Resistance to axonal degeneration after nerve compression in experimental diabetes

A Minimally Invasive Full Endoscopic Approach to Tibial Nerve Neurolysis in Diabetic Foot Neuropathy: An Alternative to Open Procedures

BACKGROUND

Dellon et al. have reported that chronic nerve compression of the tibial nerve inside the tarsal tunnel, caused by diabetes mellitus, can be relieved following open decompression surgery. However, the large skin incision resulting from Dellon's procedure may cause wound healing problems. The authors report the possibility of a minimally invasive full endoscopic procedure.

METHODS

Operations were performed under local anesthesia without a pneumatic tourniquet. An anesthetic agent was applied at the proximal part of the flexor retinaculum of the foot, and a hypodermic needle was advanced into the tarsal tunnel. Tarsal tunnel pressure and blood circulation of the tibial nerve using indocyanine green assessment were measured preoperatively. One 1-cm portal skin incision was made at the anesthetized area and the Universal Subcutaneous Endoscope system was inserted into the tarsal tunnel. The flexor retinaculum, tibial nerve, blood vessels, and abductor hallucis muscle fascia were identified under endoscopic observation. After decompression of the tarsal tunnel, the authors measured tarsal tunnel pressure and blood circulation of the tibial nerve for analysis of the effectiveness of the endoscopic decompression during the procedure.

RESULTS

Fourteen operations were compiled and analyzed. Postoperative clinical status was improved based on the preoperative modified Toronto Clinical Neuropathy Score. The mean tarsal tunnel pressure dropped to 4.5 mmHg during surgery from the initial preoperative 49.4 mmHg in resting position. Endoscopic indocyanine green assessment showed more than 30 percent improvement of the vascularity surrounding the tibial nerve.

CONCLUSION

The authors' minimally invasive full endoscopic procedure is a viable alternative approach for tarsal tunnel syndrome patients with diabetic foot neuropathy.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Morphological and hemodynamic changes of sciatic nerves and their vasa nervorum during circular compression and relaxation

The main aim of this study was to evaluate the biomechanical and hemodynamic responses of vasa nervorum under transverse circular compression. In situ compress-and-hold experiments were performed on the sciatic nerves of healthy and diabetic rats, and the blood flow within the vasa nervorum was observed using Doppler-optical coherence tomography. A new technique was developed to obtain the time-course of the cross sectional area and the morphology of the vasa nervorum from the tomographic images. A quasi-linear viscoelastic model was used to investigate the overall biomechanical properties of the nerves, and a two-dimensional three-layered finite element model was constructed to analyze the distribution of stress and the morphological changes during the compression-relaxation process. The results showed that the lumenal area of vasa nervorum was reduced in the compression stage, especially for the diabetic nerves. The reduction was greater than 70% when the reduction of the nerve diameter was only 10%. The quasi-linear viscoelastic model showed that normal nerves were more elastic but less viscous than the diabetic nerves. The finite element analyses demonstrated that perineurium could sustain more stress than other layers, while epineurium served as a cushion to protect vasa nervora. In addition, there were regions within epineurium with less stress, so that vasa nervora in these saddle regions were less deformed. The vasa nervorum in diabetic rats was more prone to compression and reduction of blood flow than that of the normal rats. The histological studies supported the simulation results.

Nerve decompression and neuropathy complications in diabetes: Are attitudes discordant with evidence?

External neurolysis of the nerve at fibro-osseous tunnels has been proprosed to treat or prevent signs, symptoms, and complications in the lower extremity of diabetes patients with sensorimotor polyneuropathy. Nerve decompression is justified in the presence of symptomatic compressed nerves in the several fibro-osseous tunnels of the extremities, which are known to be frequent in diabetes. Quite a body of literature has accumulated reporting results after such nerve decompression in the leg, describing pain relief and sensibility improvement, as well as balance recovery, diabetic foot ulcer prevention, curtailed ulcer recurrence risk, and amputation avoidance. Historical academic hesitance to endorse surgical treatments for pain and numbness in diabetes was based primarily on the early retrospective reports' potential for bias and placebo effects, and that the hypothetical basis for surgery lies outside the traditional etiology paradigm of length-dependent axonopathy. This reticence is here critiqued in view of recent studies using objective, measured outcome protocols which nullify such potential confounders. Pain relief is now confirmed with Level 1 studies, and Level 2 prospective information suggests protection from initial diabetic foot ulceration and most neuropathic ulcer recurrences. In view of the potential for nerve decompression to be useful in addressing some of the more difficult, expensive, and life altering complications of diabetic neuropathy, this secondary compression thesis and operative treatment methodology may deserve reassessment.

Decompressive Surgery for Diabetic Neuropathy: Waiting for Incontrovertible Proof

: Triple decompression surgery has been advocated as a treatment for diabetic peripheral neuropathy (DPN). A practice advisory published in 2006 by the American Academy of Neurology concluded that "this treatment alternative should be considered unproven." Since then, multiple cohort studies involving several thousands of patients and 1 nonblind, randomized, controlled trial have been published, suggesting that surgical treatment of DPN has become commonplace in many centers globally. The results of these observational studies suggest that decompressive surgery could result in a substantial reduction of pain and the restoration of sensation in patients with DPN. However, as these studies are all observational in design, the utility of surgery remains unproven. Furthermore, the selection of patients for surgery is based on the incorrect assumption that the presence of a Tinel sign at sites of potential entrapment indicates nerve compression. The utility of surgery could be determined through a randomized, double-blind, sham-controlled trial in which 1 leg is treated with surgical decompression and the other with sham surgery. This design would eliminate a large number of possible confounders and would therefore require only a small number of patients. Such a trial is currently being performed at the University of Texas. The true beneficiaries will be patients with DPN: either decompressive surgery will be established as an evidence-based treatment for millions of patients or they will be spared from potentially harmful surgery with no significant benefit.

ABBREVIATION

DPN, diabetic peripheral neuropathy.

Rationale, Science, and Economics of Surgical Nerve Decompression for Diabetic Neuropathy Foot Complications

Nerve decompression is effective and safe for dealing with the pain and numbness symptoms of the frequent nerve compression entrapments in diabetic symmetric peripheral neuropathy (DSPN). Evidence has accumulated of balance and stability improvements and protection against diabetic foot ulceration, recurrence and its complication cascade. Nerve decompression proffers significant benefit versus the large socioeconomic costs of DSPN complications. Advancing understanding of the mechanism of nerve compression and altered axonal activity in diabetes clarifies the basis of clinical benefit. Clinicians should seek out and recognize nerve entrapments and consider advising nerve decompression for relief of DSPN symptoms and prevention of complications.

The Positive Effect of Neurolysis on Diabetic Patients with Compressed Nerves of the Lower Extremities: A Systematic Review and Meta-analysis

Background:

Despite proven benefits of upper extremity nerve decompression in diabetics, neurolysis for diabetic patients with lower extremity (LE) nerve compression remains controversial.

Methods:

A search of ClinicalTrials.gov and Cochrane clinical trials registries, CENTRAL (The Cochrane Library), MEDLINE, EMBASE, LILACS, CINAHL, SCOPUS, and Google Scholar from 1962 to 2012, yielded 1956 citations. Any potential randomized or quasi-randomized controlled trials and observational cohort studies of diabetics with neurolysis of the common peroneal nerve, deep peroneal nerve, or tibial nerve were assessed. We included articles in any language that 1) provided information about diabetic patients who had neurolysis for symptomatic nerve compression diagnosed by (+) Tinel sign or electrodiagnostic study, and 2) quantified outcomes for pain, sensibility, or ulcerations/amputations. Case reports, review articles, animal or cadaver studies, and studies with <10 patients were excluded. We assessed pain relief, recovery of sensibility, and postoperative incidence of ulcerations/amputations at follow-up >3 months. A meta-analysis of descriptive statistics was performed.

Results:

Ten clinical series with a mean clinical relevance score of 70% and a mean methodologic quality score of 50% met inclusion criteria. We included 875 diabetic patients and 1053 LEs. Pain relief >3 points on visual analog scale occurred in 91% of patients; sensibility improved in 69%. Postoperative ulceration/amputation incidence was significantly reduced compared to preoperative incidence (odds ratio = 0.066, 95% confidence interval = 0.026–0.164, P < 0.0001).

Conclusions:

Observational data suggest that neurolysis significantly improves outcomes for diabetic patients with compressed nerves of the LE. No randomized controlled trials have been published.

In situ transverse elasticity and blood perfusion change of sciatic nerves in normal and diabetic rats

BACKGROUND

Diabetic neuropathy is the most pervasive complication of diabetes mellitus and its etiopathology is not completely elucidated. The existing literature focuses on the histological and structural changes as well as the longitudinal mechanical properties of nerves. The main objective of this study is to investigate the in situ transverse biomechanical properties and changes of microcirculation of sciatic nerves in diabetic and normal control rats.

METHODS

Quasi-static circular compression experiments were conducted on sciatic nerves of six normal and six diabetic Wistar rats. Local blood perfusion during the compression was also measured by laser Doppler flowmetry. The compressive stress and strain were estimated, in order to calculate the apparent Young's modulus. The impact of diabetes on peripheral nerves was examined by analyzing the transverse elasticity and microcirculation changes.

FINDINGS

The mean transverse apparent Young's modulus of the sciatic nerves in diabetic rats was 210.7 kPa, which was nearly two times greater than that of normal controls (116.3 kPa). The pressure threshold that blood perfusion started to decrease in diabetic rats (24.1 mm Hg) was smaller than in the normal controls (47.1 mm Hg).

INTERPRETATION

These results suggest that the sciatic nerve was stiffer in the diabetic rats. The structural changes in microvessels might lead to earlier decrease of blood perfusion in diabetic nerves under radial compression. These results provide information about the biomechanical and microcirculation changes of peripheral nerves inflicted by diabetes and may also serve as a reference for clinical nerve repair and regeneration for patients with diabetic neuropathy.

Decompressive surgery of lower limbs for symmetrical diabetic peripheral neuropathy

BACKGROUND

Symmetrical peripheral neuropathy is a common complication of diabetic neuropathy. No treatments are known to be effective for progressive pain and sensory loss associated with diabetic neuropathy. Alternative effective treatment strategies have been sought.

OBJECTIVES

To systematically review the evidence from randomized controlled trials concerning the role of decompressive surgery of lower limbs for symmetrical diabetic peripheral neuropathy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Trials Register (May 2006), CENTRAL (The Cochrane Library, Issue 2 2006), MEDLINE from (January 1966 to August 2006), EMBASE (from January 1980 to August 2006), LILACS (from January 1982 to August 2006), and CINAHL (from January 1982 to August 2006).

SELECTION CRITERIA

We included all randomized or quasi-randomized controlled human trials in which any form of decompressive surgery of the lower limbs nerves had been used to treat diabetic symmetrical distal polyneuropathy (DSDP) compared with no treatment or medical therapy. Patients with DSDP were included if they had decompression (with or without neurolysis) of at least two of the following nerves in both lower limbs, for the treatment of DSDP: the posterior tibial nerve (including calcaneal, medial and lateral plantar nerves), deep peroneal nerve at the ankle, common peroneal nerve at the knee, lateral femoral cutaneous nerve and sural nerves in the posterior calf region. The primary outcome measure was the change in pain measured by the visual analogue scale (VAS) between the baseline and a follow-up period of greater than three months.

DATA COLLECTION AND ANALYSIS

We identified 142 publications from the above search strategies. The three authors of this manuscript reviewed abstracts of all papers independently. Only eight of these were considered relevant to the question at hand. The data from these 8 studies were entered onto standardized data extraction forms. We planned to use Review Manager to pool the results from appropriate studies comparing the same treatments; dichotomous outcomes to obtain pooled relative risks (RR); measured outcomes to obtain pooled weighted mean differences; and a fixed-effect analysis unless there was evidence of serious heterogeneity between studies sufficient to justify the use of random-effects analysis.

MAIN RESULTS

This review failed to identify a single randomized controlled trial or any other well designed prospective study controlling for the non-operated limb that showed improvements in pre defined end points after decompressive surgery.

AUTHORS' CONCLUSIONS

The results of this review suggest that the role of decompressive surgery for diabetic symmetric distal neuropathy is unproven.

Diabetic neuropathy: the painful foot

Diabetic neuropathy typically present as a mixture of sensory, motor and autonomic involvement. The development and severity of the neuropathy varies. This article briefly reviews the types of diabetic neuropathy and their relationship to pain and discusses the proposed etiologies.

Focal and multifocal neuropathies

The focal and multifocal neuropathies affect only a minority of patients with diabetes; however, they form a major clinical problem in terms of diagnosis, development of significant symptoms and signs, and often inadequate therapy. Diagnosis requires accurate and detailed clinical history and neurologic examination combined with targeted neurophysiologic tests, which differ considerably from those carried out in day-to-day practice. Because of their relatively infrequent occurrence, treatment is not evidence based.

Diabetic neuropathies: features and mechanisms

Diabetic neuropathies include both focal neuropathies and diffuse polyneuropathy. Polyneuropathy, the most common of the diabetic neuropathies excluding focal entrapment, has not yet been explained by a single disease mechanism despite intensive investigation. A number of abnormalities appear to cascade into a 'vicious cycle' of progressive microvascular disease associated with motor, sensory and autonomic fiber loss. These abnormalities include excessive polyol (sugar alcohol) flux through the aldose reductase pathway, functional and structural alterations of nerve microvessels, nerve and ganglia hypoxia, oxidative stress, nonspecific glycosylation of axon and microvessel proteins, and impairment in the elaboration of trophic factors critical for peripheral nerves and their ganglia. While an initiating role for nerve ischemia in the development of polyneuropathy has been proposed, the evidence for it can be questioned. The role of sensory and autonomic ganglia in the development of polyneuropathy has had relatively less attention despite the possibility that they may be vulnerable to a variety of insults, particularly neurotrophin deficiency. Superimposed on the deficits of polyneuropathy is the failure of diabetic nerves to regenerate as effectively as nondiabetics. Polyneuropathy has not yet yielded to specific forms of treatment but a variety of new trials addressing plausible hypotheses have been initiated. This review will summarize some of the clinical, pathological and experimental work applied toward understanding human diabetic neuropathy and will emphasize ideas on pathogenesis.

Phrenic neuropathy in association with diabetes

We report the case of a 51-year-old man who presented with breathlessness on exertion and orthopnoea in association with Type 2 diabetes mellitus. Investigation showed bilateral diaphragmatic paralysis due to phrenic neuropathy. There was no evidence of neuropathy or microvascular disease elsewhere. Phrenic neuropathy may be an important, albeit rare, complication of diabetes and diaphragmatic function should be considered in any patient with unexplained breathlessness and orthopnoea.

Mild ischemia causes severe pathological changes in experimental diabetic nerve

Nerve ischemia is considered one of etiological factors in the development of structural changes in peripheral nerves associated with diabetes mellitus. To assess the effect of mild ischemia on diabetic nerve, a subthreshold dose of polystyrene microspheres was injected intraarterially to occlude microvessels of the sciatic nerve and its branches in 20-week streptozotocin-induced diabetic and control rats. Diabetic sciatic and tibial nerves showed severe pathological change of myelinated fibers, whereas nondiabetic nerves were normal or had minor structural abnormalities. Morphometrical evaluation confirmed a greater frequency of abnormal myelinated fibers in diabetic nerves especially in central fascicular regions. The results indicate that diabetic nerve has an increased morphological susceptibility to nerve ischemia. Endoneurial hypoxia, which may result from hemorheological and vascular abnormalities, is likely to cause a lowered threshold to ischemic tolerance in diabetic nerve. This increased vulnerability to ischemia may render diabetic nerve unduly susceptible to hyperglycemia-induced systemic tissue abnormalities.

Conditions associated with carpal tunnel syndrome

With use of a comprehensive medical records-linkage system, we identified the comorbid conditions and risk factors in the residents of Rochester, Minnesota, who had a diagnosis of carpal tunnel syndrome during 1961 through 1980. In 43.2% of the 1,016 patients, no associated conditions were found on review of the medical records, whereas associated conditions were documented in 56.8%. The most frequent of these conditions were Colles' fracture, rheumatoid arthritis, hormonal agents or oophorectomy (or both), diabetes mellitus, and, among men, occupations that involved excessive use of the hands. Rheumatoid arthritis, diabetes mellitus, and pregnancy were significantly more frequent among the study patients with carpal tunnel syndrome than in the general population of Rochester, Minnesota. The standardized morbidity ratio was 3.6 for rheumatoid arthritis, 2.3 for diabetes mellitus, and 2.5 for pregnancy. The population attributable risk for pregnancy among women 15 to 44 years old was 7.0%. The standardized morbidity ratio for polymyalgia rheumatica was not significantly increased.

Structural alterations of nerve during cuff compression

Whether compression nerve injury is due to ischemia, direct mechanical injury, or both remains unsettled. To assess structural changes of nerve during compression, peroneal nerves of rats were compressed at various pressures for different times, and the structural alterations were stopped by simultaneous in situ and perfusion fixation. The structural changes observed during a few minutes of compression cannot be explained by ischemic injury because the pathologic alterations characteristic of ischemia take many hours to develop and in any case are different from the ones found here. The pressure- and time-related structural changes observed in the present study under the cuff were (i) decrease in fascicular area and increase in fiber density due to expression of endoneurial fluid; (ii) compression and expression of axoplasm, sometimes to the point of fiber transection; (iii) lengthening of internodes; and (iv) obscuration of nodes of Ranvier due to cleavage and displacement of myelin and overlapping of nodes by displaced loops of myelin. At the edges of the cuff the changes were (i) increase of fascicular area probably from expressed endoneurial fluid; (ii) widening of nodal gaps, perhaps mainly from translocated axonal fluid; and (iii) disordered structure of axoplasm. We suggest that the process of paranodal demyelination and axonal transection are linked, occur during the act of compression, and are due to shear forces. The initial event is expression of endoneurial fluid, followed by compression and expression of axoplasm and cleavage and displacement of layers of myelin. Conceivably, with prolonged cuff compression ischemic injury might be found to be superimposed on mechanical injury.