Magnetic Resonance Spectroscopy and Environmental Toxicant Exposure

VALUES†: a national multicenter study of regional and gender differences in frontotemporal disease in amyotrophic lateral sclerosis

SUMMARY Aims: To investigate regional and gender differences in prevalence rates and the pattern of cognitive and behavioral impairment in amyotrophic lateral sclerosis. Materials & methods: One hundred and ten subjects (55 male) from 14 amyotrophic lateral sclerosis clinics were cross-sectionally evaluated with the Penn State Brief Exam of frontal and temporal dysfunction syndromes. Results: Prevalence rates of cognitive impairment and behavioral impairment were statistically equivalent among rural, suburban and urban subgroups. Females evidenced significant strengths in fluency and limitations in configurational processing. Patterns of regional findings suggested greater frontal cortical involvement in the rural sample. Females demonstrated more bihemispheric involvement in comparison to more left hemispheric involvement for males. Conclusions: Regional prevalence differences in frontotemporal disease prodrome appear insignificant and multifactorial, while being consistent with the toxicity model implicating pesticides in frontal lobe change. Female gender potentially masks the frontotemporal disease prodrome due to a bilateral distribution of language processing, which requires an assessment of right hemisphere-mediated capacities to detect.

Neurochemical changes in welders revealed by proton magnetic resonance spectroscopy

BACKGROUND

Occupational and environmental exposure to manganese (Mn) is associated with various neurobehavioral and movement dysfunctions. However, few studies have systemically examined the neurochemical effects of Mn exposure.

OBJECTIVES

We examined typical changes in cerebral metabolite ratios in welders chronically exposed to Mn, compared with control individuals, using proton magnetic resonance spectroscopy (MRS), investigated whether an abnormality in brain metabolism is associated with neurobehavioral changes, and assessed possible implications of chronic Mn exposure.

METHODS

Thirty-five welders chronically exposed to Mn and 20 age-matched healthy subjects underwent single-voxel MRS at short echo time to assess the N-acetylaspartate (NAA), myoinositol (mI), total choline (tCho), and glutamine plus glutamate (Glx) levels, each of which was expressed as a ratio to total creatine (tCr). Neurobehavioral tests were also performed to define cognitive status.

RESULTS

NAA/tCr, Glx/tCr, and tCho/tCr ratios in the frontal gray matter (anterior cingulate cortex; ACC) and parietal white matter did not differ significantly between welders and control subjects. These metabolite ratios did not correlate significantly with blood Mn concentration or neurobehavioral parameters. However, mI levels in the ACC, but not in the parietal white matter, were significantly reduced in welders compared with control individuals (P<0.01). Furthermore, in the frontal lobe of the brain, the mI/tCr ratio was significantly correlated with verbal memory scores as well as blood Mn concentration (P<0.05).

CONCLUSIONS

The cognitive decline observed in welders exposed to Mn was associated with a decreased mI/tCr ratio in the ACC. The depletion of mI in welders may reflect possible glial cell swelling and/or detoxification processes associated with long-term exposure to Mn.