The relationship between handedness and risk of multiple sclerosis

Handedness in Alzheimer Disease: A Systematic Review

Handedness has been a topic of scientific interest for many years. However, false and misleading ideas have dominated this field with a still limited amount of research into the association with clinical disorders like Alzheimer disease (AD). In accordance with PRISMA guidelines, PubMed, Embase, and Cochrane Library were searched for studies regarding the association of handedness and AD. Twelve articles were included. Case-control studies show that left-handedness is not a risk factor for late-onset AD (LOAD). However, nonright handedness was found to be more prevalent in patients with early-onset AD (EOAD). Moreover, handedness does not seem to affect neuropsychological performance. We also show that collapsing versus separating mixed and left-handedness may yield different results. Future research on the relation between handedness and AD may provide new insight into disease pathogenesis, improve rehabilitation, and help identify patients who will progress, aiding the design of prevention trials.

The enigma and implications of brain hemispheric asymmetry in neurodegenerative diseases

The lateralization of the human brain may provide clues into the pathogenesis and progression of neurodegenerative diseases. Though differing in their presentation and underlying pathologies, neurodegenerative diseases are all devastating and share an intriguing theme of asymmetrical pathology and clinical symptoms. Parkinson’s disease, with its distinctive onset of motor symptoms on one side of the body, stands out in this regard, but a review of the literature reveals asymmetries in several other neurodegenerative diseases. Here, we review the lateralization of the structure and function of the healthy human brain and the common genetic and epigenetic patterns contributing to the development of asymmetry in health and disease. We specifically examine the role of asymmetry in Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, and multiple sclerosis, and interrogate whether these imbalances may reveal meaningful clues about the origins of these diseases. We also propose several hypotheses for how lateralization may contribute to the distinctive and enigmatic features of asymmetry in neurodegenerative diseases, suggesting a role for asymmetry in the choroid plexus, neurochemistry, protein distribution, brain connectivity and the vagus nerve. Finally, we suggest how future studies may reveal novel insights into these diseases through the lens of asymmetry.

Sensorimotor function does not predict quality of life in persons with multiple sclerosis

Quality of life (QOL) has been reported to be reduced in persons with multiple sclerosis. Further, associations between QOL and the clinical severity of the disease as well as sensorimotor function were shown. We reinvestigated impacting factors on QOL by the additional assessment of depression, fatigue, satisfaction with life, and a battery of end-effector based assessments of sensorimotor functioning. Models of multiple linear regression revealed everyday life activity limitations to be the driving factor within the used questionnaire and no association with sensorimotor tests, but depression, fatigue, and satisfaction with life. We conclude that either psycho-emotional coping and adaptability are the dominant determinant of QOL or that QOL is in need of a quantitative and objective reconceptualization.

Lateralization bias for autoimmune optic neuritis

The asymmetrical structure of the human brain is reflected not only by innate interhemispheric differences but also by lateralization in neurological disease. We tested if unilateral autoimmune optic neuritis (aON) manifests more frequently on the left than the right eye in clinical and neuroimaging terms and whether Google searches for aON symptoms reflect this bias, too. We employed a retrospective analysis of a patient cohort from 2009 to 2019 with 552 unilateral aONs and 374 corresponding MRI imaging data sets. Searchmetrics Suite keywords tool was applied for the analysis of Google searches on aON-symptoms in Germany, the US and the UK for the last 12 months. Left eye aON manifestations were more frequent than right aON manifestations (55.3% vs. 44.7%, p = 0.015) and 1.9 times more likely to be associated with a pathological MRI finding in the affected optic nerve (p = 0.013). Keywords describing aON-typical but not other ocular symptoms were more frequently associated with Google searches for the left in comparison to the right eye (p < 0.001). Autoimmune optic neuritis more frequently affects the left than the right eye and people search on the Internet more often for left-sided aON symptoms. Although a reporting bias due to an increased perception of left eye symptoms is one possible explanation, MRI evidence of more frequent optic nerve affection for the left in comparison to the right side suggests a leftward lateralization bias similar to the one previously shown for cerebral neuroinflammatory lesions.

Introduction of the Watzmann Severity Scale: A sensorimotor approach to estimate the course of inpatient rehabilitation in multiple sclerosis

Multiple sclerosis is an autoimmune disease with a plethora of potentially arising impairments and a coarse standard clinical estimation of severity, the expanded disability status scale (EDSS). In this study, we introduced the Watzmann Severity Scale (WSS), a sensorimotor function based statistical model of the EDSS of 113 patients. Using the WSS, we examined the rehabilitation course of 87 patients. The WSS revealed to be a reliable estimate of the EDSS with an R²_adjusted of 0.81, although lower EDSS grades were systematically overestimated. Further, patients slightly improved during their inpatient stay of in average 17d by 0.21 on the WSS, with changes in gait performance being the driving factor (|β|-weight of 0.84). We were not able to reliably predict changes in the WSS and found no association with the duration of hospitalization. We conclude and advise that rehabilitation should start earlier, if lower EDSS grades were not overestimated, to emphasize gait less in rehabilitation, and to change from a perspective of impairment and disability to performance in order to maximize patient rehabilitation.

The association between handedness and clinicodemographic characteristics in people with multiple sclerosis: a brief report

A relationship between handedness and clinicodemographic profiles of people with multiple sclerosis was sought using data from the Multiple Sclerosis Partners Advancing Technology Health Solutions network of 10 multiple sclerosis centers in the USA and Europe. Handedness data were available for 8888 multiple sclerosis patients, of which 917 (10.3%) were left-handed. Clinicodemographic profiles of right versus left-handed multiple sclerosis patients were similar except for a slightly increased proportion of men who were left-handed, and slightly reduced performance on the manual dexterity test using the non-dominant hand in left-handed patients. We found no evidence to suggest a prognostic implication of handedness in multiple sclerosis.

Ancestral Exposure to Stress Generates New Behavioral Traits and a Functional Hemispheric Dominance Shift

In a continuously stressful environment, the effects of recurrent prenatal stress (PS) accumulate across generations and generate new behavioral traits in the absence of genetic variation. Here, we investigated if PS or multigenerational PS across 4 generations differentially affect behavioral traits, laterality, and hemispheric dominance in male and female rats. Using skilled reaching and skilled walking tasks, 3 findings support the formation of new behavioral traits and shifted laterality by multigenerational stress. First, while PS in the F1 generation did not alter paw preference, multigenerational stress in the F4 generation shifted paw preference to favor left-handedness only in males. Second, multigenerational stress impaired skilled reaching and skilled walking movement abilities in males, while improving these abilities in females beyond the levels of controls. Third, the shift toward left-handedness in multigenerationally stressed males was accompanied by increased dendritic complexity and greater spine density in the right parietal cortex. Thus, cumulative multigenerational stress generates sexually dimorphic left-handedness and dominance shift toward the right hemisphere in males. These findings explain the origins of apparently heritable behavioral traits and handedness in the absence of DNA sequence variations while proposing epigenetic mechanisms.

Factors associated with onset, relapses or progression in multiple sclerosis: A systematic review

Multiple sclerosis (MS) is a chronic disease of the central nervous system with an unidentified etiology. We systematically reviewed the literature on the possible risk factors associated with MS disease onset, relapses and progression from 1960 to 2012 by accessing six databases and including relevant systematic reviews, meta-analyses, case-control or cohort studies. The focus was on identifying modifiable risk factors. Fifteen systematic reviews and 169 original articles were quality assessed and integrated into a descriptive review. Best evidence, which included one or more prospective studies, suggested that lower exposure to sunlight and/or lower serum vitamin D levels were associated with an increased risk of developing MS onset and subsequent relapses, but a similar quality of evidence was lacking for disease progression. Prospective studies indicated that cigarette smoking may increase the risk of MS as well as accelerate disease progression, but whether smoking altered the risk of a relapse was largely unknown. Infections were implicated in both risk of developing MS and relapses, but data for progression were lacking. Specifically, exposure to the Epstein-Barr virus, particularly if this manifested as infectious mononucleosis during adolescence, was associated with increased MS risk. Upper respiratory tract infections were most commonly associated with an increase in relapses. Relapse rates typically dropped during pregnancy, but there was no strong evidence to suggest that pregnancy itself altered the risk of MS or affected long-term progression. Emerging research with the greatest potential to impact public health was the suggestion that obesity during adolescence may increase the risk of MS; if confirmed, this would be of major significance.

Awake right hemisphere brain surgery

We report the indications and outcomes of awake right hemispheric brain surgery, as well as a rare patient with crossed aphasia. Awake craniotomies are often performed to protect eloquent cortex. We reviewed the medical records for 35 of 96 patients, in detail, who had awake right hemisphere brain operations. Intraoperative cortical mapping of motor and/or language function was performed in 29 of the 35 patients. A preoperative speech impairment and left hand dominance were the main indicators for awake right-sided craniotomies in patients with right hemisphere lesions. Four patients with lesion proximity to eloquent areas underwent awake craniotomies without cortical mapping. In addition, one patient had a broncho-pulmonary fistula, and another had a recent major cardiac procedure that precluded awake surgery. An eloquent cortex representation was identified in 14 patients (48.3%). Postoperatively, seven of 17 patients (41.1%) who presented with weakness, experienced improvements in their motor functions, 11 of 16 (68.7%) with seizures became seizure-free, and seven of nine (77.7%) with moderate to severe headaches and one of two with a visual field deficit improved significantly. There were also improvements in speech and language functions in all patients who presented with speech difficulties. A right sided awake craniotomy is an excellent option for left handed patients, or those with right sided cortical lesions that result in preoperative speech impairments. When combined with intraoperative cortical mapping, both speech and motor function can be well preserved.

Brain asymmetry, immunity, handedness

The principle of symmetry-asymmetry is widely presented in the structural and functional organization of the nonliving and living nature. One of the most complex manifestations of this principle is the left-right asymmetry of the human brain. The present review summarizes previous and contemporary literary data regarding the role of brain asymmetry in neuroimmunomodulation. Some handedness-related peculiarities are outlined additionally. Brain asymmetry is considered to be imprinted in the formation and regulation of the individual’s responses and relationships at an immunological level with the external and internal environment. The assumptions that the hemispheres modulate immune response in an asymmetric manner have been confirmed in experiments on animals. Some authors assume that the right hemisphere plays an indirect role in neuroimmunomodulation, controlling and suppressing the left hemispheric inductive signals.

Sensory handedness is not reflected in cortical responses after basic nerve stimulation: a MEG study

Motor dominance is well established, but sensory dominance is much less clear. We therefore studied the cortical evoked magnetic fields using magnetoencephalography (MEG) in a group of 20 healthy right handed subjects in order to examine whether standard electrical stimulation of the median and ulnar nerve demonstrated sensory lateralization. The global field power (GFP) curves, as an indication of cortical activation, did not depict sensory lateralization to the dominant left hemisphere. Comparison of the M20, M30, and M70 peak latencies and GFP values exhibited no statistical differences between the hemispheres, indicating no sensory hemispherical dominance at these latencies for each nerve. Field maps at these latencies presented a first and second polarity reversal for both median and ulnar stimulation. Spatial dipole position parameters did not reveal statistical left-right differences at the M20, M30 and M70 peaks for both nerves. Neither did the dipolar strengths at M20, M30 and M70 show a statistical left-right difference for both nerves. Finally, the Laterality Indices of the M20, M30 and M70 strengths did not indicate complete lateralization to one of the hemispheres. After electrical median and ulnar nerve stimulation no evidence was found for sensory hand dominance in brain responses of either hand, as measured by MEG. The results can provide a new assessment of patients with sensory dysfunctions or perceptual distortion when sensory dominance occurs way beyond the estimated norm.

Mixed handedness is associated with greater age-related decline in volumes of the hippocampus and amygdala: the PATH through life study

Handedness has been found to be associated with structural and functional cerebral differences. Left handedness and mixed handedness also appear to be associated with an elevated risk of some developmental and immunological disorders that may contribute to pathological processes developing in ageing. Inconsistent reports show that left handedness may be more prevalent in early-onset as well as late-onset Alzheimer's disease, but might also be associated with slower decline. Such inconsistencies may be due to handedness being usually modeled as a binary construct while substantial evidence suggests it to be a continuous trait. The aim of this study was to investigate the relationship between brain structures known to be implicated in pathological ageing and strength and direction of handedness. The association between handedness and hippocampal and amygdalar atrophy was investigated in 327 cognitively healthy older individuals. Handedness was measured with the Edinburgh Inventory. Two measures were computed from this index, one reflecting the direction (left = 0/right = 1) and the other the degree of handedness (ranging from 0 to 1). Hippocampal and amygdalar volumes were manually traced on scans acquired 4 years apart. Regression analyses were used to assess the relationship between strength and direction of handedness and incident hippocampal and amygdalar atrophy. Analyses showed that strength but not direction of handedness was a significant predictor of hippocampal (Left: beta = 0.118, P = 0.013; Right: beta = 0.116, P = 0.010) and amygdalar (Right: beta = 0.105, P = 0.040) atrophy. The present findings suggest that mixed but not left handedness is associated with greater hippocampal and amygdalar atrophy. This effect may be due to genetic, environmental, or behavioural differences that will need further investigation in future studies.

Increased risk of multiple sclerosis among women with migraine in the Nurses' Health Study II

BACKGROUND

The prospective Nurses' Health Study II (NHS-II), which enrolled over 116,000 female nurses, provides a unique opportunity to test the hypothesis of whether migraine is associated with multiple sclerosis (MS) and to explore the temporal aspects of the interrelationship.

OBJECTIVES

To calculate relative risk of MS among NHS-II participants with and without migraine and to estimate odds ratio (OR) of being diagnosed with migraine in women with and without pre-existing MS.

METHODS

Cox proportional hazards regression was used to estimate rate ratios and 95% confidence intervals (CIs) of being diagnosed with MS in women with and without pre-existing migraine adjusted for potential confounders. Multivariate adjusted ORs of being diagnosed with migraine in women with and without pre-existing MS were estimated using logistic regression.

RESULTS

The prevalence of migraine in women with MS at baseline (26%, p = 0.11) and those diagnosed with MS after enrolment (29%, p < 0.0001) was higher than in the non-MS cases (21%). The relative risk of developing MS in migraineurs was 1.39 times higher than in non-migraineurs (95% CI 1.10-1.77, p = 0.008). The absolute risk of developing MS in women migraineurs over a 15-year follow-up was 0.47% and among non-migraineurs 0.32%. The odds of being diagnosed with migraine was higher in women with pre-existing MS compared with those without MS, but did not reach statistical significance (OR = 1.57, 95% CI 0.97-2.52; p = 0.06).

CONCLUSIONS

Using a large, cohort of women-nurses, history of migraine was associated with an increased risk of MS. However, the difference in absolute risk of MS in migraineurs and non-migraineurs was small.