The natural history of painful diabetic neuropathy--a 4-year study

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.

Decompression nerve surgery for diabetic neuropathy: a structured review of published clinical trials

AIM

To assess lower extremity decompression nerve surgery (DNS) to treat the consequences of diabetic distal symmetric peripheral neuropathy (DPN).

RESEARCH DESIGN AND METHODS

MEDLINE, PubMed, and related registries were searched through December 2017 to identify randomized, quasi-randomized or observational trials that evaluated the efficacy of lower extremity DNS on pain relief (primary outcome) or other secondary outcomes. Observational studies were included, given investigators' reluctance to use sham surgery controls. Outcome effect size was estimated, and a weighted average was calculated.

RESULTS

Eight of 23 studies evaluated pain relief, including a double-blind randomized controlled trial (with a sham surgery leg), an unblinded trial with a nonsurgical control leg, and 6 observational studies. All reported substantial pain relief post-DNS with average effect sizes between two and five. Unexpectedly, the double-blind trial showed improvement in the sham leg comparable to the DNS leg and exceeding the improvement observed in the nonsurgical leg in the unblinded study. Sensory testing showed generally favorable results supporting DNS, and nerve conduction velocities increased post-DNS relative to deterioration in controls. Ultrasound revealed fusiform nerve swelling near compression sites. Morphological results of DNS were generally favorable but inconsistent, whereas hemodynamic measures showed a positive effect on arterial parameters, as did transcutaneous oximetry (improved microcirculation). The incidence of initial and recurrent neuropathic diabetic foot ulcers appeared reduced post-DNS relative to the contralateral foot (borderline significant).

CONCLUSION

The data remain insufficient to recommend DNS for painful DPN, given conflicting and unexpectedly positive results involving sham surgery relative to unblinded controls. The generally supportive sensory and nerve conduction results are compromised by methodological issues, whereas more favorable results support DNS to prevent new or recurrent neuropathic foot ulcers. Future studies need to clarify subject selection vis-à-vis DPN vs superimposed compressed nerves, utilize appropriate validated instruments, and readdress use of sham surgical controls in light of recent results.

Efficient conditioned pain modulation despite pain persistence in painful diabetic neuropathy

Despite persistent clinical pain in patients with painful diabetic neuropathy, longer pain duration was associated with more efficient CPM.

Introduction:

Alleviation of pain, by either medical or surgical therapy, is accompanied by transition from less efficient, or pro-nociceptive, to efficient conditioned pain modulation (CPM). Spontaneous decrease or resolution of pain with disease progression is reported for some patients with painful diabetic neuropathy (PDN).

Objectives:

To explore whether CPM changes similarly in parallel to spontaneous resolution of pain in PDN patients.

Methods:

In this cross-sectional study, thirty-three patients with PDN underwent psychophysical assessment of pain modulation on the forearm, remote from the clinical pain.

Results:

Pain duration was not correlated with neuropathic pain intensity, yet, it correlated with CPM efficiency; patients with longer pain duration had same pain level, but more efficient CPM than those with short-pain duration (ρ = −0.417; P = 0.025, Spearman correlation). Patients with pain more than 2 years (median split) expressed efficient CPM that was not different from that of healthy controls. These patients also had lower temporal summation of pain than the short-pain duration patients group (P < 0.05). The 2 patient groups did not differ in clinical pain characteristics or use of analgesics.

Conclusion:

Pro-nociception, expressed by less efficient CPM and high temporal summation that usually accompanies clinical painful conditions, seems to “normalize” with chronicity of the pain syndrome. This is despite continuing pain, suggesting that pro-nociceptivity in pain syndromes is multifactorial. Because the pain modulation profile affects success of therapy, this suggests that different drugs might express different efficacy pending on duration of the pain in patients with PDN.

Practical Management of Patients With Painful Diabetic Neuropathy

Purpose

Painful diabetic neuropathy (PDN) has a significant impact on patients’ quality of life, affecting sleep, mood, mobility, ability to work, interpersonal relationships, overall self-worth, and independence. The purpose of this article is to provide diabetes educators with current and essential tools for PDN assessment and management.

Methods

Medline and CINAHL database searches identified publications on the assessment and treatment of PDN. Identified research was evaluated, and information pertinent to diabetes educators was summarized.

Results

Recent advancements in assessment of neuropathic pain include identifying characteristics that distinguish between neuropathic and nonneuropathic pain. In the absence of treatment, research demonstrates that nerve damage may progress while pain diminishes. Many disease-modifying and symptom-management treatment options are available.

Conclusion

Good glycemic control is the first priority for both prevention and management of PDN. However, even with good glycemic control, up to 20% of patients will develop PDN. PDN recognition and assessment are critical to optimize management. Although several treatment modalities are available, few patients obtain complete pain relief. Recent advances in understanding the mechanisms underlying neuropathic pain should lead to better treatment and patient outcomes. Combination therapy, including nonpharmacologic modalities, may be required. Research evaluating the efficacy of combination therapy is needed.

Pain modulation from the brain during diabetic neuropathy: Uncovering the role of the rostroventromedial medulla

Diabetic neuropathy has a profound impact in the quality of life of patients who frequently complain of pain. The mechanisms underlying diabetic neuropathic pain (DNP) are no longer ascribed only to damage of peripheral nerves. The effects of diabetes at the central nervous system are currently considered causes of DPN. Management of DNP may be achieved by antidepressants that act on serotonin (5-HT) uptake, namely specific serotonin reuptake inhibitors. The rostroventromedial medulla (RVM) is a key pain control center involved in descending pain modulation at the spinal cord through local release of 5-HT and plays a peculiar role in the balance of bidirectional control (i.e. inhibitory and facilitatory) from the brain to the spinal cord. This review discusses recently uncovered neurobiological mechanisms that mediate nociceptive modulation from the RVM during diabetes installation. In early phases of the disease, facilitation of pain modulation from the RVM prevails through a triplet of mechanisms which include increase in serotonin expression at the RVM and consequent rise of serotonin levels at the spinal cord and upregulation of local facilitatory 5HT3 receptors, enhancement of spontaneous activity of facilitatory RVM neurons and up-regulation of the expression of transient receptor potential vanilloid type 1 (TRPV1) receptor. With the progression of diabetes the alterations in the RVM increase dramatically, with oxidative stress and neuronal death associated to microglia-mediated inflammation. In a manner similar to other central areas, like the thalamus, the RVM is likely to be a "pain generator/amplifier" during diabetes, accounting to increase DNP. Early interventions in DNP prevention using strategies that simultaneously tackle the exacerbation of 5-HT3 spinal receptors and of microglial RVM activity, namely those that increase the levels of anti-inflammatory cytokines, should be considered in the future of DNP treatment.

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

Painful Neuropathy with Trigeminal Nerve Involvement in Type 2 Diabetes

After several years of treatment for type 2 diabetes mellitus, a 69-year-old Japanese man developed an acute painful neuropathy, characterized by bilateral causalgia and dysaesthesia in his cheeks and around his eyes, typically 30 min to 3h after meals. As his glycaemic control deteriorated, his haemoglobin (Hb) A1c level gradually increased from 7-8% to 10.3% and his symptoms became more severe. The pain radiated out along the distribution of the ophthalmic and maxillary divisions of the trigeminal nerve. The patient was treated with insulin therapy and his HbA1c level decreased from 10.3% to 6.8% within 7 months. Five months after initiating insulin therapy, his symptoms showed a dramatic improvement. This was a very unusual case of bilateral acute painful neuropathy that involved the ophthalmic and maxillary divisions of the trigeminal nerve, and in which aggravation of the symptoms clearly related to poor glycaemic control.

An Epidemiological Study of Neuropathic Pain Symptoms in Canadian Adults

The reported prevalence of neuropathic pain ranges from 6.9% to 10%; however the only Canadian study reported 17.9%. The objective of this study was to describe the epidemiology of neuropathic pain in Canada. A cross-sectional survey was conducted in a random sample of Canadian adults. The response rate was 21.1% (1504/7134). Likely or possible neuropathic pain was defined using a neuropathic pain-related diagnosis and a positive outcome on the Self-Report Leeds Assessment of Neuropathic Symptoms and Signs pain scale (S-LANSS) or the Douleur Neuropathique 4 (DN4) Questions. The prevalence of likely neuropathic pain was 1.9% (S-LANSS) and 3.4% (DN4) and that of possible neuropathic pain was 5.8% (S-LANSS) and 8.1% (DN4). Neuropathic pain was highest in economically disadvantaged males. There is a significant burden of neuropathic pain in Canada. The low response rate and a slightly older and less educated sample than the Canadian population may have led to an overestimate of neuropathic pain. Population prevalence varies by screening tool used, indicating more work is needed to develop reliable measures. Population level screening targeted towards high risk groups should improve the sensitivity and specificity of screening, while clinical examination of those with positive screening results will further refine the estimate of prevalence.

Recent advances in the management of diabetic distal symmetrical polyneuropathy

There is now little doubt that poor blood glucose control is an important risk factor for the development of diabetic peripheral neuropathy (DPN). Furthermore, traditional cardiovascular risk factors for macrovascular disease appear to be associated with an increased risk of DPN. The recently established International Expert Group on Diabetic Neuropathy has recommended new criteria for the diagnosis of DPN in the context of clinical and research settings. Studies in experimental diabetes examining the pathogenesis of DPN have identified a number of metabolic abnormalities including polyol pathway hyperactivity, increased advanced glycation end‐point formation, alterations in the protein kinase C beta pathway through diacylglycerol and oxidative stress. There is now strong evidence implicating nerve ischemia as the cause of DPN. Studies in human and animal models have shown reduced nerve perfusion and endoneurial hypoxia. These endoneurial microvascular changes strongly correlate with clinical severity and the degree of nerve‐fiber pathology. Unfortunately, many compounds that have been effective in animal models of neuropathy have not been successful in human diabetic neuropathy. The only compounds found to be efficacious in human diabetic neuropathy, and are in clinical use, are the anti‐oxidant, α‐lipoic acid and the aldose reductase inhibitor, epalrestat. Overall, the evidence emphasizes the importance of vascular dysfunction, driven by metabolic change, in the etiology of DPN, and highlights potential therapeutic approaches. Epidemiological data on diabetic painful neuropathic pain (DPNP) are limited. In one population‐based study, the prevalence of DPNP, as assessed by a structured questionnaire and examination, was estimated at 16%. It was notable that, of these patients, 12.5% had never reported symptoms to their doctor and 39% had never received treatment for their pain. Thus, despite being common, DPNP continues to be underdiagnosed and undertreated. Pharmacological treatment of DPNP include tricyclic compounds, serotonin noradrenalin reuptake inhibitors, the anti‐oxidant α‐lipoic acid, anticonvulsants, opiates, membrane stabilizers, topical capsaicin and so on. Management of the patient with DPNP must be tailored to individual requirements and will depend on the presence of other comorbidities. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00083.x)

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.

Cross sectional study to evaluate the effect of duration of type 2 diabetes mellitus on the nerve conduction velocity in diabetic peripheral neuropathy

OBJECTIVE

To study the nerve conduction velocity in clinically undetectable and detectable peripheral neuropathy in type 2 diabetes mellitus with variable duration.

MATERIAL AND METHODS

This cross sectional study was conducted in diagnosed type 2 diabetes mellitus patients. They were divided in groups: Group I (n=37) with clinically detectable diabetic peripheral neuropathy of shorter duration and Group II (n=27) with clinically detectable diabetic peripheral neuropathy of longer duration. They were compared with T2DM patients (n=22) without clinical neuropathy. Clinical diagnosis was based on neuropathy symptom score (NSS) and neuropathy disability score (NDS) for signs. Nerve conduction velocity was measured in both upper and lower limbs. Median, ulnar, common peroneal and posterior tibial nerves were selected for motor nerve conduction study and median and sural nerves were selected for sensory nerve conduction study.

RESULTS

The comparisons were done between nerve conduction velocities of motor and sensory nerves in patients of clinically detectable neuropathy and patients without neuropathy in type 2 diabetes mellitus population. This study showed significant electrophysiological changes with duration of disease. Nerve conduction velocities in lower limbs were significantly reduced even in patients of shorter duration with normal upper limb nerve conduction velocities.

CONCLUSION

Diabetic neuropathy symptom score (NSS) and neuropathy disability score (NDS) can help in evaluation of diabetic sensorimotor polyneuropathy though nerve conduction study is more powerful test and can help in diagnosing cases of neuropathy.

Mechanisms and management of diabetic painful distal symmetrical polyneuropathy

Although a number of the diabetic neuropathies may result in painful symptomatology, this review focuses on the most common: chronic sensorimotor distal symmetrical polyneuropathy (DSPN). It is estimated that 15-20% of diabetic patients may have painful DSPN, but not all of these will require therapy. In practice, the diagnosis of DSPN is a clinical one, whereas for longitudinal studies and clinical trials, quantitative sensory testing and electrophysiological assessment are usually necessary. A number of simple numeric rating scales are available to assess the frequency and severity of neuropathic pain. Although the exact pathophysiological processes that result in diabetic neuropathic pain remain enigmatic, both peripheral and central mechanisms have been implicated, and extend from altered channel function in peripheral nerve through enhanced spinal processing and changes in many higher centers. A number of pharmacological agents have proven efficacy in painful DSPN, but all are prone to side effects, and none impact the underlying pathophysiological abnormalities because they are only symptomatic therapy. The two first-line therapies approved by regulatory authorities for painful neuropathy are duloxetine and pregabalin. α-Lipoic acid, an antioxidant and pathogenic therapy, has evidence of efficacy but is not licensed in the U.S. and several European countries. All patients with DSPN are at increased risk of foot ulceration and require foot care, education, and if possible, regular podiatry assessment.

Painful and painless diabetic neuropathy: one disease or two?

Painful diabetic polyneuropathy (PDPN) is generally considered a variant of diabetic polyneuropathy (DPN) but the identification of distinctive aspects that characterize painful compared with painless DPN has however been addressed in many studies, mainly with the purpose of better understanding the mechanisms of neuropathic pain in the scenario of peripheral nerve damage of DPN, of determining risk markers for pain development, and also of recognizing who might respond to treatments. This review is aimed at examining available literature dealing with the issue of similarities and differences between painful and painless DPN in an attempt to respond to the question of whether painful and painless DPN are the same disease or not and to address the conundrum of why some people develop the insensate variety of DPN whilst others experience distressing pain. Thus, from the perspective of comparing painful with painless forms of DPN, this review considers the clinical correlates of PDPN, its distinctive framework of symptoms, signs, and nerve functional and structural abnormalities, the question of large and small fiber involvement, the peripheral pain mechanisms, the central processing of pain and some new insights into the pathogenesis of pain in peripheral polyneuropathies and PDPN.

Guidelines in the management of diabetic nerve pain: clinical utility of pregabalin

Diabetic peripheral neuropathy is a common complication of diabetes. It presents as a variety of syndromes for which there is no universally accepted unique classification. Sensorimotor polyneuropathy is the most common type, affecting about 30% of diabetic patients in hospital care and 25% of those in the community. Pain is the reason for 40% of patient visits in a primary care setting, and about 20% of these have had pain for greater than 6 months. Chronic pain may be nociceptive, which occurs as a result of disease or damage to tissue with no abnormality in the nervous system. In contrast, neuropathic pain is defined as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system." Persistent neuropathic pain interferes significantly with quality of life, impairing sleep and recreation; it also significantly impacts emotional well-being, and is associated with depression, anxiety, and noncompliance with treatment. Painful diabetic peripheral neuropathy is a difficult-to-manage clinical problem, and patients with this condition are more apt to seek medical attention than those with other types of diabetic neuropathy. Early recognition of psychological problems is critical to the management of pain, and physicians need to go beyond the management of pain per se if they are to achieve success. This evidence-based review of the assessment of the patient with pain in diabetes addresses the state-of-the-art management of pain, recognizing all the conditions that produce pain in diabetes and the evidence in support of a variety of treatments currently available. A search of the full Medline database for the last 10 years was conducted in August 2012 using the terms painful diabetic peripheral neuropathy, painful diabetic peripheral polyneuropathy, painful diabetic neuropathy and pain in diabetes. In addition, recent reviews addressing this issue were adopted as necessary. In particular, reports from the American Academy of Neurology and the Toronto Consensus Panel on Diabetic Neuropathy were included. Unfortunately, the results of evidence-based studies do not necessarily take into account the presence of comorbidities, the cost of treatment, or the role of third-party payers in decision-making. Thus, this review attempts to give a more balanced view of the management of pain in the diabetic patient with neuropathy and in particular the role of pregabalin.

A spinal mechanism of action for duloxetine in a rat model of painful diabetic neuropathy

BACKGROUND AND PURPOSE

This study was designed to clarify mechanisms responsible for the anti-allodynic effects of duloxetine in diabetes.

EXPERIMENTAL APPROACH

The streptozotocin-induced diabetic rat model was used to compare the efficacy of duloxetine, 5-HT, the 5-HT(2A) receptor agonist [1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI)] and two antagonists (ketanserin and pruvanserin) on tactile allodynia.

KEY RESULTS

Systemic or intrathecal injection of duloxetine alleviated tactile allodynia in diabetic rats. The effect of systemic duloxetine was reduced by intrathecal administration of ketanserin or pruvanserin, indicating participation of spinal 5-HT(2A) receptors in the mechanism of action of duloxetine. In contrast to spinal delivery, systemic and local peripheral injections of ketanserin or pruvanserin alleviated tactile allodynia in diabetic rats. This effect was reversed immediately after systemic or local DOI injection.

CONCLUSIONS AND IMPLICATIONS

These results support the involvement of spinal 5-HT(2A) receptors in the ability of duloxetine to ameliorate painful diabetic neuropathy. Our data also suggest that the role of 5-HT(2A) receptors depends on the level of the neuraxis at which activation takes place, with peripheral activation contributing to tactile allodynia in diabetic rats, whereas spinal activation of this receptor alleviates tactile allodynia. The development of selective peripheral 5-HT(2A) receptor antagonists may offer a novel approach for the treatment of diabetic neuropathic pain.

Diabetes induces changes in ILK, PINCH and components of related pathways in the spinal cord of rats

Recent work suggests that diabetes affects processing of peripheral, spinal and supraspinal signals in the spinal cord. However, there is little evidence for spinal cord lesions that would account for alterations in behavioral responses induced by experimental diabetes. Therefore, we assessed the expression of proteins that might affect neuronal cytoskeletal stability and thus promote dendritic and synaptic reorganization in diabetic rats. Expression of ILK, PINCH, PI3K, GSK-3beta, tau, MAP2, synaptophysin and drebrin in the lumbar spinal cord of non-diabetic and streptozotocin-diabetic rats was assessed by Western-blot analysis and immunocytochemistry after 8 and 20weeks of diabetes. The impact of diabetes on the proteins studied was duration-dependent with changes observed after 20 but not 8weeks of diabetes. ILK and PINCH proteins levels were significantly decreased and both colocalized to neurons and oligodendrocytes. PI3K protein levels were also significantly decreased, while GSK-3beta activity tended to be increased. Phosphorylation of tau and MAP2A/B protein expression were significantly increased, and expression of synaptophysin and drebrin were reduced in diabetic rats. Decreased ILK and PINCH as well as alterations of components of related signaling pathways are associated with tau hyperphosphorylation, MAP2 overexpression and reduction of synaptic proteins in the spinal cord of diabetic rats, suggesting that ILK and PINCH contribute to stabilization of axonal and dendritic structures. However, these changes are not likely the cause of altered behavioral responses in diabetic rats that occur after short-term diabetes, but may contribute to structural changes occurring in long-term diabetes.

Switching from pathogenetic treatment with alpha-lipoic acid to gabapentin and other analgesics in painful diabetic neuropathy: a real-world study in outpatients

In this retrospective real-world study, we aimed to evaluate whether switching from the pathogenetic treatment option alpha-lipoic acid to drugs for symptomatic treatment of neuropathic pain such as gabapentin would be associated with changes in efficacy, safety, and cost-effectiveness. A cohort of 443 diabetic patients with chronic painful neuropathy were treated with alpha-lipoic acid 600 mg qd orally for a mean period of 5 years. After stopping this treatment, 293 patients were switched to gabapentin (600-2400 mg/day), while 150 patients remained untreated because of no acute symptoms. In the untreated group, 110 (73%) patients developed neuropathic symptoms as soon as 2 weeks after the end of treatment with alpha-lipoic acid. In the group started on gabapentin, 131 (45%) patients had to stop taking the drug due to intolerable side effects. Among the patients treated with gabapentin 132 (45%) were responders on an average dose of 1200 mg/day, whereas 161 (55%) were nonresponders at gabapentin doses up to 2400 mg/day. These patients required an alternative treatment which consisted of pregabalin, carbamazepine, amitriptyline, tramadol, or morphine as monotherapy or in combination. The daily costs for alpha-lipoic acid were considerably lower than those for gabapentin or several frequently used drug combinations. The frequency of outpatient visits was 3.8 times per 3 months during the treatment period with alpha-lipoic acid, while it increased to 7.9 per 3 months after switching to gabapentin or the other pain medications. In conclusion, switching from long-term treatment with alpha-lipoic acid to central analgesic drugs such as gabapentin in painful diabetic neuropathy was associated with considerably higher rates of side effects, frequencies of outpatient visits, and daily costs of treatment. The pathogenic treatment option represents for the practicing diabetologist an effective, safe, and cost-effective treatment option for the majority of patients with diabetic polyneuropathy.

Painful diabetic neuropathy: epidemiology, natural history, early diagnosis, and treatment options

OBJECTIVE

To facilitate the clinician's understanding of the basis and treatment of painful diabetic neuropathy (PDN).

BACKGROUND

PDN is one of several clinical syndromes in patients with diabetic peripheral neuropathy (DPN) and presents a major challenge for optimal management.

METHODS

A systematic review of the literature was undertaken for articles specific to PDN, using Medline databases between 1966 and 2007.

RESULTS

The epidemiology of PDN has not been well established and on the basis of available data the prevalence of pain is 10% to 20% in patients with diabetes and from 40% to 50% in those with diabetic neuropathy. It has a significant impact on the quality of life and health care costs. Pathophysiologic mechanisms underlying PDN are similar to other neuropathic pain disorders and are broadly characterized as peripheral and central sensitization. The natural course of PDN is variable, with many patients experiencing spontaneous improvement and resolution of pain. 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. Quantifying neuropathic pain is difficult, especially for clinical trials, although this has improved recently with the development of neuropathic pain-specific tools, such as the Neuropathic Pain Questionnaire and the Neuropathic Pain Symptom Inventory. Current therapeutic options are limited to symptomatic treatment and are similar to other types of neuropathic pain.

CONCLUSIONS

A better understanding of the peripheral and central mechanisms resulting in PDN is likely to promote the development of more targeted and effective treatment.

Emerging drugs in neuropathic pain

Neuropathic pain is a personally devastating and costly condition affecting 3-8% of the population. Existing treatments have limited effectiveness and produce relatively frequent adverse effects. Preclinical research has identified many promising pharmacological targets; however, reliable predictors of success in humans remain elusive. At least 50 new molecular entities have reached clinical development including: glutamate antagonists, cytokine inhibitors, vanilloid-receptor agonists, catecholamine modulators, ion-channel blockers, anticonvulsants, opioids, cannabinoids, COX inhibitors, acteylcholine modulators, adenosine receptor agonists and several miscellaneous drugs. Eight drugs are in Phase III trials at present. Strategies that may show promise over existing treatments include topical therapies, analgesic combinations and, in future, gene-related therapies. Recent years have heralded an explosion of pharmaceutical development in neuropathic pain, reflecting advanced knowledge of neurobiology and a heightened perception of the commercial value of neuropathic pain therapeutics. In the interest of improving patient care, the authors recommend implementing comparative studies throughout the development process in order to demonstrate the increased value of novel agents.

The natural history of chronic painful peripheral neuropathy in a community diabetes population

AIMS

To examine the natural history of chronic painful diabetic neuropathy (CPDN).

METHODS

A cross-sectional study of 350 people with diabetes was performed during 1998-1999 to assess the prevalence of CPDN in the community. Fifty-six patients with CPDN were identified and were followed up an average of 5 years later.

RESULTS

From the original cohort, 12 patients had died and 14 had moved away or were unable to participate in the follow-up study. Thus 30 patients with CPDN [21 male, mean (SD) age 68.6 years (9.4), mean (SD) duration of diabetes 15.4 years (8.7)] were re-assessed. Seven (23%) had been pain free for at least 12 months and 23 continued to report neuropathic pain of similar quality and severity [total McGill Pain Questionnaire Score median (interquartile range) at follow-up 22 (16-39) vs. 20 (16-33) at baseline, P = 0.3; mean (SD) visual analogue scale (VAS) score for pain over the preceding 24 h 5.3 cm (2.9) vs. 4.6 cm (2.5) at baseline, P = 0.1]. Only 65% had ever received treatment for CPDN despite 96% (22/23) reporting pain to their physician; 43.5% had received antidepressants, 17.4% anticonvulsants, 39% opiates and 30% had tried complementary therapies.

CONCLUSIONS

The neuropathic pain of CPDN can resolve completely over time in a minority (23%). In those in whom painful neuropathic symptoms had persisted over 5 years, no significant improvement in pain intensity was observed. Despite the improvement in treatment modalities for chronic pain in recent years, patients with CPDN continue to be inadequately treated.

Neuropathic pain: a practical guide for the clinician

Neuropathic pain, caused by various central and peripheral nerve disorders, is especially problematic because of its severity, chronicity and resistance to simple analgesics. The condition affects 2%-3% of the population, is costly to the health care system and is personally devastating to the people who experience it. The diagnosis of neuropathic pain is based primarily on history (e.g., underlying disorder and distinct pain qualities) and the findings on physical examination (e.g., pattern of sensory disturbance); however, several tests may sometimes be helpful. Important pathophysiologic mechanisms include sodium-and calcium-channel upregulation, spinal hyperexcitability, descending facilitation and aberrant sympathetic-somatic nervous system interactions. Treatments are generally palliative and include conservative nonpharmacologic therapies, drugs and more invasive interventions (e.g., spinal cord stimulation). Individualizing treatment requires consideration of the functional impact of the neuropathic pain (e.g., depression, disability) as well as ongoing evaluation, patient education, reassurance and specialty referral. We propose a primary care algorithm for treatments with the most favourable risk-benefit profile, including topical lidocaine, gabapentin, pregabalin, tricyclic antidepressants, mixed serotonin-norepinephrine reuptake inhibitors, tramadol and opioids. The field of neuropathic pain research and treatment is in the early stages of development, with many unmet goals. In coming years, several advances are expected in the basic and clinical sciences of neuropathic pain, which will provide new and improved therapies for patients who continue to experience this disabling condition.

Diabetic peripheral neuropathic pain: clinical and quality-of-life issues

Diabetic peripheral neuropathy (DPN) is estimated to be present in 50% of people living with diabetes mellitus (DM). Comorbidities of DM, such as macrovascular and microvascular changes, also Interact with DPN and affect its course. In patients with DM, DPN Is the leading cause of foot ulcers, which in turn are a major cause of amputation in the United States. Although most patients with DPN do not have pain, approximately 11% of patients with DPN have chronic, painful symptoms that diminish quality of life, disrupt sleep, and can lead to depression. Despite the number of patients affected by DPN pain, little consensus exists about the pathophysiology, best diagnostic tools, and primary treatment choices. This article reviews the current knowledge about and presents recommendations for diagnostic assessment of DPN pain based on a review of the literature.

Zonisamide in the treatment of painful diabetic neuropathy: a randomized, double-blind, placebo-controlled pilot study

BACKGROUND

Painful diabetic neuropathy is a form of neuropathic pain frequently encountered as a complication of diabetes mellitus types I and II. Pharmacotherapy is one modality of treatment for this distressing and often disabling condition, but there is no medication available that consistently provides adequate pain relief with acceptable safety and tolerability. Tricyclic antidepressants, certain antiepileptic drugs, and opioids have been shown in randomized, controlled trials to be of benefit in painful diabetic neuropathy, although none has Food and Drug Administration (FDA)-approved labeling for this indication.

STUDY OBJECTIVE

To analyze the safety and efficacy of zonisamide in the treatment of painful diabetic neuropathy. This pilot study is the first randomized, controlled trial of zonisamide for the treatment of any neuropathic pain disorder.

STUDY DESIGN

Forty-two patients 18-80 years of age with type I or type II diabetes mellitus and at least a 3-month history of painful diabetic neuropathy were screened in the study, and 25 were randomized to zonisamide (N = 13) or placebo (N = 12). The study drug was titrated over a 6-week period and continued at a fixed dosage for a 6-week maintenance period. The mean dosage of zonisamide for the maintenance phase was 540 mg/day.

OUTCOME MEASURES

Patients kept a daily log of their pain using both a 0-100 mm visual analog scale and a 0-10 Likert scale.

RESULT

Pain scores on both the visual analog scale and the Likert scale decreased more for the zonisamide group compared with the placebo group, regardless of whether the comparison was made for the intent-to-treat population, the population that entered the maintenance phase, or the completer population, but these differences did not reach statistical significance. Tolerability of zonisamide was only fair in this study, which had a high number of dropouts from the zonisamide group.

CONCLUSION

A larger randomized, controlled trial is needed to establish the efficacy and tolerability of zonisamide for painful diabetic neuropathy.

Electrical spinal cord stimulation in the long-term treatment of chronic painful diabetic neuropathy

AIMS

Electrical spinal cord stimulation (ESCS) is a technique for the management of chronic painful diabetic neuropathy (CPDN) affecting the lower limbs. We assessed the efficacy and complication rate of ESCS implanted at least 7 years previously in eight patients.

METHODS

After a trial period of percutaneous stimulation, eight male patients had been implanted with a permanent system. Mean age at implantation was 53.5 years and all patients were insulin treated with stage 3 severe disabling CPDN of at least 1 year's duration. The ESCS was removed from one patient at 4 months because of system failure and one patient died 2 months after implantation from a myocardial infarction.

RESULTS

Six patients were reviewed a mean of 3.3 years post-implantation. With the stimulator off, McGill pain questionnaire (MPQ) scores (a measure of the quality and severity of pain) were similar to MPQ scores prior to ESCS insertion. Pain scores (visual analogue scale) were measured with the stimulator off and on, respectively: background pain [74.5 (63-79) mm vs. 25 (17-33) mm, median (interquartile range), P = 0.03), peak pain (85 (80-92) mm vs. 19 (11-47) mm, P = 0.03]. There were two further cardiovascular deaths (these patients had continued pain relief) and the four surviving patients were reassessed at 7.5 (range 7-8.5) years: background pain [73 (65-77) mm vs. 33 (28-36) mm, median (interquartile range)], peak pain [86 (81-94) mm vs. 42 (31-53) mm]. Late complications (> 6 months post-insertion) occurred in two patients; electrode damage secondary to trauma requiring replacement (n = 1), and skin peeling under the transmitter site (n = 1). One patient had a second electrode implanted in the cervical region which relieved typical neuropathic hand pains.

CONCLUSIONS

ESCS can continue to provide significant pain relief over a prolonged period of time with little associated morbidity.

Efficacy of Oxcarbazepine in the Treatment of Painful Diabetic Neuropathy

OBJECTIVES

To evaluate the safety, tolerability, and efficacy of oxcarbazepine in the treatment of painful diabetic neuropathy.

METHODS

This was an open-label, 9-week trial, consisting of a 1-week prospective Screening Phase followed by an 8-week Treatment Phase. Treatment with oxcarbazepine was initiated at 150 mg/day, and the daily dose was doubled on a weekly basis and titrated to tolerability over 4 weeks, up to 1200 mg/day. This was followed by a 4-week fixed-dose Maintenance Phase, during which patients were maintained on oxcarbazepine at 1200 mg/day or highest tolerated dose. The primary efficacy variable was the change in the weekly pain rating assessed on the Visual Analog Scale (VAS) of the short-form McGill Pain Questionnaire between the Screening Phase and the Treatment Phase. All analyses were performed on the intent-to-treat population.

RESULTS

Thirty patients were enrolled in the trial. The mean daily oxcarbazepine dose during the Maintenance Phase was 814 mg. The mean VAS score dropped from 66.3 during the Screening Phase to 34.3 at the end of the trial (P = 0.0001), for a mean reduction of 48.3%. In addition, there were significant improvements in the total pain score and present pain intensity. Oxcarbazepine was well tolerated, with the most common adverse events consisting of drowsiness and dizziness.

DISCUSSION

The results suggest that oxcarbazepine administered as monotherapy is an efficacious and safe option for the symptomatic treatment of pain associated with symmetrical diabetic neuropathy. These results will need to be confirmed in large, double-blind, placebo-controlled, randomized clinical trials.

Static magnetic field therapy for symptomatic diabetic neuropathy: a randomized, double-blind, placebo-controlled trial

OBJECTIVE

To determine if constant wearing of multipolar, static magnetic (450G) shoe insoles can reduce neuropathic pain and quality of life (QOL) scores in symptomatic diabetic peripheral neuropathy (DPN).

DESIGN

Randomized, placebo-control, parallel study.

SETTING

Forty-eight centers in 27 states.

PARTICIPANTS

Three hundred seventy-five subjects with DPN stage II or III were randomly assigned to wear constantly magnetized insoles for 4 months; the placebo group wore similar, unmagnetized device.

INTERVENTION

Nerve conduction and/or quantified sensory testing were performed serially.

MAIN OUTCOME MEASURES

Daily visual analog scale scores for numbness or tingling and burning and QOL issues were tabulated over 4 months. Secondary measures included nerve conduction changes, role of placebo, and safety issues. Analysis of variance (ANOVA), analysis of covariance (ANCOVA), and chi-square analysis were performed.

RESULTS

There were statistically significant reductions during the third and fourth months in burning (mean change for magnet treatment, -12%; for sham, -3%; P<.05, ANCOVA), numbness and tingling (magnet, -10%; sham, +1%; P<.05, ANCOVA), and exercise-induced foot pain (magnet, -12%; sham, -4%; P<.05, ANCOVA). For a subset of patients with baseline severe pain, statistically significant reductions occurred from baseline through the fourth month in numbness and tingling (magnet, -32%; sham, -14%; P<.01, ANOVA) and foot pain (magnet, -41%; sham, -21%; P<.01, ANOVA).

CONCLUSIONS

Static magnetic fields can penetrate up to 20mm and appear to target the ectopic firing nociceptors in the epidermis and dermis. Analgesic benefits were achieved over time.

Potential mechanisms of neuropathic pain in diabetes

Abnormal sensations and pain are features of approximately 10% of all cases of diabvetic neuropathy and can cause marked diminution in the quality of life for these patients. The quality and distribution of pain are variable, although descriptions of burning pain in the hands and feet are commonly reported. Like other neuropathic pain states, painful diabetic neuropathy has an unknown pathogenesis and, in many cases, is not alleviated by nonsteriodal anti-inflammatory drugs or opiates. In the last decase, a number of behavioral and physiologic studies have revealed indices of sensory dysfunction in animal models of diabetes. These include hyperalgesia to mechanical and noxious chemical stimuli and allodynia to light touch. Animal models of painful diabetic neuropathy have been used to investigate the therapeutic potential of a range of experimental agents and also to explore potential etiologic mechanisms. There is relatively little evidence to suggest that the peripheral sensory nerves of diabetic rodents exhibit spontaneous activity or increased responsiveness to peripheral stimuli. Indeed, the weight of eveidence suggests that sensory input to the spinal cord is decreased rather than increased in diabetic rodents. Aberrant spinal or supraspinal modulation of sensory processing may therefore be involved in generating allodynia and hyperalgesia in these models. Studies have supported a role for spinally mediated hyeralgesia in diabetic rats that may reflect either a response to diminished peripheral input or a consequence of hyperglycemia on local or descending modulatory systems. Elucidating the affects of diabetes on spinal sensory processing may assist development of novel therapeutic strategies for preventing and alleviating painful diabetic neuropathy.

Understanding the impact of painful diabetic neuropathy

Painful neuropathy is a common and often distressing complication of diabetes. It has considerable impact on the social and psychological well-being of affected individuals. There are two distinct forms of painful neuropathy: an acute and self-limiting form that resolves within a year or a chronic form that can go on for years. There are now a number of drugs available for the treatment of neuropathic pain. However, some may fail to respond to these drugs or may have unacceptable adverse side effects. When this is the case, the patient's quality of life can be severely affected. Health care professionals need to assess the full impact of painful neuropathy. In this article we review a number of instruments that are used to assess the severity of painful neuropathy and its impact on the quality of life.

Trends in opioid use for chronic neuropathic pain: a survey of patients pursuing enrollment in clinical trials

PURPOSE

Clinical trials suggest that opioids relieve neuropathic pain and decrease pain-related disability. We conducted a pilot study of current prescribing trends and patients' attitudes towards opioids for neuropathic pain.

METHODS

A patient questionnaire was completed by individuals pursuing enrollment in neuropathic pain clinical trials at our facility.

RESULTS

Of 154 patients with diabetic neuropathy (55.2%), postherpetic neuralgia (29.9%), idiopathic peripheral neuropathy (9.7%) and other neuropathies (5.2%), 73.4% complained of inadequate pain control, the mean pain duration was 4.7 (SD = 4.4) yr and the mean pain intensity (0-10) was 7.7 (SD = 2.3). In this group, 40.9% had never tried opioids and 24.7% had never tried any opioids, tricyclic antidepressants or anticonvulsants. Only 9.7% were receiving long-acting opioids or "around the clock" dosing whereas 25.3% were receiving opioids on an "as needed" basis. Opioids combined with tricyclic antidepressants and/or anticonvulsants were used in 11.0%. Fear of addiction and adverse effects were expressed by 31.8% and 46.8% respectively.

CONCLUSION

These data suggest that barriers to opioid therapy for neuropathic pain include patients', and possibly physicians', fears of addiction and adverse effects, which are exaggerated in light of current evidence. The merits of continuous treatment with sustained-release opioids, "as needed" dosing with short-acting preparations, or combining opioids with other agents are discussed. Continued research and communication between health professionals, law enforcement officials and legislators is vital in order to facilitate appropriate opioid use which has a minimal negative impact on the public yet optimally benefits individuals who suffer from disabling neuropathic pain.

Epidemiology and impact on quality of life of postherpetic neuralgia and painful diabetic neuropathy

OBJECTIVE

This article reviews the prevalence, risk factors, natural history, and impact on quality of life of painful diabetic neuropathy (PDN) and postherpetic neuralgia (PHN).

DISCUSSION

Diabetes mellitus afflicts more than 14 million persons in the U.S. An estimated 20% to 24% of these persons experience PDN. Data on risk factors for PDN are limited, but duration of diabetes mellitus and poor glycemic control are probably important factors. Painful diabetic neuropathy may interfere with general activity, mood, mobility, work, social relations, sleep, leisure activities, and enjoyment of life. Herpes zoster strikes an estimated 800,000 persons each year in the U.S., most of whom are elderly or immunosuppressed. Using pain at 3 months after rash onset as a definition of PHN, between 25% and 50% of adults older than 50 years develop PHN, depending on early antiviral therapy for herpes zoster. Increasing age, greater pain and rash severity, greater degree of sensory impairment, and psychological distress are risk factors for PHN. Postherpetic neuralgia may cause fatigue, insomnia, depression, anxiety, interference with social roles and leisure activity, and impaired basic and instrumental activities of daily living.

CONCLUSIONS

Both conditions are common complications of their underlying disorders and can profoundly diminish the quality of life of affected persons.

Diabetic neuropathic cachexia and acute bilateral cataract formation following rapid glycaemic control in a newly diagnosed type 1 diabetic patient

In patients with Type 1 diabetes mellitus (DM), the development of complications within the first few years of diagnosis is very unusual and the development of complications within weeks of commencement of insulin therapy is exceptional. Diabetic neuropathic cachexia, unlike the other more common neuropathies associated with diabetes, is a rare form of peripheral neuropathy characterized by profound weight loss, painful dysaesthesias over the limbs and trunk with spontaneous resolution usually occurring within a year. The morphologically distinct diabetic or metabolic cataract in patients with newly diagnosed Type 1 DM is also a rare complication. We describe the first case of a young man with newly diagnosed Type 1 DM who developed these two rare complications within 3 months of diagnosis and insulin therapy commencement. Rapid development of complications in this patient raises two possibilities, i.e. a probable link between the pathophysiology of these two complications following rapid glycaemic control, and a subset of patients with unusual susceptibility to complications. We re-emphasize the need for vigilant monitoring of complications in young diabetic patients, even in the first few years of their disease. In particular, young patients with visual impairment should be evaluated carefully for evidence of treatable eye complications.

Painful diabetic neuropathy

Chronic painful diabetic neuropathy causes symptoms that can last for many years and severely impair the quality of life of affected patients. This review describes the epidemiology, pathophysiology and treatment of chronic neuropathic pain. Particular emphasis is placed on a comprehensive review of the management of painful symptoms through a detailed review of the published literature using a variety of databases particularly Medline and EMBASE.

Painful diabetic neuropathy

Chronic painful diabetic neuropathy can cause a variety of challenges, particularly in successful treatment. The pain, which can last for years, can severely impair quality of life. Management is difficult, although the careful use of drugs can be significantly beneficial. Tricyclic and anticonvulsant drugs may be effective, with a variety of drugs available as second line agents. Newer non-drug systems such as electrical spinal cord stimulation represent exciting possibilities for the future management of this most difficult diabetic syndrome.

Mexiletine. A review of its therapeutic use in painful diabetic neuropathy

Mexiletine is an orally active local anaesthetic agent which is structurally related to lidocaine (lignocaine) and has been used for alleviating neuropathic pain of various origins. Mexiletine has been evaluated in several randomised, placebo-controlled trials in patients with painful diabetic neuropathy. The drug decreased mean visual analogue scale (VAS) pain ratings in all studies that used this measure, although in only 2 studies was this effect significantly greater than the often substantial responses seen with placebo. The clinical significance of these decreases is not clear. Statistically significant (vs placebo) reductions in VAS pain ratings were observed in 16 patients receiving mexiletine 10 mg/kg/day for 10 weeks in 1 study and in nocturnal (but not diurnal) pain in 31 patients receiving mexiletine 675 mg/day for 3 weeks in another. Retrospective analysis of another study revealed that mexiletine recipients (225 to 675 mg/day) who described their pain as stabbing, burning or formication on the pain-rating-index-total instrument of the McGill Pain Questionnaire, experienced statistically significant reductions in VAS pain scores after 5 weeks, compared with placebo recipients. Mexiletine generally did not have a significant influence on the quality of sleep in patients with diabetic neuropathy. In Japanese patients, statistically significant reductions in subjective pain ratings were achieved with mexiletine 300 mg/day in 1 study and with 450 mg/day in a further study. In controlled trials, the frequency of adverse events in patients receiving mexiletine for painful diabetic neuropathy ranged from 13.5 to 50%. Gastrointestinal complaints, of which nausea was the most frequent, were the most common adverse events in mexiletine recipients. Central nervous system complaints were uncommon, but included: sleep disturbance, headache, shakiness, dizziness and tiredness. Serious cardiac arrhythmias have not been reported in patients receiving mexiletine for painful diabetic neuropathy; however, transient tachycardia and palpitations have been reported. There are significant differences in the metabolism of mexiletine between people who have cytochrome P450 2D6 [CYP2D6; extensive metabolisers (EMs)] and those who lack this isoenzyme [poor metabolisers (PMs)]. EMs, but not PMs, are susceptible to drug interactions between mexiletine and drugs that inhibit CYP2D6 (e.g. quinidine). Moreover, mexiletine inhibits CYP2D6-mediated metabolism of metoprolol and cytochrome P450 1A2-mediated metabolism of theophylline. Phenytoin and rifampicin (rifampin) induce the metabolism of mexiletine. Clearance of mexiletine is impaired in patients with hepatic, but not renal, dysfunction. Hence, dosage adjustments may be necessary in patients with liver disease.

CONCLUSIONS

Tricyclic antidepressants (TCAs) are the agents of choice for painful diabetic neuropathy; however, they are ineffective in approximately 50% of patients and are generally not well tolerated. Mexiletine is an alternative agent for the treatment of painful diabetic neuropathy in patients who have not had a satisfactory response to, or cannot tolerate, TCAs and/or other drugs.

Acupuncture for the treatment of chronic painful peripheral diabetic neuropathy: a long-term study

Forty-six diabetic patients with chronic painful peripheral neuropathy were treated with acupuncture analgesia to determine its efficacy and long-term effectiveness. Twenty-nine (63%) patients were already on standard medical treatment for painful neuropathy. Patients initially received up to six courses of classical acupuncture analgesia over a period of 10 weeks, using traditional Chinese Medicine acupuncture points. Forty-four patients completed the study with 34 (77%) showing significant improvement in their primary and/or secondary symptoms (P < 0.01). These patients were followed up for a period of 18-52 weeks with 67% were able to stop or reduce their medications significantly. During the follow-up period only eight (24%) patients required further acupuncture treatment. Although 34 (77%) patients noted significant improvement in their symptoms, only seven (21%) noted that their symptoms cleared completely. All the patients but one finished the full course of acupuncture treatment without reported or observed side effects. There were no significant changes either in the peripheral neurological examination scores, VPT or in HbA1c during the course of treatment. These data suggest that acupuncture is a safe and effective therapy for the long-term management of painful diabetic neuropathy, although its mechanism of action remains speculative.

The cost of diabetic neuropathy

Little information is available as to the exact financial cost of the clinical features of diabetic neuropathy. At least 20% of diabetic patients have a neuropathic problem consisting of either sensory pain and discomfort, foot ulceration or impotence. This represents a large load of clinical work in any diabetes service. Such patients should be offered thorough and sympathetic clinical facilities, from careful diagnosis and assessment through to treatment and counselling, to allow them to accept, and hopefully obtain improvement in, what is essentially an incurable clinical situation. Similarly, the emotional and financial costs to the patients of such a chronic condition have not been adequately assessed. It seems reasonable to suggest that such costs are high, and it is a general impression that patients with this problem do not receive adequate time and attention in many busy diabetes services.

Role of electrophysiological studies in diabetic neuropathy

Electrophysiological studies are a reproducible and noninvasive method of assessing peripheral nerve function. The sensitivity of these methods has been validated in population-based and clinical studies, and the variability of test results is typically lower than with other noninvasive tests of nerve function. It has been recommended that standardized procedures including temperature control and equipment calibration be utilized with electrophysiological testing. The failure to detect significant changes in nerve conduction studies from clinical studies may be due to poor standardization of technique and inadequate sample size to detect differences. Baseline results from a multicenter, randomized trial indicate that different electrophysiological measures are highly correlated and reproducible. This and future studies that incorporate standardized techniques and an adequate sample size should be able to detect significant differences between treatments and identify effective therapeutic interventions for diabetic neuropathy.

A prospective study of painful symptoms, small-fibre function and peripheral vascular disease in chronic painful diabetic neuropathy

Fifty diabetic patients with chronic painful sensorimotor neuropathy were studied prospectively to clarify the natural history of this condition and the roles of small-fibre damage and concomitant peripheral vascular disease (PVD). Initially, 30 patients had no significant PVD (ankle:brachial Doppler ratio > 1.0). Pain was assessed using a visual analogue scale (0-10 cm), and small-fibre function by thermal limen (TL), heat-pain threshold (HPT), and weighted pinprick threshold (PPT). At follow-up, on average 3.6 years later (range 3.0-4.1), 11 patients had died (6 with PVD) and contact had been lost with 6. Pain scores fell in subjects without PVD (n = 24; median (range), from 4.8 (0.5-10.0) to 2.0 (0.0-9.2) cm, p < 0.001) and also in those with PVD (n = 9; from 5.1 (2.0-8.2) to 2.1 (0.0-8.0) cm, p < 0.05). Seven patients (5 without PVD) became painfree; at presentation, these 7 patients had experienced pain for a shorter period of time. Despite this symptomatic improvement, small-fibre function generally deteriorated in both groups, with significant worsening (p < 0.05) of HPT and PPT in patients without PVD, and in HPT and TL in patients with PVD. Neuropathic pain therefore tends to improve with time and can resolve completely. By contrast, small-fibre function continues to deteriorate, indicating that these peripheral measures do not predict the evolution of painful symptoms. The presence or absence of PVD does not appear to affect the natural history of neuropathic pain or its symptomatology.

Mechanical hyperalgesia in streptozotocin-diabetic rats is not sympathetically maintained

It has been suggested that the mechanism underlying the pain that occurs in patients with diabetic neuropathy may be similar to that mediating sympathetically maintained pain (SMP), such as occurs in patients with reflex sympathetic dystrophy. To evaluate this suggestion we have examined a model of diabetes mellitus, the streptozotocin-diabetic (STZ-D) rat, for features characteristic of SMP. We demonstrate that the decrease in nociceptive threshold observed in the STZ-D rat is not attenuated by chemical sympathectomy nor exacerbated by intradermal injection of norepinephrine (NE). In addition, the NE content is markedly decreased in the skin of the STZ-D rat. These results suggest that altered nociceptive thresholds associated with diabetic neuropathy are not sympathetically maintained.

A 12-month randomized controlled study of the aldose reductase inhibitor ponalrestat in patients with chronic symptomatic diabetic neuropathy

The effects of the aldose reductase inhibitor ponalrestat (600 mg day-1) on sensory, electrophysiological, and autonomic function were examined in 50 patients with chronic symptomatic, distal symmetrical diabetic neuropathy in a 52-week randomized, double-blind, parallel-group, placebo-controlled, single-centre study. In an endeavour to identify patients with a degree of neuropathy potentially amenable to pharmacological intervention, a minimum conduction velocity of 30 m s-1 was set for the peroneal motor nerve. At 52 weeks, no significant differences were observed between the ponalrestat and placebo groups in motor (ulnar, median, and peroneal) or sensory (ulnar and radial) nerve conduction velocities, vibration perception thresholds, adjectival symptom scores or tests of autonomic function (mean electrocardiographic R-R interval variability on deep breathing and orthostatic blood pressure response). Ponalrestat was clinically well tolerated and had no significant effect on glycaemic control. The lack of beneficial effects of ponalrestat may in part reflect the advanced stage of the neuropathic process in patients with established symptomatic disease, and the poor reproducibility of current neurophysiological techniques. Firmer knowledge of clinico-pathological correlates allied to improved non-invasive neurophysiological measurement techniques should facilitate the selection of patients for future therapeutic trials in diabetic neuropathy.

Discrimination between painful and painless diabetic neuropathy based on testing of large somatic nerve and sympathetic nerve function

The syndromes of painful diabetic neuropathy and painless foot ulceration are distinct clinical entities. To investigate whether there is a pattern of nerve fibre involvement that could clearly discriminate between them, we have studied three groups of diabetic patients, 19 with painful neuropathy, 14 with painless foot ulceration, and 19 with no clinical neuropathy. Large somatic nerve fibre function was assessed by nerve conduction studies and vibration thresholds, small somatic nerve function by cooling and warming thresholds, the parasympathetic system by heart-rate dependent cardiac autonomic reflexes, and the sympathetic system by postural drop in blood pressure and plasma noradrenaline (supine and erect). Normal ranges were obtained from 25 age-matched healthy subjects. Painful neuropathy was characterized by uniform dysfunction of small somatic fibres and preserved sympathetic nerve activity (plasma noradrenaline) with a wide range of large somatic fibre and autonomic reflex abnormalities. By contrast, in painless foot ulceration there was universal severe dysfunction of all nerve fibre populations. Discriminant analysis identified peroneal motor conduction velocity as the best single variable for distinguishing between painful and painless neuropathy (81% of cases). A combination of peroneal motor conduction velocity with vibration threshold and plasma noradrenaline discriminated completely between the two clinical syndromes. These findings suggest that the key differences between painful and painless diabetic neuropathy are in large somatic and sympathetic fibre function.