The spatial distribution of fiber loss in diabetic polyneuropathy suggests ischemia

The effect of sensory nerve stimulation on sensory nerve function in people with peripheral neuropathy associated with diabetes

OBJECTIVE

To assess the effect of sensory nerve stimulation in older people with peripheral neuropathy associated with diabetes (DPN).

MATERIALS AND METHODS

A randomized, placebo controlled, double blind trial was used to assess the effect of 12 weeks of low frequency sensory nerve stimulation (LF-SNS) in the lower limb [International Patent Application No. PCT/AU2004/001079: 'nerve function and tissue healing' (Z. Khalil)]. Response to capsaicin, basal microvascular blood flow, electric cutaneous threshold and oxygen tension were assessed pre- and post-treatment and between limbs.

PARTICIPANTS

People 55 years of age or older diagnosed with DPN: 35 active and 31 placebo participants.

RESULTS

Between groups comparisons: no significant differences occurred between stimulation groups. Within subject comparisons: in the active LF-SNS group, comparing stimulated to contralateral legs, there were significant increases in size of capsaicin flare [t(1,33)=3.65, p<0.05] and capillary blood flow [t(1,34)=-0.33, p<0.05]. There was a trend to improvement in time to initial flare response [t(1,34)=-1.86, p=0.07]. No changes were evident in the placebo group. RESPONDER ANALYSES: In a group of 'responders', the time to initial flare response (p<0.05, r=0.64), size of capsaicin flare (p<0.05 r=1.0) and microvascular blood flow (p<0.05, r=0.60) improved significantly after LF-SNS.

CONCLUSIONS

The observed data suggest that LF-SNS improves nerve function in a subset of people with DPN. Targeting toward probably 'responders' may deliver the greatest benefit from short-term therapy. Testing optimal application in others seems warranted.

Diabetic neuropathy part 1: overview and symmetric phenotypes

Diabetes is the most common cause of neuropathy in United States and neuropathies are the most common complication of diabetes mellitus, affecting up to 50% of patients with type 1 and type 2 diabetes mellitus. Symptoms usually include numbness, tingling, pain, and weakness. Dizziness with postural changes can be seen with autonomic neuropathy. Metabolic, vascular, and immune theories have been proposed for the pathogenesis of diabetic neuropathy. Axonal damage and segmental demyelination can be seen with diabetic neuropathies. Management of diabetic neuropathy should begin at the initial diagnosis of diabetes and mainly requires tight and stable glycemic control.

Impaired neurovascular repair in subjects with diabetes following experimental intracutaneous axotomy

Diabetic complications and vascular disease are closely intertwined. Diabetes mellitus is a well-established risk factor for both large and small vessel vascular changes, and conversely other vascular risk factors confer increased risk for diabetic complications such as peripheral neuropathy, nephropathy and retinopathy. Furthermore, axons and blood vessels share molecular signals for purposes of navigation, regeneration and terminal arborizations. We examined blood vessel, Schwann cell and axonal regeneration using validated axotomy models to study and compare patterns and the relationship of regeneration among these different structures. Ten subjects with diabetes mellitus complicated by neuropathy and 10 healthy controls underwent 3 mm distal thigh punch skin biopsies to create an intracutaneous excision axotomy followed by a concentric 4-mm overlapping biopsy at different time points. Serial sections were immunostained against a pan-axonal marker (PGP9.5), an axonal regenerative marker (GAP43), Schwann cells (p75) and blood vessels (CD31) to visualize regenerating structures in the dermis and epidermis. The regenerative and collateral axonal sprouting rates, blood vessel growth rate and Schwann cell density were quantified using established stereology techniques. Subjects also underwent a chemical 'axotomy' through the topical application of capsaicin, and regenerative sprouting was assessed by the return of intraepidermal nerve fibre density through regenerative regrowth. In the healed 3 mm biopsy sites, collateral and dermal regenerative axonal sprouts grew into the central denervated area in a stereotypic pattern with collateral sprouts growing along the dermal-epidermal junction while regenerative dermal axons, blood vessels and Schwann cells grew from their transected proximal stumps into the deep dermis. Vessel growth preceded axon and Schwann cell migration into the denervated region, perhaps acting as scaffolding for axon and Schwann cell growth. In control subjects, Schwann cell growth was more robust and extended into the superficial dermis, while among subjects with diabetes mellitus, Schwann tubes appeared atrophic and were limited to the mid-dermis. Rates of collateral (P=0.0001), dermal axonal regenerative sprouting (P=0.02), Schwann cell migration (P<0.05) and blood vessel growth (P=0.002) were slower among subjects with diabetes mellitus compared with control subjects. Regenerative deficits are a common theme in diabetes mellitus and may underlie the development of neuropathy. We observed that blood vessel growth recapitulated the pattern seen in ontogeny and preceded regenerating nerve fibres, suggesting that enhancement of blood vessel growth might facilitate axonal regeneration. These models are useful tools for the efficient investigation of neurotrophic and regenerative drugs, and also to explore factors that may differentially affect axonal regeneration.

Proximal neuropathic lesions in distal symmetric diabetic polyneuropathy: findings of high-resolution magnetic resonance neurography

OBJECTIVE

This study investigated high-resolution magnetic resonance neurography (MRN) in distal symmetric diabetic polyneuropathy (dPNP).

RESEARCH DESIGN AND METHODS

MRN comprised high-resolution transaxial imaging of peripheral nerves of the lower limbs in 20 patients with type 2 diabetes (10 with dPNP, type 2/dPNP[+], and 10 without dPNP, type 2/dPNP[-]), seven patients with type 1 diabetes (two with dPNP, type 1/dPNP[+], five without dPNP, type 1/dPNP[-]), and 10 nondiabetic control subjects. Intraneural T2 lesions, as the main diagnostic criterion of MRN, were detected visually by two independent observers and quantitatively by analysis of T2 contrast ratios.

RESULTS

Multifocal fascicular, symmetric intraneural T2 lesions occurred in the proximal trunks of sciatic nerves in four patients (three with type 2/dPNP[+] and one with type 1/dPNP[+]) but not in control subjects (type 2/dPNP[-], type 1/dPNP[-], nondiabetic control subjects), which was confirmed by quantitative analysis. Clinical severity was higher in patients with T2 lesions (neuropathy deficit score: 10 vs. 7.8; P = 0.05).

CONCLUSIONS

For the first time, proximal neuropathic lesions of dPNP are reported in vivo. This supports that accumulation of proximal, multifocal fascicular injury may be important in disease progression.

The impact of diabetes on the outcomes of surgical and nonsurgical treatment of patients in the spine patient outcomes research trial

STUDY DESIGN

A secondary analysis comparing diabetic patients with nondiabetic patients enrolled in the Spine Patient Outcomes Research Trial (SPORT).

OBJECTIVE

To compare surgical outcomes and complications between diabetic and nondiabetic spine patients.

SUMMARY OF BACKGROUND DATA

Patients with diabetes are predisposed to comorbidities that may confound the diagnosis and treatment of patients with spinal disorders.

METHODS

Baseline characteristics and outcomes of 199 patients with diabetes were compared with those of the nondiabetic population in a total of 2405 patients enrolled in the Spine Patient Outcomes Research Trial for the diagnoses of intervertebral disc herniation (IDH), spinal stenosis (SpS), and degenerative spondylolisthesis (DS). Primary outcome measures include the 36-Item Short Form Health Survey (SF-36) Health Status questionnaire and the Oswestry Disability Index.

RESULTS

Patients with diabetes were significantly older and had a higher body mass index than nondiabetic patients. Comorbidities, including hypertension, stroke, cardiovascular disease, and joint disease, were significantly more frequent in diabetic patients than in nondiabetic patients. Patients with diabetes and IDH did not make significant gains in pain and function with surgical intervention relative to diabetic patients who underwent nonoperative treatment. Diabetic patients with SpS and DS experienced significantly greater improvements in pain and function with surgical intervention when compared with nonoperative treatment. Among those who had surgery, nondiabetic patients with SpS achieved marginally significantly greater gains in function than their diabetic counterparts (SF-36 physical function, P = 0.062). Among patients who had surgery for DS, diabetic patients did not have as much improvement in pain or function as did the nondiabetic population (SF-36 bodily pain, P = 0.003; physical function, P = 0.002). Postoperative complications were more prevalent in patients with diabetes than in nondiabetic patients with SpS (P = 0.002). There was an increase in postoperative (P = 0.028) and intraoperative (P = 0.029) blood replacement in DS patients with diabetes.

CONCLUSION

Diabetic patients with SpS and DS benefited from surgery, though older SpS patients with diabetes have more postoperative complications. IDH patients with diabetes did not benefit from surgical intervention.

Cardiovascular dementia - a different perspective

The number of dementia patients has been growing in recent years and dementia represents a significant threat to aging people all over the world. Recent research has shown that the number of people affected by Alzheimer's disease (AD) and dementia is growing at an epidemic pace. The rapidly increasing financial and personal costs will affect the world's economies, health care systems, and many families. Researchers are now exploring a possible connection among AD, vascular dementia (VD), diabetes mellitus (type 2, T2DM) and cardiovascular diseases (CD). This correlation may be due to a strong association of cardiovascular risk factors with AD and VD, suggesting that these diseases share some biologic pathways. Since heart failure is associated with an increased risk of AD and VD, keeping the heart healthy may prove to keep the brain healthy as well. The risk for dementia is especially high when diabetes mellitus is comorbid with severe systolic hypertension or heart disease. In addition, the degree of coronary artery disease (CAD) is independently associated with cardinal neuropathological lesions of AD. Thus, the contribution of T2DM and CD to AD and VD implies that cardiovascular therapies may prove useful in preventing AD and dementia.

Characteristics of lower extremity pressure sensation impairment in developing diabetic sensory polyneuropathy

The medical literature presents diabetic sensory polyneuropathy as a length-dependent process producing a stocking distribution of sensory loss in the lower extremities. If a purely length-dependent etiology for diabetic sensory polyneuropathy were true, then a validated comparison of sensory loss at any equidistant site about the forefoot will reveal findings consistent with the accepted stocking pattern of anesthesia. A single-blinded, age-matched, control/experimental study is made into the frequency of apparent purely length-dependent A-beta fiber pathology in developing diabetic sensory polyneuropathy. Control (n = 46) and experimental (n = 83) central US subjects are examined with a subjective neuropathy screening questionnaire, vibratory threshold, and single-point pressure threshold testing. There is a plantar predominant pattern (61.5%) of sensory loss in developing diabetic sensory polyneuropathy, even after adjusting for sensitivity differences between different areas of the foot. A typical stocking pattern of sensory loss was not found. Although axonal pathology is length dependent, it is not apparently a purely length-dependent process. Therefore, a purely metabolic explanation for sensory loss is unlikely. In addition, an anatomic component for A-beta fiber pathology is implied by this study.

Extracellular matrix remodelling in human diabetic neuropathy

The extracellular matrix of peripheral nerve plays a vital role in terms of normal nerve fibre function and also in the regenerative response following nerve injury. Nerve fibre loss is a major feature of diabetic neuropathy; however, the regenerative response is limited and this may be associated with changes in the composition of the extracellular matrix. Glycoproteins and collagens are major components of the extracellular matrix and are known to be important in terms of axonal growth. This work has therefore examined whether changes in the expression of two major glycoproteins, laminin and tenascin, and three collagen types (IV, V and VI) occur in the endoneurial and perineurial connective tissue compartments of human diabetic nerve. Despite being known to have a positive effect in terms of axonal growth, laminin levels were not elevated in the diabetic nerves. However, the pattern of tenascin expression did differ between the two groups being found in association with axon myelin units in the diabetic samples only. The pattern of collagen IV expression was the same in both tissue groups and was not found to be up-regulated. However, levels of collagen V and VI were both significantly increased in the endoneurium and for collagen VI also in the perineurium.

Compartmentalized microfluidic culture platform to study mechanism of paclitaxel-induced axonal degeneration

Chemotherapy induced peripheral neuropathy is a common and dose-limiting side effect of anticancer drugs. Studies aimed at understanding the underlying mechanism of neurotoxicity of chemotherapeutic drugs have been hampered by lack of suitable culture systems that can differentiate between neuronal cell body, axon or associated glial cells. Here, we have developed an in vitro compartmentalized microfluidic culture system to examine the site of toxicity of chemotherapeutic drugs. To test the culture platform, we used paclitaxel, a widely used anticancer drug for breast cancer, because it causes sensory polyneuropathy in a large proportion of patients and there is no effective treatment. In previous in vitro studies, paclitaxel induced distal axonal degeneration but it was unclear if this was due to direct toxicity on the axon or a consequence of toxicity on the neuronal cell body. Using microfluidic channels that allow compartmentalized culturing of neurons and axons, we demonstrate that the axons are much more susceptible to toxic effects of paclitaxel. When paclitaxel was applied to the axonal side, there was clear degeneration of axons; but when paclitaxel was applied to the soma side, there was no change in axon length. Furthermore, we show that recombinant human erythropoietin, which had been shown to be neuroprotective against paclitaxel neurotoxicity, provides neuroprotection whether it is applied to the cell body or the axons directly. This observation has implications for development of neuroprotective drugs for chemotherapy induced peripheral neuropathies as dorsal root ganglia do not possess blood-nerve-barrier, eliminating one of the cardinal requirements of drug development for the nervous system. This compartmentalized microfluidic culture system can be used for studies aimed at understanding axon degeneration, neuroprotection and development of the nervous system.

Characteristics of lower extremity pressure sensation impairment in developing diabetic sensory polyneuropathy

The medical literature presents diabetic sensory polyneuropathy as a length-dependent process producing a stocking distribution of sensory loss in the lower extremities. If a purely length-dependent etiology for diabetic sensory polyneuropathy were true, then a validated comparison of sensory loss at any equidistant site about the forefoot will reveal findings consistent with the accepted stocking pattern of anesthesia. A single-blinded, age-matched, control/experimental study is made into the frequency of apparent purely length-dependent A-beta fiber pathology in developing diabetic sensory polyneuropathy. Control (n = 46) and experimental (n = 83) central US subjects are examined with a subjective neuropathy screening questionnaire, vibratory threshold, and single-point pressure threshold testing. There is a plantar predominant pattern (61.5%) of sensory loss in developing diabetic sensory polyneuropathy, even after adjusting for sensitivity differences between different areas of the foot. A typical stocking pattern of sensory loss was not found. Although axonal pathology is length dependent, it is not apparently a purely length-dependent process. Therefore, a purely metabolic explanation for sensory loss is unlikely. In addition, an anatomic component for A-beta fiber pathology is implied by this study.

Cutaneous sensibility and peripheral nerve function in patients with unmedicated essential hypertension

Sensorimotor deficits in patients with essential hypertension may be due to impaired nerve function. Cutaneous sensory thresholds, median nerve sensory and motor conduction velocities, and median nerve sensory action potential amplitudes were assessed in 30 patients with unmedicated essential hypertension and 29 normotensives. Cutaneous sensory thresholds were higher and sensory action potential amplitudes smaller in hypertensives than normotensives whereas sensory and motor nerve conduction velocities did not differ between groups. These data suggest that hypertension may reduce the number of active sensory nerve fibers without affecting myelination. Sensory action potential amplitudes were inversely related to cutaneous sensory thresholds, suggesting that subclinical axonal neuropathy of sensory afferents may help account for perceptual deficits that characterize hypertension.

Diabetes mellitus and the peripheral nervous system: manifestations and mechanisms

Diabetes targets the peripheral nervous system with several different patterns of damage and several mechanisms of disease. Diabetic polyneuropathy (DPN) is a common disorder involving a large proportion of diabetic patients, yet its pathophysiology is controversial. Mechanisms considered have included polyol flux, microangiopathy, oxidative stress, abnormal signaling from advanced glycation endproducts and growth factor deficiency. Although some clinical trials have demonstrated modest benefits in disease stabilization or pain therapy in DPN, robust therapy capable of reversing the disease is unavailable. In this review, general aspects of DPN and other diabetic neuropathies are examined, including a summary of recent therapeutic trials. A particular emphasis is placed on the evidence that the neurobiology of DPN reflects a unique yet common and disabling neurodegenerative disorder.

Early diabetic neuropathy: Triggers and mechanisms

Peripheral neuropathy, and specifically distal peripheral neuropathy (DPN), is one of the most frequent and troublesome complications of diabetes mellitus. It is the major reason for morbidity and mortality among diabetic patients. It is also frequently associated with debilitating pain. Unfortunately, our knowledge of the natural history and pathogenesis of this disease remains limited. For a long time hyperglycemia was viewed as a major, if not the sole factor, responsible for all symptomatic presentations of DPN. Multiple clinical observations and animal studies supported this view. The control of blood glucose as an obligatory step of therapy to delay or reverse DPN is no longer an arguable issue. However, while supporting evidence for the glycemic hypothesis has accumulated, multiple controversies accumulated as well. It is obvious now that DPN cannot be fully understood without considering factors besides hyperglycemia. Some symptoms of DPN may develop with little, if any, correlation with the glycemic status of a patient. It is also clear that identification of these putative non-glycemic mechanisms of DPN is of utmost importance for our understanding of failures with existing treatments and for the development of new approaches for diagnosis and therapy of DPN. In this work we will review the strengths and weaknesses of the glycemic hypothesis, focusing on clinical and animal data and on the pathogenesis of early stages and triggers of DPN other than hyperglycemia.

Ultrastructural anatomy of the renal nerves in rats

The innervation within mammalian kidneys (intrinsic innervation) has been extensively described in the literature, particularly for rats. In contrast, there is still a lack of detailed description of the morphology of the extrinsic renal nerves leading to the kidney. The aim of the present study was to describe, in detail, the morphology of the renal nerves in rats. Left renal nerves were evaluated in 6 normal adult Wistar rats. After nerve recordings, in order to ascertain that the nerves studied were the extrinsic renal nerves, rats were killed and the nerves prepared for transmission electron microscopy. Morphometry was carried out with the aid of computer software. The total numbers of myelinated and unmyelinated fibers were 22+/-6 and 1246+/-110, respectively, with a ratio of unmyelinated/myelinated fiber of 109+/-26. The diameters of myelinated fibers showed an unimodal distribution with a peak at 3.0 microm but more than 17% of the fibers showed diameters larger than 5 microm. Unmyelinated fiber distribution was unimodal, with peak between 0.5 and 0.7 microm. The present study adds new information on the morphology of renal nerves in rats and provides morphological basis for further studies involving the structural basis of altered renal responses in conditions such as hypertension, ageing, diabetes and peripheral neuropathies.

Altered nerve excitability properties in established diabetic neuropathy

The underlying cause of diabetic neuropathy remains unclear, although pathological studies have suggested an ischaemic basis related to microangiopathy, possibly mediated through effects on the energy-dependent Na+/K+ pump. To investigate the pathophysiology of diabetic neuropathy, axonal excitability techniques were undertaken in 20 diabetic patients with neuropathy severity graded through a combination of quantitative sensory testing (QST) using a vibratory stimulus, assessment of symptom severity using the Total Neuropathy Symptom Score (T-NSS) and measurement of glycosylated haemoglobin as a marker of disease control. To assess axonal excitability, compound muscle action potentials were recorded at rest from abductor pollicis brevis following stimulation of the median nerve, and stimulus-response behaviour, threshold electrotonus, a current-threshold relationship and the recovery of excitability were recorded in each patient. All patients had established neuropathy, with abnormalities of T-NSS present in all patients and QST abnormalities present in 65%. Compared with controls, diabetic neuropathy patients had significant reduction in maximal CMAP amplitude (P < 0.0005), accompanied by a 'fanning in' of threshold electrotonus. In addition, the strength-duration time constant was decreased in diabetic neuropathy patients and recovery cycles were altered with reductions in refractoriness, the duration of the relative refractory period, superexcitability and subexcitability. It is proposed that while the changes in threshold electrotonus with supportive findings in the current-threshold relationship are consistent with axonal depolarization, possibly mediated by a decrease in Na+/K+ pump activity, the alterations in the recovery cycle of excitability could be explained on the basis of a smaller action potential, reflecting a limitation on the nodal driving current imposed by a reduction in Na+ conductances.

Diabetic Neuropathies

Diabetes mellitus is associated with a wide spectrum of neuropathy syndromes, ranging from a mild asymptomatic distal sensory neuropathy to a severe disabling radiculoplexus neuropathy. As the pathophysiology of these separate conditions is better understood, classification of the various phenotypes becomes important because of treatment implications. Here we provide a short summary of the history of the classification of diabetic neuropathies and try to describe the most common forms classified according to their presumed pathophysiology. We have tried to include epidemiological data where available, as well as histopathology of nerve in several diabetic neuropathies.

The acute effects of glycemic control on nerve conduction in human diabetics

OBJECTIVE

To investigate acute changes in nerve conduction associated with glycemic control. In diabetes, nerve dysfunction can result from reversible metabolic factors associated with hyperglycemia, as well as structural changes.

METHODS

Multiple nerve conduction parameters including F-wave latencies were measured in 47 diabetic patients with prominent hyperglycemia before and after intensive insulin treatment.

RESULTS

Four weeks after the start of treatment, there was a significant improvement in minimal F-wave latencies of the median (P<0.001) and tibial (P<0.001) nerves, and in distal latencies (P=0.01) and sensory nerve conduction velocities (P<0.001) of the median nerves. Amplitudes of motor and sensory responses did not change significantly. These findings were similar for patients with type 1 (n=8) and those with type 2 (n=39) diabetes. Patients with poorer glycemic control or milder neuropathy tended to show greater changes after treatment.

CONCLUSIONS

Glycemic control quickly alters the speed of nerve conduction. F-wave latencies and conduction times across the carpal tunnel are very sensitive parameters.

SIGNIFICANCE

Serial nerve conduction studies can detect reversible slowing of nerve conduction presumably caused by metabolic factors, such as decreased Na+/K+-ATPase activity, the altered polyol pathway, and tissue acidosis.

Diabetic autonomic neuropathy: evidence for apoptosis in situ in the rat

We examined the hypothesis that activation of the apoptosis cascade occurs relatively early in diabetes mellitus affecting three distinct neuronal populations that are involved in regulating gut function: (i) dorsal root ganglion (DRG), (ii) vagus nodose ganglion and (iii) colon myenteric plexus. A validated streptozotocin-induced diabetic rat model and age-matched healthy controls were studied. After 4-8 weeks of diabetes the animals were anaesthetized, fixed in situ and the relevant tissues removed. After 1 month of diabetes some animals were treated with insulin for 2 weeks to restore euglycaemia. Apoptosis was measured using immunohistochemical detection of activated caspase-3 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL)-positive cells in adjacent sections in neurones (PGP 9.5-positive cells). The level of apoptosis was confirmed using double-label assessment of caspase-3 and TUNEL in DRG preparations. Caspase-3 immunoreactive neurones demonstrated a range in staining intensity. When all grades of staining were included, 6-8% of the DRG, nodose ganglia and myenteric neurones were immunoreactive in the preparations from diabetic rats compared with 0.2-0.5% in controls. Neurones staining positive for both caspase-3 and TUNEL accounted for 1-2% of the total neuronal population in all three preparations in diabetic rats compared with 0.1-0.2% in controls (P < 0.05). Insulin treatment reversed the percentage of TUNEL-positive neurones in diabetic rats to control levels. Activation of the apoptosis cascade occurs relatively early in diabetic autonomic neuropathy and may contribute to the pathophysiology of this disorder.

Perineurial cell basement membrane thickening and myelinated nerve fibre loss in diabetic and nondiabetic peripheral nerve

Diabetic neuropathy is associated with changes in the extracellular matrix of the perineurium, including thickening of the basement membrane of the perineurial cells. Peripheral vascular disease (PVD) is a common vascular condition that can occur in the absence or presence of diabetes. Thickening of the vascular basement membrane of the vasa nervorum is associated with both diabetes and nondiabetic peripheral vascular disease. However, perineurial cell basement membrane (PCBM) thickening in the nondiabetic PVD state has not, until now, been investigated. In this study, 36 nerve fascicles were examined from three patient groups: a diabetic group, a nondiabetic PVD group, and a group free of both PVD and diabetes (control group). PCBM thickness, fascicle size, and myelinated nerve fibre (MNF) density were measured in all three groups. Endoneurial blood vessels were also observed for evidence of morphological changes. The results showed that the thickness of the PCBM is significantly greater in the diabetic group in comparison with both the control and the nondiabetic PVD group, and this increase in thickness is linearly related to fascicle size. The thickness of the PCBM was not significantly different between the nondiabetic PVD and control groups. Although both the nondiabetic PVD and diabetic groups showed a loss of myelinated nerve fibres in comparison with the control group, this loss was statistically greater in the diabetic group. The endoneurial blood vessels of both the diabetic and nondiabetic PVD groups showed evidence of endothelial cell hyperplasia, hypertrophy, and basement membrane reduplication.

Nerve and ganglion blood flow in diabetes: an appraisal

Vasa nervorum, the vascular supply to peripheral nerve trunks, and their associated cell bodies in ganglia have unique anatomical and physiological characteristics. Several different experimental approaches toward understanding the changes in vase nervorum following injury and disease have been used. Quantative techniques most widely employed have been microelectrode hydrogen clearance palarography and [14C]iodoantipyrine autoradiographic distribution, whereas estimates of red blood cell flux using a fiber-optic laser Doppler probe offer real time data at different sites along the nerve trunk. There are important caveats about the use of these techniques, their advantages, and their limitations. Reports of nerve blood flow require careful documentation of physiological variables, including mean arterial pressure and nerve temperature during the recordings. Several ischemic models of the peripheral nerve trunk have addressed the ischemic threshold below which axonal degeneration ensues (< 5ml/100 g/min). Following injury, rises in local blood flow reflect acitons of vasoactive peptides, nitric oxide, and the development of angiogenesis. In experimental diabetes, a large number of studies have documented reductions in nerve blood flow and tandem corrections of nerve blood flow and conduction slowing. A significant proportions, however, of the work can be criticized on the basis of methodology and interpretation. Similarly, not all work has confirmed that reductions of nerve blood flow are an invariable feature of experimental or human diabetic polyneuropathy. Therefore, while there is disagreement as to whether early declines in nerve blood flow "account" for diabetic polyneuropathy, there is unquestioned eveidence of early microangiopathy. Abnormalities of vase nervorum and micorvessels supplying ganglia at the very least develop parallel to and together with changes in neurons, Schwann cells, and axons.

Role of the Schwann cell in diabetic neuropathy

The relationships among Schwann cells, axons, and the perineurial barrier emphasize the key role Schwann cells play in normal functions of the nerve. Schwann cells are responsible for action potential velocity through insulation of axons, maintenance of axonal caliber, and correct localization of Na+ channels; immunological and funcitonal integrity of the nerve through the perineurial blood-nerve-barrier; and effective nerve regeneration. In diabetic neuropathy, many of these facets of nerve function are defective. Hypoxia, hyerglycemia, and increased oxidative stress contribute directly and indirectly to Schwann cell dysfunction. The results include impaired paranodal barrier function, damaged myelin, reduced antioxidative capacity, and decreased neurotrophic support for axons. This chapter discusses the role of the Schwann cell in the normal or regenerating nerve nad in the altered metabolic conditons of diabetes.

Autonomic neuropathy in streptozotocin diabetic rats: effect of acetyl-L-carnitine

The present study was designed to characterize cardiac autonomic neuropathy in streptozotocin-induced (45 mg/kg i.v.) diabetic rat by analysis of heart rate variability (HRV), and to assess, in this model, the effects of treatment with acetyl-L-carnitine (ALC). Heart rate was reduced in diabetic rats (332+/-22 vs. 411+/-35 beat per min; P<0.0001). This bradycardia was partly reversed with ALC (369+/-52 beat per min; P<0.05 vs. untreated). Both time- and frequency-domain parameters of HRV were significantly reduced in diabetic rats. The reduction of spectral power was around 50% at high frequencies and about 70% at low frequencies, suggesting a decrease of parasympathetic activity. Low/high frequency ratio was significantly decreased in diabetic rats suggesting decreased sympathetic tone, while nonlinear analysis indicated a reduction of the chaotic complexity of heart rate dynamics in diabetic rats. Standard deviation of heart rate in ALC-treated rats was significantly higher than in untreated diabetic rats (P<0.0001). ALC counteracts the reduction of the power spectrum observed in diabetic animals (P<0.0005) normalizing the spectra profile. ALC restored chaotic complexity of heart rate dynamics. These results on the whole indicate that both sympathetic and parasympathetic cardiac tone were reduced significantly in diabetic rats and that ALC treatment prevents the development of autonomic neuropathy in streptozotocin-induced diabetes in rats.

Accuracy of sampling methods in morphometric studies of human sural nerves

The aim of this study was to ascertain the minimum sample required to accurately measure the total number of myelinated fibres, mean myelinated fibre density (MFD), myelinated fibre diameter (Ds) and axonal diameter (Da) in morphometric studies of sural nerve biopsies. Measurements were obtained by sampling a single fascicle or systematic sampling of up to 50% of the total transverse fascicular area of two control and eighteen pathological sural nerves showing varying degrees of demyelination and axonal degeneration. MFD and fibre size were heterogeneous between fascicles in both control and pathological sural nerves, and morphometric results from one fascicle and systematic sampling of up to 50% of the total transverse fascicular area did not accurately represent the whole myelinated fibre population in the sural nerve. For accurate morphometric data it is necessary to quantitate all the myelinated fibres in the sural nerve.

Automated and representative fascicle selection for computer-assisted morphometry of myelinated nerve fibres in peripheral nerves

We describe an algorithm that permits representative fascicle selection for sample acquisition from the entire cross-section of a nerve. We calculate the number of fascicles necessary for the acquisition of a given sample volume of nerve fibres from the image magnification, determine the scheme of intrafascicular sampling, and measure the (estimated) nerve fibre density. We start by storing the positions of all fascicles as coordinates of the microscope motor stage. We then recruit the needed fascicles from the file by calling them up out of the storage order with a constant interval, using the quotient of the total number of fascicles and the number of fascicles necessary to obtain the sample size for this purpose. The results obtained on the analysis of 40 specimens of sural and tibial nerves by means of the image analysis system IBAS are reported.

Electrophysiological changes in diabetic neuropathy: from subclinical alterations to disabling abnormalities

Clinical spectrum of diabetic neuropathy is variable; it may be asymptomatic, but once established as polyneuropathy, it is irreversible and may finally be disabling. To estimate the prevalence of subclinical diabetic polyneuropathy in the UAE, we undertook a pilot study by means of nerve conduction study (NCS) of peroneal motor and sural sensory studies in 60 diabetics with no symptoms of neuropathy. Neurological examination revealed clinical abnormalities suggesting polyneuropathy in 26 patients, 43% of the patients. NCS revealed abnormal values in 63% of the whole patients. Abnormal NCS was confirmed in 88% of the positive sign group. As to the negative sign group 44% had abnormalities in NCS. Prolonged F-wave latency was seen in 29% in no sign group and in 66% of the patients with positive signs. We found close association between neurological deficit score and abnormalities in NCS. Among various parameter of systemic nerve conduction study in subclinical patients, prolonged F-wave latency seems the commonest abnormality suggesting morphological changes in subclinical diabetic nerve. Decrease in amplitude of compound sensory action potential of sural nerve is another earlier abnormality, which is, then, accompanied by a fall in motor amplitude of peroneal nerve in advanced patients. Recently, our own group of Hirosaki has demonstrated that somatosensory central conduction time (CCT) between the spinal cord entry time and the arrival time to the sensory cortex is prolonged in diabetics. This abnormality might be partly responsible for the irreversible sensory deficits of diabetic neuropathy.

New trends in the etiopathogenesis of diabetic peripheral neuropathy

Neuropathy is well recognized as a major complication of insulin-dependent diabetes mellitus in adults, resulting in significant morbidity and possibly an increased mortality. Both the peripheral and autonomic nervous systems can be involved, and adolescents with diabetes can show early evidence of neuropathy. The pathogenesis of diabetic neuropathy remains unclear but is thought to involve various mechanisms. This complication can be traced to the metabolic effects of hyperglycemia and/or other effects of insulin deficiency on the various constituents of the peripheral nerve. The polyol pathway and/or nonenzymatic glycation affecting one or more cell types in the multicellular constituents of the peripheral nerve appear likely to have an inciting role. The role of other factors, such as possible direct neurotrophic effects of insulin and insulin-related growth factors, seems to be relevant.

The role of protein kinase C in the development of the complications of diabetes

Diabetes mellitus produces a state of chronic hyperglycemia which in turn leads to the development of severe complications including retinopathy, nephropathy, neuropathy, and atherosclerosis. Many different mechanisms have been put forward to attempt to explain how glucose elevations can damage these various organ systems. Protein kinase C activation is one of the sequelae of hyperglycemia and is thought to play a role in the development of diabetic complications. There are multiple mechanisms for its activation in the diabetic state and multiple downstream effects attributable to that activation. The role of protein kinase C activation in the development of the above-mentioned complications of diabetes is discussed in this chapter. In addition, the potential use of isoform-specific inhibitors of protein kinase C for the treatment of diabetic complications is proposed.

Possible impact of genetic differences on the development of neuropathic pain-like behaviors after unilateral sciatic nerve ischemic injury in rats

The development of neuropathic-like behaviors following unilateral ischemic injury to the sciatic nerve was examined and compared in four rat strains: Sprague--Dawley (SD), Wistar--Kyoto (WK), spontaneously hypertensive (SHR) and Dark--Agouti (DA). We have also compared two sub-strains of SD rats supplied from two different vendors (SD-BK and SD-DK). The responses to mechanical, heat or cold stimuli of both hind paws were measured before and regularly after injury for up to 10 weeks. Spontaneous paw lifting and changes in paw posture after nerve injury were also examined. Significant differences in basal sensitivity to mechanical or heat stimulation were seen among the four rat strain studied with SHR and DA rats being less sensitive than the SD and WK rats. All strains of rats developed bilateral mechanical allodynia and ipsilateral heat hyperalgesia after photochemically-induced nerve ischemia, but the time-course and magnitude of the responses were significantly different among the strains. Again, the SHR and DA were found to be least susceptible to the development of abnormal pain-like responses. Cold allodynia occurred only in WK and SD-BK. SD-DK rats on the other hand developed more severe mechanical allodynia than SD-BK. SHR and DA rats showed less deficits in paw posture after nerve injury whereas spontaneous pain lifting, a measure of possible spontaneous pain, was comparable among all strains. Light microscopic study of the injured sciatic nerve showed comparable nerve damage in SHR, WK and two sub-strains of SD rats. The DA rats however exhibited reduced area of intraneural damage. Finally, electronmicroscopic examination revealed that damage to both myelinated and unmyelinated fibers occurred in this model in all strains. These results showed that normal sensitivity and the development of pain-like response after partial nerve injury differ substantially among different strains of rats, supporting the emerging concept that genetic factors affect pain sensitivity under normal conditions and after nerve injury. The apparent resistance of DA rats to nerve ischemia, however, may suggest that genetic factors not directly related to pain modulation also play a role in the diverse outcomes. Our results indicate that sub-strains of rats also showed variable development of neuropathic pain-like behaviors to both the modality and magnitude of the effect. Thus, controlling sub-strains is also important in experimental studies of neuropathic pain in rats.

Cilostazol prevents impairment of slow axonal transport in streptozotocin-diabetic rats

We studied the effects of cilostazol, an antiplatelet and vasodilating agent, on axonal transport patterns of cytoskeletal proteins in the motor fibers of sciatic nerve of streptozotocin-induced diabetic rats. Proteins labeled with L-[35S]methionine in 6-mm consecutive segments of the nerve were analyzed electrophoretically following fractionation into Triton-soluble and-insoluble subpopulations. Transport rates of proteins (particularly neurofilaments) in slow component a were reduced by 50% 2 weeks after labeling (4 weeks after streptozotocin). An apparent reduction of tubulin and actin was observed at later intervals after induction of diabetes. Actin transported in slow component b was also impaired, though to a lesser extent than in component a. Cilostazol prevented transport impairment of both slow components a and b without affecting hyperglycemia or reduction in body weight gain. These results suggest that in sciatic motor fibers early defects in slowly transported proteins are more marked in slow component a, and that impairment may be caused primarily by hemodynamic abnormalities.

Diabetic neuropathy--a continuing enigma

In this article we will review the clinical signs and symptoms of diabetic somatic polyneuropathy (DPN), its prevalence and clinical management. Staging and classification of DPN will be exemplified by various staging paradigms of varied sophistication. The results of therapeutic clinical trials will be summarized. The pathogenesis of diabetic neuropathy reviews an extremely complex issue that is still not fully understood. Various recent advances in the understanding of the disease will be discussed, particularly with respect to the differences between neuropathy in the two major types of diabetes. The neuropathology and natural history of diabetic neuropathy will be discussed pointing out the heterogeneities of the disease. Finally, the various prospective therapeutic avenues will be dealt with and discussed.

Effects of 15-month aldose reductase inhibition with fidarestat on the experimental diabetic neuropathy in rats

We examined the effects of long-term treatment with an aldose reductase inhibitor (ARI) fidarestat on functional, morphological and metabolic changes in the peripheral nerve of 15-month diabetic rats induced by streptozotocin (STZ). Slowed F-wave, motor nerve and sensory nerve conduction velocities were corrected dose-dependently in fidarestat-treated diabetic rats. Morphometric analysis of myelinated fibers demonstrated that frequencies of abnormal fibers such as paranodal demyelination and axonal degeneration were reduced to the extent of normal levels by fidarestat-treatment. Axonal atrophy, distorted axon circularity and reduction of myelin sheath thickness were also inhibited. These effects were associated with normalization of increased levels of sorbitol and fructose and decreased level of myo-inositol in the peripheral nerve by fidarestat. Thus, the results demonstrated that long-term treatment with fidarestat substantially inhibited the functional and structural progression of diabetic neuropathy with inhibition of increased polyol pathway flux in diabetic rats.

Peripheral and central conduction abnormalities in diabetes mellitus

OBJECTIVES

To investigate peripheral and central somatosensory conduction in patients with diabetes.

METHODS

The authors recorded sensory nerve action potentials and 5-channel somatosensory evoked potentials (SEPs) with noncephalic reference after median nerve stimulation in 55 patients with diabetes and 41 age- and height-matched normal subjects. The authors determined onset or peak latencies of the Erb's potential (N9) and the spinal N13-P13 and the cortical N20-P20 components, and obtained the central conduction time (CCT) by onset-to-onset and peak-to-peak measurements.

RESULTS

Both onset and peak latencies of all SEP components were prolonged in patients with diabetes. The mean onset CCT in the diabetic group was 6.3 +/- 0.5 msec (mean +/- SD)-significantly longer than that in the control group (6.1 +/- 0.2 msec)-whereas no significant difference was found in the peak CCT. The amplitudes of N9 and N13-P13 components (but not N20-P20) were significantly smaller in the diabetic group. The peripheral sensory conduction velocity was also decreased in the diabetic group, but there was no significant correlation between peripheral conduction slowing and the onset of CCT prolongation.

CONCLUSIONS

Diabetes affects conductive function in the central as well as peripheral somatosensory pathways. The CCT abnormality does not coincide with lowering of the peripheral sensory conduction. The current results do not favor a hypothesis that a central-peripheral distal axonopathy plays an important role in development of diabetic polyneuropathy.

Nitric oxide involvement in the trigeminal hyperalgesia in diabetic rats

Trigeminal hyperalgesia frequently appears in diabetic neuralgia altering the transmission of orofacial sensory information. This study was designed to explore the effects of trigeminal hyperalgesia in streptozotocin-induced diabetes monitoring the expression of nitric oxide synthase in the trigeminal ganglion cells. The threshold to heat noxious stimuli decreased in diabetic animals. The number of NADPH-diaphorase (NADPH-d)-positive neurons significantly decreased in the diabetic rats compared with controls. Insulin treatment prevented the decreased nociceptive threshold and reduction of the number of NADPH-d-positive neurons. These findings point out that there is a relationship between the trigeminal nociceptive perception and NADPH-d neuronal expression suggesting that NO may play a role in the pathogenesis of trigeminal sensory neuropathy.

Development of a mouse model of neuropathic pain following photochemically induced ischemia in the sciatic nerve

A mouse model of neuropathic pain was developed by a photochemically induced ischemic nerve injury in normal male C57/BL6 mice. The ischemia was induced by unilateral irradiation of the sciatic nerve with an argon ion laser after intravenous administration of a photosensitizing dye, erythrosin B. The nerve injury resulted in a significant decrease in withdrawal threshold of the hindpaws to mechanical stimulation with von Frey hairs, as well as increased responsiveness to cold and heat stimulation. The mice, however, did not exhibit overt spontaneous pain-like behaviors. The evoked pain-related behaviors were observed bilaterally, although the ipsilateral changes were greater than on the contralateral side. The extent and time course of the behavioral changes were related to the duration of laser irradiation, with 1-min exposure producing the most consistent effect. Morphological examination at the light microscopic level revealed partial demyelination and axonal degeneration of the large myelinated fibers at the epicenter of the lesion 1 week postirradiation. The extent of the damage was correlated with the duration of irradiation. Injury and loss of unmyelinated fibers were also observed at the electronmicroscopic level. We conclude that an intravascular photochemical reaction leading to ischemia results in graded damage to the sciatic nerve in mice. Moreover, the nerve injury is associated with the development of abnormal pain-related behaviors. Both the behavioral and the morphological changes are correlated with the duration of irradiation. These results establish a mouse model of partial nerve injury with neuropathic pain-like behaviors which may be useful in studies using genetically modified mice.

Diabetic Neuropathies

There are currently no treatments available (beyond optimal control of hyperglycemia) that arrest or reverse progressive diabetic polyneuropathy. Consultation with a diabetologist is indicated for patients with poorly controlled disease and polyneuropathy. Immunotherapy for diabetic lumbosacral plexopathy has been advocated but is not supported to date by class 1 clinical trial evidence. Pharmacologic treatment for painful neuropathy may include topical anesthetics, capsaicin cream, anticonvulsants, tricyclic antidepressants, mexiletine, and opioids. Gabapentin, a newer anticonvulsant, has an attractive side-effect profile (a consideration in older patients) and has fewer interactions with other drugs. Amitriptyline may cause excessive sedation, postural hypotension, constipation, and urinary retention, but low evening doses (10 to 25 mg), slowly titrated upward, may offer relief from nocturnal pain. Opioids should not be withheld from patients with severe pain or with intolerance of or contraindications to other agents. A single physician should supervise their use.

Diabetic peripheral nerves are susceptible to multifocal ischemic damage from endothelin

Experimental diabetes is associated with susceptibility to ischemic fiber damage. In a model of ischemia previously studied in our laboratory and induced by topical endothelin-1 (ET-1), diabetic nerves had selective conduction block that progressed to motor fiber inexcitability, associated with prolonged vasoconstrictive ischemia. In this work, we report our analysis of histological consequences of ET-1 ischemia. Our hypothesis was that intense epineurial vasoconstriction would be associated with centrofascicular fiber loss, confined to diabetic nerves. By quantitating the sectorial and fascicular distribution of fibers undergoing axonal degeneration we determined the degree and geographical distribution of axonal damage induced by topical ET-1 in the sciatic nerve trunk two weeks after ischemia. Axonal damage induced by ET-1 in diabetics exceeded that of non-diabetics by a factor greater than 5. The pattern of axonal degeneration was multifocal but not centrofascicular and did not vary with fascicular area. Some small fascicles had rates of axonal degeneration that far exceeded those of large adjacent fascicles. In other instances, sectors with intense axonal degeneration were subperineurial crescentic areas, similar to those originally described by Nukada following microsphere embolization. We conclude that diabetic nerves are highly susceptible to ischemic injury, but that multifocal and not centrofascicular fiber degeneration may be encountered.

Impaired ascendant central pathways conduction in impotent diabetic subjects

OBJECTIVES

Diabetic impotence is generally due to peripheral neuropathy, but a central pathway impairment has also been suggested. We evaluated somatosensory transmission in a group of impotent diabetic men to assess the role of central nervous system (CNS) involvement.

MATERIALS AND METHODS

Somatosensory evoked potentials (SEPs) of pudendal (pdn) and posterior tibial (ptn) nerves were recorded in 74 patients. Type and duration of diabetes, severity of sexual dysfunction, medium term metabolic control, occurrence of microangiopathic chronic complications and autonomic neuropathy were evaluated.

RESULTS

Our data show an impairment of central conduction times in pdn (25.7%) and ptn (39.2%) greater than peripheral nervous impairment (pdn 12.2%, ptn 8.1%), in impotent diabetic patients without any further major complication. Central nervous conduction delay resulted to be correlated with poor glycemic control. Significant evident autonomic dysfunction was found only in a minority of cases.

CONCLUSION

Our data might suggest that altered conduction along CNS and somatic peripheral neuropathy might develop independently. We confirm the hypothesis of a "central diabetic neuropathy" and suggest that central sensory pathways involvement, not related to peripheral impairment, could play a role in the pathogenesis of erectile dysfunction in diabetic patients.

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.

Risks for sensorimotor peripheral neuropathy and autonomic neuropathy in non-insulin-dependent diabetes mellitus (NIDDM)

Identification of risk factors for development of diabetic sensorimotor peripheral neuropathy (DSPN) and diabetic autonomic neuropathy (DNA) may help to prevent or modify these complications. The ABCD Trial, a prospective study of diabetic complications, has identified risk factors of the presence and staging of peripheral neuropathy based on neurological symptom scores, neurological disability scores, autonomic function testing and quantitative sensory examination. DSPN is independently associated with diabetes duration [odds ratio (OR) = 1.5 per 10 years], body weight (OR = 1.1 per 5 kg), age (OR = 1.8 per 10 years), retinopathy (OR = 2.3), overt albuminuria (OR = 2.5), height (OR = 1.2 per 10 cm), duration of hypertension (OR = 1.1 per 10 years), insulin use (OR = 1.4), and race/ethnicity [African American vs. non-Hispanic white (OR = 0.4) and Hispanic vs. non-Hispanic white (OR = 0.8)]. DAN is independently associated with diabetes duration (OR = 1.2 per 10 years), body weight (OR = 1.1 per 5 kg), glycosylated hemoglobin (OR = 1.1 per 2.5%), overt albuminuria (OR = 1.6), and retinopathy (OR = 1.8).

Effects of dietary supplementation with arachidonic acid rich oils on nerve conduction and blood flow in streptozotocin-diabetic rats

Diabetes mellitus is associated with defective essential fatty acid desaturation. In experimental models this contributes to characteristic reductions in peripheral nerve conduction velocity (NCV) and blood flow, which may be corrected by dietary supplementation with gamma-linolenic acid (GLA) rich oils to bypass the delta-6 desaturation deficit. There is debate about the mechanism of this improvement, including whether it depends on synthesis of series 1 prostanoids derived from di-homo GLA or series 2 prostanoids from arachidonic acid (ARA). The aim was to assess the efficacy of two ARA-rich (approximately 39% content) oils in correcting neurovascular dysfunction in streptozotocin-induced diabetic rats. After 6 weeks of untreated diabetes, rats were treated for a further 2 weeks with 1% dietary oil supplements before assessment of sciatic motor NCV and endoneurial blood flow. NCV was 19% reduced in diabetic rats and this was largely (approximately 86%) corrected by both oil treatments. A 48% deficit in endoneurial nutritive blood flow with diabetes was approximately 70% reversed by the two oils, vascular conductance being in the non-diabetic range. Thus, nerve conduction and perfusion deficits in diabetic rats are corrected by ARA-rich oil treatment. The magnitudes of these changes were similar to expectations based on previous studies of GLA-rich oils, therefore it is likely that the neurovascular effect of increased synthesis of series 2 prostanoids makes a major contribution to the beneficial action of n-6 essential fatty acids in experimental diabetic neuropathy.

Chronic inflammatory demyelinating polyneuropathy (CIDP) in diabetics

Seven diabetic patients developed a progressive, moderately severe, motor rather than sensory neuropathy predominantly affecting the legs. This met clinical and electrophysiological criteria for chronic inflammatory demyelinating polyneuropathy (CIDP). Nerve biopsies showed a variety of abnormalities, none of which clearly distinguished between diabetic polyneuropathy and CIDP. The patients were treated with combinations of corticosteroids, azathioprine, plasmapheresis and intravenous immune globulin; all improved substantially. We believe that CIDP may masquerade as unusually severe and progressive diabetic distal symmetric polyneuropathy. It is important to recognize CIDP in diabetics because, unlike diabetic polyneuropathy, CIDP is treatable.

Comparison of the effects of ascorbyl gamma-linolenic acid and gamma-linolenic acid in the correction of neurovascular deficits in diabetic rats

Essential fatty acid metabolism is impaired by diabetes mellitus and gamma-linolenic acid rich treatments such as evening primrose oil correct deficits in nerve conduction and endoneurial blood flow in diabetic rats. Other mechanistically unrelated treatments, such as antioxidants and aldose reductase inhibitors have a similar effect and there may be positive interactions with multiple treatments. Our aim was to compare the efficacy of a novel essential fatty acid derivative, ascorbyl gamma-linolenic acid, with that of gamma-linolenic acid in correcting diabetic neurovascular deficits. Eight weeks of diabetes caused 20.4 and 48.2% reductions in sciatic motor conduction velocity and nutritive endoneurial blood flow, respectively. Treatment was given for the last 2 weeks with gamma-linolenic acid (100 mg.kg-1.day-1) either in pure form or as ascorbyl gamma-linolenic acid, an equivalent dose of ascorbate (21 mg.kg-1.day-1) or jointly with ascorbate and gamma-linolenic acid. Conduction velocity was corrected by 39.8, 87.4, 13.2 and 66.8% with gamma-linolenic acid, ascorbyl gamma-linolenic acid, ascorbate and gamma-linolenic acid plus ascorbate, respectively. Corresponding ameliorations of the nutritive blood flow deficit were 44.0, 87.4, 87.4, 13.2 and 65.7%. For the gamma-linolenic acid plus ascorbate combinatin, and especially for ascorbyl gamma-linolenic acid, the magnitude of correction for conduction velocity and blood flow was greater than expected for simple addition of ascorbate and gamma-linolenic acid, indicating a synergistic interaction. Thus, with an efficacy 40 times that of evening primrose oil in rats, ascorbyl gamma-linolenic acid may be a suitable candidate for clinical trials of diabetic neuropathy.

Nodal Na(+)-channel displacement is associated with nerve-conduction slowing in the chronically diabetic BB/W rat: prevention by aldose reductase inhibition

Chronic nerve conduction showing in experimental diabetic neuropathy has been associated with decreased nodal Na+ permeability and an ultrastructurally identifiable loss of axo-glial junctions, which comprise the paranodal voltage channel barrier separating nodal Na+ channels from paranodal K+ channels. In human and experimental diabetic neuropathy these structural changes of the paranodal apparatus correlate closely with the nerve conduction defect. The present immunocytochemical study of the alpha-subunit of the Na+ channel examined whether the breach of the voltage channel barrier may account for a shift in the distribution of Na+ channels explaining decreased nodal Na+ permeability. Biobreeding Wistar (BB/W) rats diabetic for 4-8 months showed a progressive redistribution of nodal Na+ channels across the paranodal barrier into the paranodal and internodal domains which was associated with chronic nerve conduction slowing. The present data suggest that structural damage to the paranodal barrier system in diabetic nerve facilitates the lateral displacement of Na+ channels from the nodal axolemma thereby diminishing their nodal density and the nodal Na+ permeability associated with the chronic nerve conduction defect in experimental diabetes. These abnormalities were prevented by the treatment with an aldose reductase inhibitor, belonging to a class of drugs that, in neuropathic patients, improves nerve-conduction velocity and repairs axo-glial dysjunction of the paranodal apparatus.

Nerve fiber regeneration following axotomy in the diabetic biobreeding Worcester rat: the effect of ARI treatment

Diabetic neuropathy is characterized by progressive nerve fiber degeneration resulting in nerve fiber loss. In order to examine what role impaired nerve fiber regeneration may play in the progressive net nerve fiber loss, spontaneously diabetic biobreeding Worcester (BB/W) rats were subjected to sciatic nerve axotomy at 6 weeks of diabetes. Myelinated nerve fiber regeneration was examined morphologically and morphometrically at various time points following axotomy. The data were compared with those of axotomized control rats and diabetic rats treated with an aldose reductase inhibitor (ARI) from 1 week after onset of diabetes. Diabetic rats showed a significant attenuation of nerve fiber regeneration during the first 6 weeks following axotomy, which was normalized at 4 months postaxotomy. ARI treatment resulted in an initial burst of supranormal regeneration, which was normalized at 4 months postaxotomy. Impaired nerve fiber regeneration in diabetic rats was associated with a marked delay in preceding Wallerian degeneration and decreased phagocytic activity by macrophages, changes not demonstrated in ARI-treated diabetic rats. We propose that the impaired nerve fiber regeneration in the diabetic BB/W rat may, in part, be the result of impaired recruitment and/or function of macrophages necessary for the initiation of normal nerve fiber regeneration. The corrective effects of ARI treatment on the regenerative ability of diabetic peripheral nerve suggest that an activated polyol pathway may impact on both intrinsic and extrinsic mechanisms governing nerve fiber regeneration.

Diabetes and the nervous system

Hyperglycemia and its vascular complications affect the entire nervous system, contributing to increased morbidity and mortality. Chronic hyperglycemia is not only a known and major risk factor for cerebral vascular diseases but also the presence of hyperglycemia at the time of a cerebrovascular event may adversely influence the outcome. It also affects the treatment of some neurodegenerative disorders, and there are suggestions that diabetes may in fact suffer from a "chronic diabetic encephalopathy." Its varied effects on the peripheral nervous system result in several forms of diabetic neuropathies, the exact pathogenesis of which is still obscure. There is, however, some new information that may link metabolic and vascular hypotheses.