Selective decrease of small sensory neurons in lumbar dorsal root ganglia labeled with horseradish peroxidase after ND:YAG laser irradiation of the tibial nerve in the rat

Temporal disconnection between pain relief and trigeminal nerve microstructural changes after Gamma Knife radiosurgery for trigeminal neuralgia

OBJECTIVE

Gamma Knife radiosurgery (GKRS) is a noninvasive surgical treatment option for patients with medically refractive classic trigeminal neuralgia (TN). The long-term microstructural consequences of radiosurgery and their association with pain relief remain unclear. To better understand this topic, the authors used diffusion tensor imaging (DTI) to characterize the effects of GKRS on trigeminal nerve microstructure over multiple posttreatment time points.

METHODS

Ninety-two sets of 3-T anatomical and diffusion-weighted MR images from 55 patients with TN treated by GKRS were divided within 6-, 12-, and 24-month posttreatment time points into responder and nonresponder subgroups (≥ 75% and < 75% reduction in posttreatment pain intensity, respectively). Within each subgroup, posttreatment pain intensity was then assessed against pretreatment levels and followed by DTI metric analyses, contrasting treated and contralateral control nerves to identify specific biomarkers of successful pain relief.

RESULTS

GKRS resulted in successful pain relief that was accompanied by asynchronous reductions in fractional anisotropy (FA), which maximized 24 months after treatment. While GKRS responders demonstrated significantly reduced FA within the radiosurgery target 12 and 24 months posttreatment (p < 0.05 and p < 0.01, respectively), nonresponders had statistically indistinguishable DTI metrics between nerve types at each time point.

CONCLUSIONS

Ultimately, this study serves as the first step toward an improved understanding of the long-term microstructural effect of radiosurgery on TN. Given that FA reductions remained specific to responders and were absent in nonresponders up to 24 months posttreatment, FA changes have the potential of serving as temporally consistent biomarkers of optimal pain relief following radiosurgical treatment for classic TN.

Is low-level laser therapy in relieving neck pain effective? Systematic review and meta-analysis

The aim of this study is to determine the efficacy of low-level laser therapy (LLLT) in reducing acute and chronic neck pain as measured by the visual analog scale (VAS). A systematic search of nine electronic databases was conducted to identify original articles. For study selection, two reviewers independently assessed titles, abstracts, and full text for eligibility. Methodological quality was assessed using the Detsky scale. Data were analyzed using random-effects model in the presence of heterogeneity and fixed-effect model in its absence. Heterogeneity was assessed using Cochran's Q statistic and quantifying I (2). Risk ratios (RR) with 95 % confidence intervals (CI) were reported. Eight randomized controlled trials involving 443 patients met the strict inclusion criteria. Inter-rater reliability for study selection was 92.8 % (95 % CIs 80.9-100 %) and for methodological quality assessment was 83.9 % (95 % CIs 19.4-96.8 %). Five trials included patients with cervical myofascial pain syndrome (CMPS), and three trials included different patient populations. A meta-analysis of five CMPS trials revealed a mean improvement of VAS score of 10.54 with LLLT (95 % CI 0.37-20.71; Heterogeneity I (2 )= 65 %, P = 0.02). This systematic review provides inconclusive evidence because of significant between-study heterogeneity and potential risk of bias. The benefit seen in the use of LLLT, although statistically significant, does not constitute the threshold of minimally important clinical difference.

Effects of 904-nm low-level laser therapy in the management of lateral epicondylitis: a randomized controlled trial

OBJECTIVE

The aim of this study was to evaluate the effectiveness of 904-nm low-level laser therapy (LLLT) in the management of lateral epicondylitis.

BACKGROUND DATA

Lateral epicondylitis is characterized by pain and tenderness over the lateral elbow, which may also result in reduction in grip strength and impairment in physical function. LLLT has been shown effective in its therapeutic effects in tissue healing and pain control.

METHODS

Thirty-nine patients with lateral epicondylitis were randomly assigned to receive either active laser with an energy dose of 0.275 J per tender point (laser group) or sham irradiation (placebo group) for a total of nine sessions. The outcome measures were mechanical pain threshold, maximum grip strength, level of pain at maximum grip strength as measured by the Visual Analogue Scale (VAS) and the subjective rating of physical function with Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire.

RESULTS

Significantly greater improvements were shown in all outcome measures with the laser group than with the placebo group (p < 0.0125), except in the two subsections of DASH.

CONCLUSION

This study revealed that LLLT in addition to exercise is effective in relieving pain, and in improving the grip strength and subjective rating of physical function of patients with lateral epicondylitis.

Efficacy of 904 nm gallium arsenide low level laser therapy in the management of chronic myofascial pain in the neck: A double-blind and randomize-controlled trial

BACKGROUND AND OBJECTIVES

A prospective, double-blind, randomized, and controlled trial was conducted in patients with chronic myofascial pain syndrome (MPS) in the neck to evaluate the effects of infrared low level 904 nm Gallium-Arsenide (Ga-As) laser therapy (LLLT) on clinical and quality of life (QoL).

STUDY DESIGN/PATIENTS AND METHODS

The study group consisted of 60 MPS patients. Patients were randomly assigned to two treatment groups: Group I (actual laser; 30 patients) and Group II (placebo laser; 30 patients). LLLT continued daily for 2 weeks except weekends. Follow-up measures were evaluated at baseline, 2, 3, and 12 weeks. All patients were evaluated with respect to pain at rest, pain at movement, number of trigger points (TP), the Neck Pain and Disability Visual Analog Scale (NPAD), Beck depression Inventory (BDI), and the Nottingham Health Profile (NHP).

RESULTS

In active laser group, statistically significant improvements were detected in all outcome measures compared with baseline (P < 0.01) while in the placebo laser group, significant improvements were detected in only pain score at rest at the 1 week later of the end of treatment. The score for self-assessed improvement of pain was significantly different between the active and placebo laser groups (63 vs. 19%) (P < 0.01).

CONCLUSION

This study revealed that short-period application of LLLT is effective in pain relief and in the improvement of functional ability and QoL in patients with MPS.

Delayed loss of small dorsal root ganglion cells after transection of the rat sciatic nerve

The present study deals with changes in numbers and sizes of primary afferent neurons (dorsal root ganglion [DRG] cells) after sciatic nerve transection. We find that this lesion in adult rats leads to death of some DRG cells by 8 weeks and 37% by 32 weeks after the lesion. The loss of cells appears earlier in and is more severe in B-cells (small, dark cells with unmyelinated axons) than A-cells (large, light cells with myelinated axons). With regard to mean cell volumes, there is a tendency for both categories of DRG cells to be smaller, but except for isolated time points, these differences are not statistically significant. These findings differ from most earlier reports in that the cell loss takes place later than usually reported, that the loss is more severe for B-cells, and that neither A- or B-cells change size significantly. Accordingly, we conclude that sciatic nerve transection in adult rats leads to a slowly developing but relatively profound loss of primary afferent neurons that is more severe for B-cells. These results can serve as a basis for studies to determine the effectiveness of trophic or survival factors in avoiding axotomy induced cell death.

Effect of pulsed Nd:YAG laser radiation on action potential conduction in isolated mammalian spinal nerves

BACKGROUND AND OBJECTIVE

Dental lasers are claimed to produce analgesia, but the mechanisms and extent of any effects are uncertain. This study investigated the effects of lasing on nerve conduction in isolated nerves.

STUDY DESIGN/MATERIALS AND METHODS

Pulsed Nd:YAG laser energy was applied to spinal nerves in vitro and effects were measured as attenuation of the compound action potential (CAP) evoked by electrical stimulation.

RESULTS

Lasing for 1 minute at 0.3-3.0 W caused a dose-dependent attenuation of all components of the CAP (P < 0.03). With 0.3-1.0 W power, the CAP recovered to > 95% of the control levels 7 minutes after lasing; recovery was incomplete after lasing at > 2.0 W.

CONCLUSION

Isolated nerves were remarkably tolerant of lasing. The degree of nerve conduction block increased with laser power. The data indicate that lasing could diminish sensations, including pain, mediated by peripheral nerves in soft tissues.

Loss of dorsal root ganglion cells concomitant with dorsal root axon sprouting following segmental nerve lesions

Tight ligation of the fifth and sixth lumbar segmental nerves in the rat provides a model of neuropathic pain. We used this model to assess the changes in primary afferent input to the dorsal horn in neuropathic pain syndromes. Dorsal roots and ganglia were examined for up to 32 weeks following segmental nerve ligation. Stereologic and morphometric techniques revealed a notable decrease in the numbers of dorsal root ganglion cells and unmyelinated dorsal root axons by six weeks post-injury. By 32 weeks following segmental nerve ligations, the numbers of dorsal root ganglion cells have dropped to 50% of pre-ligation levels while the numbers of dorsal root axons have increased to normal levels predominantly due to sprouting of myelinated fibres. These findings indicate that although there is a great loss of dorsal root ganglion cells, there is dramatic sprouting of myelinated fibres and possibly some sprouting of unmyelinated fibres in the dorsal roots. Additionally, a difference in the responses of unmyelinated and myelinated fibres to this peripheral nerve injury is revealed. These changes in dorsal root ganglion cells and their central axons may underlie certain aspects of abnormal pain syndromes because of changes in the types and quantity of input the dorsal horn receives.

Long-term local corticosteroid application does not influence nerve transmission or structure

The long-term effects of a locally applied depot form of a corticosteroid on the electrical properties and structure of nerves were investigated in an animal experimental model. The conduction in electrically stimulated A-fibres of the plantar nerve was monitored by a bipolar volley recording of the sciatic nerve whereas the conduction in C-fibres of the plantar nerve was measured through a C-fibre evoked segmental flexion reflex in the anaesthetized rat. Droplets of either methylprednisolone acetate or vehicle were placed under direct observation on the plantar nerve. Saline was used as a control on the contralateral side. One to two weeks after the application both the A-fibre volley of the sciatic nerve and the C-fibre evoked reflex discharge of flexor motoneurons were recorded. No difference was found between the nerves treated with corticosteroid, constituent vehicle or saline. Light and electron microscopic analysis of the nerves showed no changes in the nerve fibres or in the intraneural connective tissue in either the corticosteroid treated or the control nerves. It is concluded that locally applied corticosteroids in limited amounts have no long-term effects on the electrical and structural properties of peripheral nerves.

Changes in sensory neuropeptides in dorsal root ganglion and spinal cord of spontaneously diabetic BB rats. A quantitative immunohistochemical study

This study examined the expression of the sensory neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), in the lumbar 4 and 5 dorsal root ganglion (DRG) and spinal cord of spontaneously diabetic BB rats and non-diabetic controls using quantitative immunohistochemical analysis. In both animal groups immunoreactivities for CGRP and SP were widely distributed within the neurons of DRG and in nerve fibres of the dorsal spinal cord. Image analysis of each neuropeptide subpopulation in the DRG showed that in diabetic rats the cell diameter of immunostained CGRP neurons was significantly decreased compared with controls, while no difference could be found for SP-immunoreactive (IR) neurons. The decrease in the CGRP-IR cell diameter appeared to occur mainly in medium to large neurons (30-50 microns diameter; 2.2% controls, < 1% diabetes), this change being parallel to an increased frequency of small-size neurons (< 20 microns diameter) in diabetic rats (62% controls, 69% diabetes; P < 0.05). However, there was no statistical difference in the total number of cells immunostained for either CGRP or SP between control and diabetic rats. The ratio of CGRP or SP neurons compared to total cells in the ganglion was similar in control and diabetic groups. No difference could be observed for peptide immunoreactivity in the dorsal and ventral horns of either control or diabetic animals. The observed changes of perikaryal size in diabetic rats might relate to the reduced axonal calibre and conduction velocity observed in these animals, and indicate that subpopulations of sensory neurons are affected differently by diabetes.

Increased number of sciatic sensory neurons in vitamin-E-deficient rats

The number and morphometric characteristics of sciatic sensory neurons were studied in Vitamin-E-deficient rats. Horseradish peroxidase (HRP) was injected into the sciatic nerves of normal and vitamin-E-deficient rats of the same age, and retrogradely labeled sensory neurons were counted and measured. The study was also carried out in rats that had previously undergone sciatic nerve crush, in order to observe the effects of axotomy on primary sensory neurons. In vitamin-E-deficient rats the number of sciatic sensory neurons was significantly higher than normal, with an increase of about 30%, in agreement with a previous finding concerning total population of primary sensory neurons in lumbar dorsal root ganglia (DRGs) of vitamin-E-deficient rats. The increase involved the small cell classes in particular. Axotomy induced similar percentages of neuron loss in normal and in vitamin-E-deficient rats (about 40%). In the latter, death affected small cell classes in particular--that is, the same classes that had increased in number in vitamin-E-deficient rats by comparison with controls. These results, together with previous findings, suggest that neurogenesis may occur in DRGs of vitamin-E-deficient rats.