanisms underlying the immune-mediated control of synaptic plasticity could represent, in the future, the basis for the development of a novel immune-centred therapeutic approach to neurological disorders.

Cognitive dysfunction 24–31 years after isolated optic neuritis

Objective

Cognitive dysfunction is common in multiple sclerosis (MS), but long-term data on cognition in patients with clinically isolated syndromes are sparse.

Methods

We determined cognitive functions in 22 patients 44–75 years old diagnosed with optic neuritis 24–31 years earlier but had no further clinical bouts and had not progressed clinically to MS. We used a neuropsychological test battery covering nine cognitive domains. Magnetic resonance imaging (MRI) of the brain had been performed earlier and was normal in six patients and showed two or more white matter abnormalities compatible with demyelinating lesions in 16 patients.

Results

On neuropsychological testing, one patient was within normal range on all tests, six subjects showed borderline results, and 15 patients (68%) showed significantly impaired performance in at least one cognitive domain. Seven patients showed significant impairment in two or more domains. Executive function, visuo-spatial ability, and information processing speed were the most frequently affected domains. There was no apparent correlation between MRI findings and cognitive function.

Conclusions

We conclude that cognitive dysfunction is common in patients many years after clinically isolated optic neuritis. Cognitive dysfunction was found even in patients who had no apparent demyelinating lesions on follow-up MRI.