Arterio-venous shunting and proliferating new vessels in acute painful neuropathy of rapid glycaemic control (insulin neuritis)

Glycemic variability's impact on painful diabetic peripheral neuropathy in type 2 diabetes patients

Hyperglycemia in type 2 diabetes leads to diabetic peripheral neuropathy (DPN) and neuropathic pain, yet the association between glycemic variability and painful DPN remains insufficiently evidenced. To address this, we conducted a prospective longitudinal cohort study involving adult type 2 diabetes patients at a medical center. DPN was identified using the Michigan Neuropathy Screening Instrument (MNSI), and neuropathic pain was assessed with the Taiwan version of the Douleur Neuropathique 4 (DN4-T) questionnaire. At baseline in 2013, all participants were free of DPN and were re-evaluated in 2019 for the development of painful DPN. We measured visit-to-visit glycemic fluctuations using the coefficient of variation (CV) of fasting plasma glucose (FPG) and glycated hemoglobin (HbA1c). Patients were stratified into tertiles according to their FPG-CV and HbA1c-CV. Among the 622 participants, 267 developed DPN during the six-year follow-up. Following matching of age and sex, 210 patients without DPN and 210 with DPN (including 26 with neuropathic pain) were identified. Our findings revealed a significant association between high FPG-CV and painful DPN, with the highest tertile showing an adjusted odds ratio of 2.82 (95% confidence interval 1.04-7.64) compared to the lowest tertile. On the contrary, HbA1c-CV did not show a significant association with the risk of painful DPN. Our study indicates that higher FPG-CV is associated with an increased risk of painful DPN, supporting the role of glycemic variability in the development of painful DPN.

Diabetic Neuropathy: An Overview of Molecular Pathways and Protective Mechanisms of Phytobioactives

Diabetic neuropathy (DN) is a common and debilitating complication of diabetes mellitus that affects the peripheral nerves and causes pain, numbness, and impaired function. The pathogenesis of DN involves multiple molecular mechanisms, such as oxidative stress, inflammation, and pathways of advanced glycation end products, polyol, hexosamine, and protein kinase C. Phytochemicals are natural compounds derived from plants that have various biological activities and therapeutic potential. Flavonoids, terpenes, alkaloids, stilbenes, and tannins are some of the phytochemicals that have been identified as having protective potential for diabetic neuropathy. These compounds can modulate various cellular pathways involved in the development and progression of neuropathy, including reducing oxidative stress and inflammation and promoting nerve growth and repair. In this review, the current evidence on the effects of phytochemicals on DN by focusing on five major classes, flavonoids, terpenes, alkaloids, stilbenes, and tannins, are summarized. This compilation also discusses the possible molecular targets of numerous pathways of DN that these phytochemicals modulate. These phytochemicals may offer a promising alternative or complementary approach to conventional drugs for DN management by modulating multiple pathological pathways and restoring nerve function.

Impact of Intensive Glycemic Treatment on Diabetes Complications-A Systematic Review

Diabetes complications can be related to the long duration of the disease or chronic hyperglycemia. The follow-up of diabetic patients is based on the control of chronic hyperglycemia, although this correction, if obtained rapidly in people living with severe chronic hyperglycemia, can paradoxically interfere with the disease or even induce complications. We reviewed the literature describing the impact of the rapid and intense treatment of hyperglycemia on diabetic complications. The literature review showed that worsening complications occurred significantly in diabetic microangiopathy with the onset of specific neuropathy induced by the correction of diabetes. The results for macroangiopathy were somewhat mixed with the intensive and rapid correction of chronic hyperglycemia having a neutral impact on stroke and myocardial infarction but a significant increase in cardiovascular mortality. The management of diabetes has now entered a new era with new therapeutic molecules, such as gliflozin for patients living with type 2 diabetes, or hybrid insulin delivery systems for patients with insulin-treated diabetes. Our manuscript provides evidence in support of these personalized and progressive algorithms for the control of chronic hyperglycemia.

Impact of the Rapid Normalization of Chronic Hyperglycemia on the Receptor Activator of Nuclear Factor-Kappa B Ligand and the Osteoprotegerin System in Patients Living with Type 2 Diabetes: RANKL-GLYC Study

The RANKL-GLYC study aims to explore the impact of the rapid correction of chronic hyperglycemia on the receptor activator of nuclear factor-kappa B ligand (RANKL) and its antagonist osteoprotegerin (OPG). RANKL and OPG are considered the main factors in the pathophysiology of Charcot neuroarthropathy, a devastating complication of the joints that remains poorly understood. The study began recruiting patients in September 2021 and ends in June 2022; the final study results are scheduled for January 2023.

Nerve and Vascular Biomarkers in Skin Biopsies Differentiate Painful From Painless Peripheral Neuropathy in Type 2 Diabetes

Painful diabetic peripheral neuropathy can be intractable with a major impact, yet the underlying pain mechanisms remain uncertain. A range of neuronal and vascular biomarkers was investigated in painful diabetic peripheral neuropathy (painful-DPN) and painless-DPN and used to differentiate painful-DPN from painless-DPN. Skin biopsies were collected from 61 patients with type 2 diabetes (T2D), and 19 healthy volunteers (HV). All subjects underwent detailed clinical and neurophysiological assessments. Based on the neuropathy composite score of the lower limbs [NIS(LL)] plus seven tests, the T2D subjects were subsequently divided into three groups: painful-DPN (n = 23), painless-DPN (n = 19), and No-DPN (n = 19). All subjects underwent punch skin biopsy, and immunohistochemistry used to quantify total intraepidermal nerve fibers (IENF) with protein gene product 9.5 (PGP9.5), regenerating nerve fibers with growth-associated protein 43 (GAP43), peptidergic nerve fibers with calcitonin gene-related peptide (CGRP), and blood vessels with von Willebrand Factor (vWF). The results showed that IENF density was severely decreased (p < 0.001) in both DPN groups, with no differences for PGP9.5, GAP43, CGRP, or GAP43/PGP9.5 ratios. There was a significant increase in blood vessel (vWF) density in painless-DPN and No-DPN groups compared to the HV group, but this was markedly greater in the painful-DPN group, and significantly higher than in the painless-DPN group (p < 0.0001). The ratio of sub-epidermal nerve fiber (SENF) density of CGRP:vWF showed a significant decrease in painful-DPN vs. painless-DPN (p = 0.014). In patients with T2D with advanced DPN, increased dermal vasculature and its ratio to nociceptors may differentiate painful-DPN from painless-DPN. We hypothesized that hypoxia-induced increase of blood vessels, which secrete algogenic substances including nerve growth factor (NGF), may expose their associated nociceptor fibers to a relative excess of algogens, thus leading to painful-DPN.

The Treatment of Painful Diabetic Neuropathy

Painful diabetic peripheral neuropathy (painful-DPN) is a highly prevalent and disabling condition, affecting up to one-third of patients with diabetes. This condition can have a profound impact resulting in a poor quality of life, disruption of employment, impaired sleep, and poor mental health with an excess of depression and anxiety. The management of painful-DPN poses a great challenge. Unfortunately, currently there are no Food and Drug Administration (USA) approved disease-modifying treatments for diabetic peripheral neuropathy (DPN) as trials of putative pathogenetic treatments have failed at phase 3 clinical trial stage. Therefore, the focus of managing painful- DPN other than improving glycaemic control and cardiovascular risk factor modification is treating symptoms. The recommended treatments based on expert international consensus for painful- DPN have remained essentially unchanged for the last decade. Both the serotonin re-uptake inhibitor (SNRI) duloxetine and α2δ ligand pregabalin have the most robust evidence for treating painful-DPN. The weak opioids (e.g. tapentadol and tramadol, both of which have an SNRI effect), tricyclic antidepressants such as amitriptyline and α2δ ligand gabapentin are also widely recommended and prescribed agents. Opioids (except tramadol and tapentadol), should be prescribed with caution in view of the lack of definitive data surrounding efficacy, concerns surrounding addiction and adverse events. Recently, emerging therapies have gained local licenses, including the α2δ ligand mirogabalin (Japan) and the high dose 8% capsaicin patch (FDA and Europe). The management of refractory painful-DPN is difficult; specialist pain services may offer off-label therapies (e.g. botulinum toxin, intravenous lidocaine and spinal cord stimulation), although there is limited clinical trial evidence supporting their use. Additionally, despite combination therapy being commonly used clinically, there is little evidence supporting this practise. There is a need for further clinical trials to assess novel therapeutic agents, optimal combination therapy and existing agents to determine which are the most effective for the treatment of painful-DPN. This article reviews the evidence for the treatment of painful-DPN, including emerging treatment strategies such as novel compounds and stratification of patients according to individual characteristics (e.g. pain phenotype, neuroimaging and genotype) to improve treatment responses.

Are the Protean Effects of Pentoxifylline in the Therapy of Diabetes and Its Complications Still Relevant?

Pentoxifylline (Px) has protean effects that can be utilized in the therapy of diabetes and its complications. There have been well-documented but often inconclusive improvements in peripheral arterial disease, foot ulcers, peripheral neuropathy, nephropathy, retinopathy, ischemic heart disease and cerebrovascular disease. In addition, non-alcoholic steatosis and steatohepatitis, which are closely associated with insulin resistance and type 2 diabetes, have been shown to improve with pentoxifylline. Surprisingly, pentoxifylline modestly improves insulin resistance through improvements in capillary blood flow as well as beta cell function and decreased hepatic glucose production. The therapeutic effects of pentoxifylline are complementary to the effects of drugs such as blockers of the renin-angiotensin-aldosterone system when utilized in the therapy of diabetic nephropathy.

Pathogenesis, diagnosis and clinical management of diabetic sensorimotor peripheral neuropathy

Diabetic sensorimotor peripheral neuropathy (DSPN) is a serious complication of diabetes mellitus and is associated with increased mortality, lower-limb amputations and distressing painful neuropathic symptoms (painful DSPN). Our understanding of the pathophysiology of the disease has largely been derived from animal models, which have identified key potential mechanisms. However, effective therapies in preclinical models have not translated into clinical trials and we have no universally accepted disease-modifying treatments. Moreover, the condition is generally diagnosed late when irreversible nerve damage has already taken place. Innovative point-of-care devices have great potential to enable the early diagnosis of DSPN when the condition might be more amenable to treatment. The management of painful DSPN remains less than optimal; however, studies suggest that a mechanism-based approach might offer an enhanced benefit in certain pain phenotypes. The management of patients with DSPN involves the control of individualized cardiometabolic targets, a multidisciplinary approach aimed at the prevention and management of foot complications, and the timely diagnosis and management of neuropathic pain. Here, we discuss the latest advances in the mechanisms of DSPN and painful DSPN, originating both from the periphery and the central nervous system, as well as the emerging diagnostics and treatments.

Alpha 1 adrenoceptor expression in skin, nerves and blood vessels of patients with painful diabetic neuropathy

Diabetic neuropathy (dNP) patients often suffer from severe neuropathic pain. It was suggested that alpha-1 adrenoceptor (α₁-AR) hyperresponsiveness contributes to pain in dNP. The aim of our study was to quantify α₁-AR expression using immunohistochemistry in skin biopsies of nine patients with painful diabetic neuropathy compared to 10 healthy controls. Additionally, the association between α₁-AR expression and activation with spontaneous and sympathetically maintained pain (SMP) induced by intradermal injection of the α₁-agonist phenylephrine was investigated. For control purposes the α₂-agonist clonidine was injected in a different session. We found that dermal nerve density was significantly lower in dNP than in controls. However, α₁-AR expression was significantly greater on cutaneous blood vessels and keratinocytes of dNP patients than controls. A similar trend, which failed to reach significance, was observed for dermal nerves. Intradermal injection of phenylephrine induced only minor pain, which resolved after a few minutes. Adrenergically evoked pain persisted for more than 15 min in only one patient, but none of the patients fulfilled the criteria for SMP (pain increase after injection of phenylephrine and decrease after clonidine). In conclusion, our results imply that SMP does not occur in dNP. However, elevated expression of α₁-AR on keratinocytes and dermal blood vessels is an important finding, since this could contribute to dNP progression and supports the theory of receptor up-regulation of denervated structures. The implications of this α₁-upregulation should be examined in further studies.

Spectrum of diabetic neuropathies

The diabetic state results in neuropathy. The main causative mechanism is hyperglycemia, although microvascular involvement, hypertriglyceridemia, as well as genetic and immune mechanisms may be contributory. There is a growing spectrum of types of diabetic neuropathies that differ based on the type of fibers involved (e.g. myelinated, unmyelinated, autonomic, somatic), distribution of nerves involved, and mechanisms of neuropathy. The most common type is distal sensory neuropathy (DSN), which affects the distal ends of large myelinated fibers, more often sensory than motor, and is often asymptomatic. The next-most common is distal small fiber neuropathy (DSFN), which largely affects the unmyelinated fibers and carries the phenotype of burning feet syndrome. Diabetic autonomic neuropathy (DAN) occurs when widespread involvement of autonomic unmyelinated fibers occurs, and patients can be incapacitated with orthostatic hypotension as well as neurogenic bladder and bowel involvement. Radiculoplexus diabetic neuropathy causes proximal weakness and pain, usually in the lower extremity, and has a combination of immune, inflammatory, and vascular mechanisms. The nerve roots and plexus are involved. These patients present with proximal weakness of a subacute onset, often with severe pain and some autonomic failure. Finally, rapid and sustained reduction of blood glucose can result in treatment-induced diabetic neuropathy (TIND), which largely affects the sensory and autonomic fibers. This occurs if HbA1c is rapidly reduced within 3 months, and the likelihood is proportional to the original A1c and the size of the reduction.

Diabetic Neuropathy Collection: Treatment of Diabetic Neuropathy

Video: Treatment of Diabetic Neuropathy podcast recording (MP4 61908 kb).

Treatment induced neuropathy of diabetes

BACKGROUND

Treatment induced neuropathy of diabetes (TIND) is an iatrogenic painful sensory and autonomic neuropathy. Although the prevalence is not known, it is seen in up to 10% of tertiary cases referred for evaluation of diabetic neuropathy.

EVIDENCE

TIND is associated with a decrease in the glycosylated hemoglobin A1C in individuals with longstanding hyperglycemia. TIND is more common in individuals with type 1 diabetes, but can occur in anyone with diabetes through the use of insulin, oral hypoglycemic medications or diet control. There is an acute or subacute onset of neuropathy that is linked to the change in glucose control. Although the primary clinical manifestation is neuropathic pain there is a concurrent development of autonomic dysfunction, retinopathy and nephropathy.

CONCLUSION

TIND is more common than previously suspected. The number of cases reported over the past 10 years is much greater than historical literature predicted. Increased attention to target glucose control as a physician metric could suggest a possible explanation for the increased in TIND cases reported in recent years. At present, supportive care is the only recommended treatment. Future research is necessary to define the underlying mechanism, prevent development and to guide treatment recommendations.

Treatment-Induced Neuropathy of Diabetes (TIND) in Pediatrics: A Case Report and Review of the Literature

CONTEXT

Treatment-induced neuropathy of diabetes (TIND) is a rarely reported but important consideration in patients presenting with an acute onset of neuropathic symptoms following rapid correction of hyperglycemia in diabetes. Although it has been reported in children, the preponderance of literature focuses on adults with TIND.

CASE DESCRIPTION

We report an 18-year-old male with this condition and his clinical course. We then discuss the proposed pathophysiology of TIND and review the literature. We also provide a standard workup for the diagnosis of TIND.

CONCLUSION

In both pediatric and adult populations, TIND should be considered in diabetic patients who develop neuropathy acutely following rapid correction of hyperglycemia. Because the pathophysiology of TIND remains poorly understood, there is insufficient information regarding how to target susceptible individuals and prevent the development of TIND.

Sonographic assessment of nerve blood flow in diabetic neuropathy

AIMS

To undertake sonographic assessment of nerve blood flow in people with Type 2 diabetes and correlate the findings with neuropathy severity scores and electrophysiological measurements.

METHODS

Median and tibial nerve ultrasound scans were undertaken in 75 people with diabetes and 30 aged-matched controls without diabetes, using a high-resolution linear probe at non-entrapment sites. Nerve blood flow was quantified using power Doppler techniques to obtain the vessel score and the maximum perfusion intensity. Neuropathy severity was assessed using a total neuropathy score.

RESULTS

Diabetic nerves had higher rates of nerve blood flow detection (28%) compared to the control group (P < 0.0001). Significant correlations were found between nerve blood flow measurements and nerve size (P <0.001), reported sensory symptoms (P < 0.05) and neuropathy severity scores (P < 0.001). The cohort with diabetes had significantly larger median (8.5 ± 0.3 mm² vs 7.2 ± 0.1 mm² ; P < 0.05) and tibial nerves (18.0 ± 0.9 mm² vs 12.8 ± 0.5 mm² ; P < 0.05) compared with controls.

CONCLUSION

Peripheral nerve hypervascularity is detectable by ultrasonography in moderate to severe diabetic neuropathy with prominent sensory dysfunction.

The 2017 Banting Memorial Lecture The diabetic lower limb - a forty year journey: from clinical observation to clinical science

A series of clinical research projects conducted over the past 40 years, all of which were informed by clinical observation or discussions with people with diabetes and staff colleagues are described in this review. A study of necrobiosis lipoidica diabeticorum confirmed that this rare skin complication occurs predominantly in young women with Type 1 diabetes and other microvascular complications. Biopsies of necrobiotic lesions showed destruction of superficial nerve fibres by inflammatory tissue, which likely causes the sensory loss in lesions that is pathognomonic of the condition. The development of corneal confocal microscopy as a new non-invasive surrogate marker of peripheral neuropathy in diabetes is described next and several small studies of the use of this new technique in clinical research are reported. The influence of blood glucose instability on the genesis of neuropathic pain is then explained, with results suggesting that the stability of glycaemic control may be more important than the level of control achieved. Lastly, in neuropathy, studies of gustatory sweating are discussed, including the observation that sweating in the head and neck region is more common in people with end-stage diabetic nephropathy than in those with neuropathy. The disappearance of gustatory sweating after renal transplantation suggests a metabolic cause and for those with troublesome sweating, use of the anticholinergic, anti-muscarinic, topical cream glycopyrrolate is confirmed in a randomized control trial. In the area of diabetic foot research, distended dorsal foot veins were observed to be a clinical sign of sympathetic autonomic neuropathy: raised venous Po₂ and Doppler abnormalities of blood flow are highly suggestive of arteriovenous shunting. A series of studies of the abnormalities of pressures and loads under the neuropathic diabetic foot are described: high dynamic plantar pressures are highly predictive of subsequent ulceration in the neuropathic foot. Lastly, a number of recent studies on unsteadiness and gait abnormalities when climbing and descending stairs are described. It is hoped that the art of clinical observation survives in the highly technological 21st century.

Multifocal (tarsus and knee) activation of neuroarthropathy following rapid glycaemic correction

OBJECTIVE

To report a case of neuroarthropathy in the tarsus and knee following rapid glycaemic normalisation in a female patient with type I diabetes.

METHODS

A retrospective review of case notes.

RESULTS

We describe the case of a female patient with type I diabetes who had developed a multifocal neuroarthropathy in only six months, probably due to a rapid glycaemic normalisation. The onset of this neuroarthropathy was not only fast but mostly multifocal affecting two levels of joints.

CONCLUSION

The link between the onset of multifocal neuroarthropathy and the rapid correction of chronic hyperglycaemia is probably proven in our case. Patients with chronic hyperglycaemia with sensitive neuropathy should benefit from a gradual correction of their glycaemic imbalance in order to avoid the apparition of neuroarthropathy.

A case of treatment-induced neuropathy in an adolescent with type 1 diabetes

Treatment-induced neuropathy (TIN) in diabetes is an acute and painful yet completely reversible small fiber neuropathy precipitated by a rapid improvement in glycemic control. TIN is rare in children. A 16-year-old girl developed symmetrical painful neuropathy of the foot, autonomic neuropathy, and retinopathy 5 weeks after the diagnosis of type 1 diabetes. All causative workups were negative except for a drop-in hemoglobin A1c (HbA1c) from 17.4% to 7%, which fit with a diagnosis of TIN. Following symptomatic management, her neuropathy and retinopathy completely resolved in 2 months. Currently, she is 18 years old and doing well (HbA1c, 7.4%) without any recurrence of TIN. TIN should be suspected in any child presenting with recent-onset type 1 diabetes and acute onset neuropathy. Our case represents an unreported scenario of the rapid progression in TIN. Awareness among clinicians about this rare but completely reversible condition is necessary to ensure proper management and adherence to glycemic control.

Painful and Painless Diabetic Neuropathies: What Is the Difference?

PURPOSE OF REVIEW

The prevalence of diabetes mellitus and its chronic complications are increasing to epidemic proportions. This will unfortunately result in massive increases in diabetic distal symmetrical polyneuropathy (DPN) and its troublesome sequelae, including disabling neuropathic pain (painful-DPN), which affects around 25% of patients with diabetes. Why these patients develop neuropathic pain, while others with a similar degree of neuropathy do not, is not clearly understood. This review will look at recent advances that may shed some light on the differences between painful and painless-DPN.

RECENT FINDINGS

Gender, clinical pain phenotyping, serum biomarkers, brain imaging, genetics, and skin biopsy findings have been reported to differentiate painful- from painless-DPN. Painful-DPN seems to be associated with female gender and small fiber dysfunction. Moreover, recent brain imaging studies have found neuropathic pain signatures within the central nervous system; however, whether this is the cause or effect of the pain is yet to be determined. Further research is urgently required to develop our understanding of the pathogenesis of pain in DPN in order to develop new and effective mechanistic treatments for painful-DPN.

The association of diabetic microvascular and macrovascular disease with cutaneous circulation in patients with type 2 diabetes mellitus

AIMS

To study the impact of diabetic neuropathy, both peripheral sensorimotor (DPN) and cardiac autonomic neuropathy (CAN), on transcutaneous oxygen tension (TcPO₂) in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 163 participants were recruited; 100 with T2DM and 63 healthy individuals. Peripheral arterial disease (PAD) was defined as ankle-brachial index (ABI) values ≤0.90. Diagnosis of DPN was based on neuropathy symptom score and neuropathy disability score (NDS), while diagnosis of CAN on the battery of the cardiovascular autonomic function tests. TcPO₂ was measured using a TCM30 system.

RESULTS

Patients with T2DM had lower TcPO₂ levels when compared with healthy individuals. Among the diabetic cohort, those who had either PAD, DPN or CAN had significantly lower TcPO₂ values than participants without these complications. Multivariate linear regression analysis, after controlling for diabetes duration, diastolic blood pressure, HbA1c, albumin to creatinine ratio and CAN score, demonstrated that TcPO₂ levels were significantly and independently associated with current smoking (p = 0.013), ABI (p = 0.003), and NDS (p = 0.013).

CONCLUSION

Presence of DPN is independently associated with impaired cutaneous perfusion. Low TcPO₂ in subjects with DPN may contribute to delay in healing of diabetic foot ulcers, irrespectively of PAD.

A new look at painful diabetic neuropathy

The prevalence of diabetes mellitus and its chronic complications continue to increase alarmingly. Consequently, the massive expenditure on diabetic distal symmetrical polyneuropathy (DSPN) and its sequelae, will also likely rise. Up to 50% of patients with diabetes develop DSPN, and about 20% develop neuropathic pain (painful-DSPN). Painful-DSPN can cast a huge burden on sufferers' lives with increased rates of unemployment, mental health disorders and physical co-morbidities. Unfortunately, due to limited understanding of the mechanisms leading to painful-DSPN, current treatments remain inadequate. Recent studies examining the pathophysiology of painful-DSPN have identified maladaptive alterations at the level of both the peripheral and central nervous systems. Additionally, genetic studies have suggested that patients with variants of voltage gated sodium channels may be more at risk of developing neuropathic pain in the presence of a disease trigger such as diabetes. We review the recent advances in genetics, skin biopsy immunohistochemistry and neuro-imaging, which have the potential to further our understanding of the condition, and identify targets for new mechanism based therapies.

Diabetic Microvascular Disease: An Endocrine Society Scientific Statement

Both type 1 and type 2 diabetes adversely affect the microvasculature in multiple organs. Our understanding of the genesis of this injury and of potential interventions to prevent, limit, or reverse injury/dysfunction is continuously evolving. This statement reviews biochemical/cellular pathways involved in facilitating and abrogating microvascular injury. The statement summarizes the types of injury/dysfunction that occur in the three classical diabetes microvascular target tissues, the eye, the kidney, and the peripheral nervous system; the statement also reviews information on the effects of diabetes and insulin resistance on the microvasculature of skin, brain, adipose tissue, and cardiac and skeletal muscle. Despite extensive and intensive research, it is disappointing that microvascular complications of diabetes continue to compromise the quantity and quality of life for patients with diabetes. Hopefully, by understanding and building on current research findings, we will discover new approaches for prevention and treatment that will be effective for future generations.

Absent monofilament sensation in a type 2 diabetic feet

Neuropathy is a common complication which can affect up to 90% of patients with diabetes mellitus. Asymptomatic neuropathy is a common presentation. We present a case that emphasises the importance of foot screening in people with diabetes. It also highlights that patient education is key to prevent development of foot ulceration which can lead to amputations. In addition, pharmacological therapy (as per NICE guidance) can be offered for pain relief. Patients with diabetic neuropathy are at high risk of falling and sustaining fractures.

Treatment-Induced Neuropathy of Diabetes

PURPOSE OF REVIEW

Treatment-induced neuropathy of diabetes (TIND) is an under-recognized iatrogenic painful sensory and autonomic neuropathy. This review highlights the clinical symptoms and signs, raises awareness of the cause, and provides education about prevention of TIND.

RECENT FINDINGS

TIND may be triggered by a rapid decline in the blood glucose levels following the use of insulin, oral hypoglycemic medications, or even diet only to control diabetes. This may be seen in up to 10% of patients with diabetic neuropathy and has the potential for significant long-term complications that could be avoided through careful disease management. Based on the available evidence, a decrease in the glycosylated hemoglobin A1C of more than 3 points in 3 months in individuals with chronic hyperglycemia increases the risk of developing TIND. TIND is more common than previously suspected, and is tied to rates of glycemic control. Slower changes to glucose control are suggested, although there is no prospective data on disease prevention. Future research is necessary to guide treatment recommendations.

Murine model and mechanisms of treatment-induced painful diabetic neuropathy

Diabetes mellitus represents a group of metabolic diseases that are characterized by hyperglycemia caused by either lack of insulin production or a reduced ability to respond to insulin. It is estimated that there were 347 million people worldwide who suffered from diabetes in 2008 and incidence is predicted to double by 2050. Neuropathy is the most common complication of long-term diabetes and approximately 30% of these subjects develop chronic neuropathic pain. A distinct acute, severe form of neuropathic pain, called insulin neuritis or treatment-induced painful neuropathy of diabetes (TIND), may also occur shortly after initiation of intensive glycemic control, with an incidence rate of up to 10.9%. The pathological mechanisms leading to TIND, which is mostly unresponsive to analgesics, are not yet understood, impeding the development of therapies. Studies to date have been clinical and with limited cohorts of patients. In the current study, we developed chronic and acute insulin-induced neuropathic pain in mice with type 2 insulin-resistant diabetes. Furthermore, we determined that insulin-induced acute allodynia is independent of glycemia levels, can also be induced with Insulin-like Growth Factor 1 (IGF1) and be prevented by inhibition of AKT, providing evidence of an insulin/IGF1 signaling pathway-based mechanism for TIND. This mouse model is useful for the elucidation of mechanisms contributing to TIND and for the testing of new therapeutic approaches to treat TIND.

Treatment induced neuropathy of diabetes-Long term implications in type 1 diabetes

AIMS/HYPOTHESIS

Aggressive glucose control can result in treatment induced neuropathy of diabetes (TIND) if glycemic control is achieved too quickly. The aim of the present study is to describe the 8-year follow-up data on a cohort of individuals with type 1 diabetes who developed TIND.

METHODS

Twenty-six individuals with type 1 diabetes and TIND were followed longitudinally for 8years with regular quantitative measurement of pain, neurological examinations and evaluation of microvascular complications. Comprehensive neurological testing was performed after TIND and 7-8years later.

RESULTS

Among the 26 individuals with TIND, 19/26 had stable glycemic control and 7/26 had unstable glycemic control in long-term follow up. Those 19/26 with stable glycemic control had improvement in neuropathy, pain and microvascular complications while the 7/26 with unstable glycemic control had significant worsening of neuropathy, pain and microvascular complications (P<0.01, all tests).

CONCLUSION/INTERPRETATION

TIND is a poorly understood iatrogenic complication of aggressive glycemic control, although individuals with stable glycemic control tended to improve, while those with unstable glycemic control worsened. Additional studies of TIND are required to understand potential outcomes in an era of medical 'metrics' where physician reimbursement may be tied to achievement of excessively rapid glycemic control.

Enigma of painful diabetic neuropathy: can we use the basic science, research outcomes and real-world data to help improve patient care and outcomes?

The pathogenesis of painful diabetic neuropathy (PDN) is very complex and its detailed understanding often beyond the remit of the diabetologist or the diabetes multidisciplinary team. Nonetheless it is a very common and difficult to treat complication of diabetes, with significant co-morbidity and mortality, and some basic understanding may help the health care professional with its day to day management. In this review, we discuss the basic pathological mechanisms of PDN, and its clinical manifestations, and present both scientific and real world data on its management, in an attempt to help improve patient care and outcomes.

Diabetic peripheral neuropathy may not be as its name suggests: evidence from magnetic resonance imaging

Diabetic peripheral neuropathy (DPN) affects up to 50% of patients with diabetes and is a major cause of morbidity and increased mortality. Its clinical manifestations include distressing painful neuropathic symptoms and insensitivity to trauma that result in foot ulcerations and amputations. Several recent studies have implicated poor glycemic control, duration of diabetes, hyperlipidemia (particularly hypertryglyceridaemia), elevated albumin excretion rates, and obesity as risk factors for the development of DPN. However, similar data are not available for painful DPN. Moreover, although there is now strong evidence for the importance of peripheral nerve microvascular disease in the pathogenesis of DPN, peripheral structural biomarkers of painful DPN are lacking. However, there is now emerging evidence for the involvement of the central nervous system in both painful and painless DPN afforded by magnetic resonance imaging. This review will focus on this emerging evidence for central changes in DPN, hitherto considered a peripheral nerve disease only.

Painful diabetic neuropathy — current understanding and management for the primary care team

Primary care has an increasing role in the diagnosis and treatment of painful diabetic neuropathy (PDN), and early accurate diagnosis and intervention can greatly improve the prognosis. With the incidence of diabetes predicted to increase dramatically, the number of patients with PDN is set to soar. PDN can have a serious impact on quality of life, leading to severe depression and even suicide. The evolution of a schematic approach to the diagnosis and treatment of PDN can offer new hope to many patients. This review focuses on PDN and current treatment strategies. Many leading pain clinics have adopted a multidisciplinary approach to the pharmacological and non-pharmacological management of PDN.

Diabetic neuropathy: achieving best practice

Peripheral neuropathy is one of the commonest complications of diabetes and the commonest form of neuropathy in the developed world.1 Diabetic polyneuropathy encompasses several neuropathic syndromes, and the commonest presentation is chronic distal symmetrical neuropathy (DSP). DSP, often associated with autonomic neuropathy, has two clinical consequences: namely neuropathic pain and foot ulceration. Both often occur in the same individual, and cause severe curtailment of quality of life. The other, less common presentations of diabetic polyneuropathy include acute painful neuropathies, and focal neuropathies (amyotrophy, pressure palsies, truncal radiculopathies, mononeuropathies and mononeuritis multiplex).2 Table 1 shows a recent classification of diabetic polyneuropathy based upon the natural history of the various syndromes.3

Diabetic autonomic neuropathy

Diabetes mellitus is the commonest cause of an autonomic neuropathy in the developed world. Diabetic autonomic neuropathy causes a constellation of symptoms and signs affecting cardiovascular, urogenital, gastrointestinal, pupillomotor, thermoregulatory, and sudomotor systems. Several discrete syndromes associated with diabetes cause autonomic dysfunction. The most prevalent of these are: generalized diabetic autonomic neuropathy, autonomic neuropathy associated with the prediabetic state, treatment-induced painful and autonomic neuropathy, and transient hypoglycemia-associated autonomic neuropathy. These autonomic manifestations of diabetes are responsible for the most troublesome and disabling features of diabetic peripheral neuropathy and result in a significant proportion of the mortality and morbidity associated with the disease.

Updates in diabetic peripheral neuropathy

Diabetes has become one of the largest global health-care problems of the 21 ^st century. According to the Centers for Disease Control and Prevention, the population prevalence of diabetes in the US is approaching 10% and is increasing by 5% each year. Diabetic neuropathy is the most common complication associated with diabetes mellitus. Diabetes causes a broad spectrum of neuropathic complications, including acute and chronic forms affecting each level of the peripheral nerve, from the root to the distal axon. This review will focus on the most common form, distal symmetric diabetic polyneuropathy. There has been an evolution in our understanding of the pathophysiology and the management of diabetic polyneuropathy over the past decade. We highlight these new perspectives and provide updates from the past decade of research.

'Insulin neuritis' to 'treatment-induced neuropathy of diabetes': new name, same mystery

Insulin neuritis is a historical term for an acute neuropathy affecting patients with diabetes who achieve rapid re-establishment of previously poor glycaemic control. It presents with neuropathic pain, symptoms of autonomic dysfunction or a combination of both. Recently, it has been proposed that 'treatment-induced neuropathy of diabetes' would be a more accurate name for this entity. The management focuses on controlling the symptoms while they gradually improve with time.

Understanding and treating painful diabetic neuropathy: time for a paradigm shift

The pathogenesis of diabetic neuropathy (DN) continues to be unclear and as a result, progress in developing effective therapies has been disappointing. In particular, there is only limited understanding of why some patients suffer severe chronic pain, whilst others have painless symptoms. Assessment of the peripheral nerves frequently shows no differences between painful and painless DN. There is growing evidence that the nerve damage in DN is more generalized, including the central nervous system, and these central changes are key to the development and persistence of pain in DN. The advent of new radiological techniques provides us with non-invasive modalities to study central pathophysiological processes in greater detail. These insights are increasingly leading to the recognition that painful DN is a complex and heterogeneous disorder, which requires a multimodal approach to treatment.

Small-Fiber Neuropathy: A Diabetic Microvascular Complication of Special Clinical, Diagnostic, and Prognostic Importance

Damage of small nerve fibers may lead to a large variety of clinical symptoms. Small-fiber neuropathy underlies the symptoms of painful diabetic neuropathy, which may decrease quality of life. It also contributes to the poor prognosis of diabetic neuropathy because it plays a key role in the pathogenesis of foot ulceration and autonomic neuropathy. Impairment of small nerve fibers is considered the earliest alteration in the course of diabetic neuropathy. Therefore, assessment of functional and morphological abnormalities of small nerve fibers may enable timely diagnosis. The definition, symptoms, and clinical significance of small-fiber neuropathy are considered in the present review. An apparently more complex interaction between small-fiber impairment and microcirculation is extensively discussed. Diagnostic modalities include morphometric and functional methods. Corneal confocal microscopy and punch skin biopsy are considered gold standards, but noninvasive functional tests are also diagnostically useful. However, in routine clinical practice, small-fiber neuropathy is diagnosed by its typical clinical presentation. Finally, prompt treatment should be initiated following diagnosis.

The effects of capillary dysfunction on oxygen and glucose extraction in diabetic neuropathy

Diabetic neuropathy is associated with disturbances in endoneurial metabolism and microvascular morphology, but the roles of these factors in the aetiopathogenesis of diabetic neuropathy remain unclear. Changes in endoneurial capillary morphology and vascular reactivity apparently predate the development of diabetic neuropathy in humans, and in manifest neuropathy, reductions in nerve conduction velocity correlate with the level of endoneurial hypoxia. The idea that microvascular changes cause diabetic neuropathy is contradicted, however, by reports of elevated endoneurial blood flow in early experimental diabetes, and of unaffected blood flow when early histological signs of neuropathy first develop in humans. We recently showed that disturbances in capillary flow patterns, so-called capillary dysfunction, can reduce the amount of oxygen and glucose that can be extracted by the tissue for a given blood flow. In fact, tissue blood flow must be adjusted to ensure sufficient oxygen extraction as capillary dysfunction becomes more severe, thereby changing the normal relationship between tissue oxygenation and blood flow. This review examines the evidence of capillary dysfunction in diabetic neuropathy, and whether the observed relation between endoneurial blood flow and nerve function is consistent with increasingly disturbed capillary flow patterns. The analysis suggests testable relations between capillary dysfunction, tissue hypoxia, aldose reductase activity, oxidative stress, tissue inflammation and glucose clearance from blood. We discuss the implications of these predictions in relation to the prevention and management of diabetic complications in type 1 and type 2 diabetes, and suggest ways of testing these hypotheses in experimental and clinical settings.

[Diabetic neuropathy: do not only consider distal symmetrical neuropathy]

BACKGROUND

Diabetic neuropathy is a common complication of diabetes mellitus. The length-dependent symmetrical sensorimotor type of neuropathy is the most prevalent form of diabetic neuropathy but other forms of diabetic neuropathy also need to be kept in mind. Their differential diagnosis is often more challenging but implicates specific forms of treatment other than improvement of metabolic control.

AIM OF THE STUDY

This article gives an overview of the less frequent forms of diabetic neuropathy and discusses their impact, diagnostic and therapeutic implications.

RESULTS

Autonomic diabetic neuropathy, diabetic small fiber neuropathy and less frequent forms of diabetic neuropathy, such as diabetic radiculoplexopathy, diabetic neuropathy of cranial nerves, therapy-induced neuropathy and alternative causes of peripheral neuropathy in patients with diabetes are described.

DISCUSSION

Diagnosis of less frequent subtypes of diabetic neuropathy and differentiation towards alternative causes of peripheral neuropathy are often difficult in daily medical routine. Diagnostic clues are helpful in identifying rarer forms of diabetic neuropathy, thus enabling more specific treatment.

Treatment-induced neuropathy of diabetes: an acute, iatrogenic complication of diabetes

Treatment-induced neuropathy in diabetes (also referred to as insulin neuritis) is considered a rare iatrogenic small fibre neuropathy caused by an abrupt improvement in glycaemic control in the setting of chronic hyperglycaemia. The prevalence and risk factors of this disorder are not known. In a retrospective review of all individuals referred to a tertiary care diabetic neuropathy clinic over 5 years, we define the proportion of individuals that present with and the risk factors for development of treatment-induced neuropathy in diabetes. Nine hundred and fifty-four individuals were evaluated for a possible diabetic neuropathy. Treatment-induced neuropathy in diabetes was defined as the acute onset of neuropathic pain and/or autonomic dysfunction within 8 weeks of a large improvement in glycaemic control-specified as a decrease in glycosylated haemoglobin A1C (HbA1c) of ≥2% points over 3 months. Detailed structured neurologic examinations, glucose control logs, pain scores, autonomic symptoms and other microvascular complications were measured every 3-6 months for the duration of follow-up. Of 954 patients evaluated for diabetic neuropathy, 104/954 subjects (10.9%) met criteria for treatment-induced neuropathy in diabetes with an acute increase in neuropathic or autonomic symptoms or signs coinciding with a substantial decrease in HbA1c. Individuals with a decrease in HbA1c had a much greater risk of developing a painful or autonomic neuropathy than those individuals with no change in HbA1c (P < 0.001), but also had a higher risk of developing retinopathy (P < 0.001) and microalbuminuria (P < 0.001). There was a strong correlation between the magnitude of decrease in HbA1c, the severity of neuropathic pain (R = 0.84, P < 0.001), the degree of parasympathetic dysfunction (R = -0.52, P < 0.01) and impairment of sympathetic adrenergic function as measured by fall in blood pressure on tilt-table testing (R = -0.63, P < 0.001). With a decrease in HbA1c of 2-3% points over 3 months there was a 20% absolute risk of developing treatment-induced neuropathy in diabetes, with a decrease in HbA1c of >4% points over 3 months the absolute risk of developing treatment-induced neuropathy in diabetes exceeded 80%. Treatment-induced neuropathy of diabetes is an underestimated iatrogenic disorder associated with diffuse microvascular complications. Rapid glycaemic change in patients with uncontrolled diabetes increases the risk of this complication.

Surgical decompression of painful diabetic peripheral neuropathy: the role of pain distribution

Objective

To investigate the effect of surgical decompression on painful diabetic peripheral neuropathy (DPN) patients and discuss the role which pain distribution and characterization play in the management of painful DPN as well as the underlying mechanism involved.

Methods

A total of 306 patients with painful diabetic lower-extremity neuropathy were treated with Dellon surgical nerve decompression in our department. Clinical evaluation including Visual analogue scale (VAS), Brief Pain Inventory Short Form for diabetic peripheral neuropathy (BPI-DPN) questionnaire, two-point discrimination (2-PD), nerve conduction velocity (NCV) and high-resolution ultrasonography (cross-sectional area, CSA) were performed in all cases preoperatively, and at 6 month intervals for 2 years post-decompression. The patients who underwent surgery were retrospectively assigned into two subgroups (focal and diffuse pain) according to the distribution of the diabetic neuropathic pain. The control group included 92 painful DPN patients without surgery.

Results

The levels of VAS, scores in BPI-DPN, 2-PD, NCV results and CSA were all improved in surgical group when compared to the control group (P<0.05). More improvement of VAS, scores in BPI-DPN and CSA was observed in focal pain group than that in diffuse group (P<0.05).

Conclusions

Efficacy of decompression of multiple lower-extremity peripheral nerves in patients with painful diabetic neuropathy was confirmed in this study. While both focal and diffuse group could benefit from surgical decompression, pain relief and morphological restoration could be better achieved in focal group.

Diabetic neuropathy: mechanisms, emerging treatments, and subtypes

Diabetic neuropathies (DNs) differ in clinical course, distribution, fiber involvement (type and size), and pathophysiology, the most typical type being a length-dependent distal symmetric polyneuropathy (DSP) with differing degrees of autonomic involvement. The pathogenesis of diabetic DSP is multifactorial, including increased mitochondrial production of free radicals due to hyperglycemia-induced oxidative stress. Mechanisms that impact neuronal activity, mitochondrial function, membrane permeability, and endothelial function include formation of advanced glycosylation end products, activation of polyol aldose reductase signaling, activation of poly(ADP ribose) polymerase, and altered function of the Na(+)/K(+)-ATPase pump. Hyperglycemia-induced endoplasmic reticulum stress triggers several neuronal apoptotic processes. Additional mechanisms include impaired nerve perfusion, dyslipidemia, altered redox status, low-grade inflammation, and perturbation of calcium balance. Successful therapies require an integrated approach targeting these mechanisms. Intensive glycemic control is essential but is insufficient to prevent onset or progression of DSP, and disease-modifying treatments for DSP have been disappointing. Atypical forms of DN include subacute-onset sensory (symmetric) or motor (asymmetric) predominant conditions that are frequently painful but generally self-limited. DNs are a major cause of disability, associated with reduced quality of life and increased mortality.

The relationship between blood pressure and sciatic nerve blood flow velocity in rats with insulin-treated experimental diabetes

Peripheral nerve blood flow (NBF) does not autoregulate but, instead, responds passively to changes in mean arterial pressure (MAP). How this relationship is impacted by insulin-treated experimental diabetes (ITED) is unknown. We tested the hypothesis that ITED will reduce NBF across a range of MAP in Sprague Dawley rats. Following 10 weeks of control or ITED conditions, conscious MAP (tail-cuff) was measured, and under anaesthesia, the MAP (carotid artery catheter, pressure transducer) and NBF (Doppler ultrasound, 40 MHz) responses to sodium nitroprusside (60 µg/kg) and phenylephrine (12 µg/kg) infusion were recorded (regression equations for MAP vs NBF were created for each rodent). Thereafter, motor nerve conduction velocity (MNCV) and nerve vascularization (haematoxylin and eosin stain) were determined. Conscious MAP was higher and MNCV was lower in the ITED group (p < 0.01). In response to drug infusions, the ΔMAP and ΔNBF were similar between groups (p ≥ 0.18). Estimated conscious NBF (based on substituting conscious MAP values into each individual regression equation) was greater in the ITED group (p < 0.01). Sciatic nerve vascularization was similar between groups (p ≥ 0.50). In contrast to the hypothesis, NBF was not reduced across a range of MAP. In spite of increased estimated conscious NBF values, MNCV was reduced in rats with ITED.

Exercise training enhances insulin-stimulated nerve arterial vasodilation in rats with insulin-treated experimental diabetes

Insulin stimulates nerve arterial vasodilation through a nitric oxide (NO) synthase (NOS) mechanism. Experimental diabetes reduces vasa nervorum NO reactivity. Studies investigating hyperglycemia and nerve arterial vasodilation typically omit insulin treatment and use sedentary rats resulting in severe hyperglycemia. We tested the hypotheses that 1) insulin-treated experimental diabetes and inactivity (DS rats) will attenuate insulin-mediated nerve arterial vasodilation, and 2) deficits in vasodilation in DS rats will be overcome by concurrent exercise training (DX rats; 75–85% V̇o2 max, 1 h/day, 5 days/wk, for 10 wk). The baseline index of vascular conductance values (VCi = nerve blood flow velocity/mean arterial blood pressure) were similar ( P ≥ 0.68), but peak VCi and the area under the curve (AUCi) for the VCi during a euglycemic hyperinsulinemic clamp (EHC; 10 mU·kg−1·min−1) were lower in DS rats versus control sedentary (CS) rats and DX rats ( P ≤ 0.01). Motor nerve conduction velocity (MNCV) was lower in DS rats versus CS rats and DX rats ( P ≤ 0.01). When compared with DS rats, DX rats expressed greater nerve endothelial NOS (eNOS) protein content ( P = 0.04). In a separate analysis, we examined the impact of diabetes in exercise-trained rats alone. When compared with exercise-trained control rats (CX), DX rats had a lower AUCi during the EHC, lower MNCV values, and lower sciatic nerve eNOS protein content ( P ≤ 0.03). Therefore, vasa nervorum and motor nerve function are impaired in DS rats. Such deficits in rats with diabetes can be overcome by concurrent exercise training. However, in exercise-trained rats (CX and DX groups), moderate hyperglycemia lowers vasa nervorum and nerve function.

Pathogenesis of painful diabetic neuropathy

The prevalence of diabetes is rising globally and, as a result, its associated complications are also rising. Painful diabetic neuropathy (PDN) is a well-known complication of diabetes and the most common cause of all neuropathic pain. About one-third of all diabetes patients suffer from PDN. It has a huge effect on a person's daily life, both physically and mentally. Despite huge advances in diabetes and neurology, the exact mechanism of pain causation in PDN is still not clear. The origin of pain could be in the peripheral nerves of the central nervous system. In this review, we discuss various possible mechanisms of the pathogenesis of pain in PDN. We discuss the role of hyperglycaemia in altering the physiology of peripheral nerves. We also describe central mechanisms of pain.

Painful diabetic neuropathy: clinical aspects

Painful diabetic neuropathy (PDN) is one of several clinical syndromes in patients with diabetic peripheral neuropathy (DPN) and presents a major challenge for optimal management. The epidemiology of PDN has not been extensively studied. On the basis of available data, the prevalence of pain ranges from 10% to 20% in patients with diabetes and from 40% to 50% in those with diabetic neuropathy. Neuropathic pain can be disabling and devastating, with a significant impact on the patient's quality of life and associated healthcare cost. Pathophysiologic mechanisms underlying PDN are similar to other neuropathic pain disorders and broadly invoke peripheral and central sensitization. The natural course of PDN is variable, with the majority of patients experiencing spontaneous improvement and resolution of pain. Quantifying neuropathic pain is difficult, especially in clinical practice, but has improved recently in clinical trials with the development of neuropathic pain-specific tools, such as the Neuropathic Pain Questionnaire and the Neuropathic Pain Symptom Inventory. Hyperglycemia-induced pathways result in nerve dysfunction and damage, which lead to hyperexcitable peripheral and central pathways of pain. Glycemic control may prevent or partially reverse DPN and modulate PDN.

Pharmacologic management of diabetic peripheral neuropathic pain

INTRODUCTION

Diabetic peripheral neuropathic pain (DPNP) is a debilitating and distressing complication that occurs in patients with diabetes mellitus. This article provides an overview of diabetic peripheral neuropathy focusing on DPNP.

AREAS COVERED

This article reviews the diagnosis, pathogenesis, prevention and treatment of diabetic neuropathy and neuropathic pain. A comprehensive and systematic Medline search of the published literature for treatment of diabetic peripheral neuropathy was done from 1965 to December 2012. Studies not in English language were excluded.

EXPERT OPINION

Neuropathic pain is difficult to treat, and patients rarely experience complete pain relief. Despite several pharmacological agents being used in the treatment of DPNP, only duloxetine and pregabalin have evidence-based support for controlling DPNP.