In vivo assessment of peripheral nerve regeneration by diffusion tensor imaging

Peripheral neuropathy: assessment of proximal nerve integrity by diffusion tensor imaging

INTRODUCTION

We investigated the utility of diffusion tensor imaging (DTI) for detecting neuropathic changes in proximal nerve segments in patients with peripheral neuropathy.

METHODS

Twenty-one individuals with (n = 11) and without (n = 10) peripheral neuropathy underwent DTI of a defined sciatic nerve segment. Patients and controls were evaluated by clinical examination and nerve conduction studies at baseline and 6 months after the initial DTI scan.

RESULTS

The mean fractional anisotropy (FA) value was significantly lower in sciatic nerves from patients with peripheral neuropathy as compared with controls. Sciatic nerve FA values correlated with clinical disability scores and electrophysiological parameters of axonal damage at baseline and 6 months after MRI scan.

CONCLUSIONS

DTI-derived FA values are a sensitive measure to discriminate healthy from functionally impaired human sciatic nerve segments. DTI of proximal nerve segments may be useful for estimating the proximal axonal degeneration burden in patients with peripheral neuropathies.

Experimental video analysis of eye blink reflex in a primate model

BACKGROUND

The establishment of reliable methods for functional assessment in experimental models of peripheral nerve regeneration is crucial.

METHODS

We present a straightforward method for video analysis of the eye blink reflex in a model of facial nerve damage in a nonhuman primate (Callithrix sp.).

RESULTS

Our 6-level dynamic analysis demonstrated good reproducibility between independent observers, as measured by Cohen's kappa index. Our static analysis, which was based on 4 semiautomated metric parameters, showed low correlation during the early stage of facial movement recovery (the first and second weeks), but the correlation was excellent during the later stage of recovery (the third and fourth weeks).

CONCLUSION

Altogether, our results establish a viable and readily accessible method with good reproducibility and correlation for the analysis of functional facial nerve recovery in an experimental model and based on video images of the eye blink reflex.

Anatomic MR imaging and functional diffusion tensor imaging of peripheral nerve tumors and tumorlike conditions

BACKGROUND AND PURPOSE

A number of benign and malignant peripheral nerve tumor and tumorlike conditions produce similar imaging features on conventional anatomic MR imaging. Functional MR imaging using DTI can increment the diagnostic performance in differentiation of these lesions. Our aim was to evaluate the role of 3T anatomic MR imaging and DTI in the characterization of peripheral nerve tumor and tumorlike conditions.

MATERIALS AND METHODS

Twenty-nine patients (13 men, 16 women; mean age, 41±18 years; range, 11-83 years) with a nerve tumor or tumorlike condition (25 benign, 5 malignant) underwent 3T MR imaging by using anatomic (n=29), functional diffusion, DWI (n=21), and DTI (n=24) techniques. Images were evaluated for image quality (3-point scale), ADC of the lesion, tractography, and fractional anisotropy of nerves with interobserver reliability in ADC and FA measurements.

RESULTS

No significant differences were observed in age (benign, 40±18 versus malignant, 45±19 years) and sex (benign, male/female=12:12 versus malignant, male/female=3:2) (P>.05). All anatomic (29/29, 100%) MR imaging studies received "good" quality; 20/21 (95%) DWI and 21/24 (79%) DTI studies received "good" quality. ADC of benign lesions (1.848±0.40×10(-3) mm2/s) differed from that of malignant lesions (0.900±0.25×10(-3) mm2/s, P<.001) with excellent interobserver reliability (ICC=0.988 [95% CI, 0.976-0.994]). There were no FA or ADC differences between men and women (P>.05). FA of involved nerves was lower than that in contralateral healthy nerves (P<.001) with excellent interobserver reliability (ICC=0.970 [95% CI, 0.946-0.991]). ADC on DTI and DWI was not statistically different (P>.05), with excellent intermethod reliability (ICC=0.943 [95% CI, 0.836-0.980]). Tractography differences were observed in benign and malignant lesions.

CONCLUSIONS

3T MR imaging and DTI are valuable methods for anatomic and functional evaluation of peripheral nerve lesions with excellent interobserver reliability. While tractography and low FA provide insight into neural integrity, low diffusivity values indicate malignancy in neural masses.

Anti-obesity sodium tungstate treatment triggers axonal and glial plasticity in hypothalamic feeding centers

Objective

This study aims at exploring the effects of sodium tungstate treatment on hypothalamic plasticity, which is known to have an important role in the control of energy metabolism.

Methods

Adult lean and high-fat diet-induced obese mice were orally treated with sodium tungstate. Arcuate and paraventricular nuclei and lateral hypothalamus were separated and subjected to proteomic analysis by DIGE and mass spectrometry. Immunohistochemistry and in vivo magnetic resonance imaging were also performed.

Results

Sodium tungstate treatment reduced body weight gain, food intake, and blood glucose and triglyceride levels. These effects were associated with transcriptional and functional changes in the hypothalamus. Proteomic analysis revealed that sodium tungstate modified the expression levels of proteins involved in cell morphology, axonal growth, and tissue remodeling, such as actin, CRMP2 and neurofilaments, and of proteins related to energy metabolism. Moreover, immunohistochemistry studies confirmed results for some targets and further revealed tungstate-dependent regulation of SNAP25 and HPC-1 proteins, suggesting an effect on synaptogenesis as well. Functional test for cell activity based on c-fos-positive cell counting also suggested that sodium tungstate modified hypothalamic basal activity. Finally, in vivo magnetic resonance imaging showed that tungstate treatment can affect neuronal organization in the hypothalamus.

Conclusions

Altogether, these results suggest that sodium tungstate regulates proteins involved in axonal and glial plasticity. The fact that sodium tungstate could modulate hypothalamic plasticity and networks in adulthood makes it a possible and interesting therapeutic strategy not only for obesity management, but also for other neurodegenerative illnesses like Alzheimer’s disease.

3T MR tomography of the brachial plexus: structural and microstructural evaluation

Magnetic resonance (MR) neurography comprises an evolving group of techniques with the potential to allow optimal noninvasive evaluation of many abnormalities of the brachial plexus. MR neurography is clinically useful in the evaluation of suspected brachial plexus traumatic injuries, intrinsic and extrinsic tumors, and post-radiogenic inflammation, and can be particularly beneficial in pediatric patients with obstetric trauma to the brachial plexus. The most common MR neurographic techniques for displaying the brachial plexus can be divided into two categories: structural MR neurography; and microstructural MR neurography. Structural MR neurography uses mainly the STIR sequence to image the nerves of the brachial plexus, can be performed in 2D or 3D mode, and the 2D sequence can be repeated in different planes. Microstructural MR neurography depends on the diffusion tensor imaging that provides quantitative information about the degree and direction of water diffusion within the nerves of the brachial plexus, as well as on tractography to visualize the white matter tracts and to characterize their integrity. The successful evaluation of the brachial plexus requires the implementation of appropriate techniques and familiarity with the pathologies that might involve the brachial plexus.