Influence of neuropathy on the microvascular response to local heating in the human diabetic foot

Effect of Exercise Volume on Plantar Microcirculation and Tissue Hardness in People With Type 2 Diabetes

Objective: Exercise has been reported to be beneficial for people with type 2 diabetes (T2DM), but exercise, especially weight-bearing exercise, may increase the risk of diabetic foot ulcers (DFUs). This study aimed to explore the associations between different volumes of weight-bearing physical activities and plantar microcirculation and tissue hardness in people with T2DM.

Methods: 130 elderly people with T2DM were enrolled for this cross-sectional study. They were classified into the high exercise volume group and the low exercise volume group based on their weekly energy expenditure (metabolic equivalents per week) in the past year. Weekly energy expenditure was calculated using the International Physical Activity Questionnaire and the Compendium of Physical Activities. The plantar oxygen saturation (SO₂) and soft tissue hardness of each participant’s right foot were measured.

Results: A total of 80 participants completed the trial. The average exercise energy expenditure of the high exercise volume group and the low exercise volume group were significantly different (p < 0.05). The results showed that the SO₂ of the high exercise volume group (67.25 ± 6.12%) was significantly higher than the low exercise volume group (63.75 ± 8.02%, p < 0.05). The plantar tissue hardness of the high exercise volume group was lower than the low exercise volume group in the big toe, midfoot and hindfoot regions (p < 0.05).

Conclusion: This study demonstrates that higher volumes of exercise are associated with better plantar microcirculation and lower plantar tissue hardness in people with T2DM. The findings of this study indicate that weight-bearing exercise may not increase risk of developing diabetic foot ulcers.

Diabetic Peripheral Neuropathy: Diagnosis and Treatment

BACKGROUND

Diabetic peripheral neuropathy (DPN) is traditionally divided into large and small fibre neuropathy (SFN). Damage to the large fibres can be detected using nerve conduction studies (NCS) and often results in a significant reduction in sensitivity and loss of protective sensation, while damage to the small fibres is hard to reliably detect and can be either asymptomatic, associated with insensitivity to noxious stimuli, or often manifests itself as intractable neuropathic pain.

OBJECTIVE

To describe the recent advances in both detection, grading, and treatment of DPN as well as the accompanying neuropathic pain.

METHODS

A review of relevant, peer-reviewed, English literature from MEDLINE, EMBASE and Cochrane Library between January 1st 1967 and January 1st 2020 was used.

RESULTS

We identified more than three hundred studies on methods for detecting and grading DPN, and more than eighty randomised-controlled trials for treating painful diabetic neuropathy.

CONCLUSION

NCS remains the method of choice for detecting LFN in people with diabetes, while a gold standard for the detection of SFN is yet to be internationally accepted. In the recent years, several methods with huge potential for detecting and grading this condition have become available including skin biopsies and corneal confocal microscopy, which in the future could represent reliable endpoints for clinical studies. While several newer methods for detecting SFN have been developed, no new drugs have been accepted for treating neuropathic pain in people with diabetes. Tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors and anticonvulsants remain first line treatment, while newer agents targeting the proposed pathophysiology of DPN are being developed.

Chronic limb-threatening ischemia could benefit from growth hormone therapy for wound healing and limb salvage

Revascularization for chronic limb-threatening ischemia (CLTI) is necessary to alleviate symptoms and wound healing. When it fails or is not possible, there are few alternatives to avoid limb amputation in these patients. Although experimental studies with stem cells and growth factors have shown promise, clinical trials have demonstrated inconsistent results because CLTI patients generally need arteriogenesis rather than angiogenesis. Moreover, in addition to the perfusion of the limb, there is the need to improve the neuropathic response for wound healing, especially in diabetic patients. Growth hormone (GH) is a pleiotropic hormone capable of boosting the aforementioned processes and adds special benefits for the redox balance. This hormone has the potential to mitigate symptoms in ischemic patients with no other options and improves the cardiovascular complications associated with the disease. Here, we discuss the pros and cons of using GH in such patients, focus on its effects on peripheral arteries, and analyze the possible benefits of treating CLTI with this hormone.

The association between diabetes and dermal microvascular dysfunction non-invasively assessed by laser Doppler with local thermal hyperemia: a systematic review with meta-analysis

Background/Introduction

Diabetes and cardiovascular disease develop in concert with metabolic abnormalities mirroring and causing changes in the vasculature, particularly the microcirculation. The microcirculation can be affected in different parts of the body of which the skin is the most easily accessible tissue.

Purpose

The association between diabetes and dermal microvascular dysfunction has been investigated in observational studies. However, the strength of the association is unknown. Therefore we conducted a systematic review with meta-analysis on the association between diabetes and dermal microvascular dysfunction as assessed by laser Doppler/laser speckle contrast imaging with local thermal hyperaemia as non-invasive indicator of microvascular functionality.

Methods

PubMed and Ovid were  systematically searched for eligible studies through March 2015. During the first selection, studies were included if they were performed in humans and were related to diabetes or glucose metabolism disorders and to dermal microcirculation. During the second step we selected studies based on the measurement technique, measurement location (arm or leg) and the inclusion of a healthy control group. A random effects model was used with the standardised mean difference as outcome measure. Calculations and imputation of data were done according to the Cochrane Handbook.

Results

Of the 1445 studies found in the first search, thirteen cross-sectional studies were included in the meta-analysis, comprising a total of 857 subjects. Resting blood flow was similar between healthy control subjects and diabetes patients. In contrast, the microvascular response to local skin heating was reduced in diabetic patients compared to healthy control subjects [pooled effect of −0.78 standardised mean difference (95% CI −1.06, −0.51)]. This effect is considered large according to Cohen’s effect size definition. The variability in effect size was high (heterogeneity 69%, p < 0.0001). However, subgroup analysis revealed no difference between the type and duration of diabetes and other health related factors, indicating that diabetes per se causes the microvascular dysfunction.

Conclusion

Our meta-analysis shows that diabetes is associated with a large reduction of dermal microvascular function in diabetic patients. The local thermal hyperaemia methodology may become a valuable non-invasive tool for diagnosis and assessing progress of diabetes-related microvascular complications, but standardisation of the technique and quality of study conduct is urgently required.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0487-1) contains supplementary material, which is available to authorized users.

Advanced glycation end products assessed by skin autofluorescence: a new marker of diabetic foot ulceration

BACKGROUND

Accumulation of advanced glycation end products (AGEs) may contribute to diabetic foot ulceration (DFU). Our goal was to determine whether AGEs measurement by skin autofluorescence (SAF) would be an additional marker for DFU management.

PATIENTS AND METHODS

We performed SAF analysis in 66 patients with a history of DFU prospectively included and compared the results with those of 84 control patients with diabetic peripheral neuropathy without DFU. We then assessed the prognostic value of SAF levels on the healing rate in the DFU group.

RESULTS

Mean SAF value was significantly higher in the DFU group in comparison with the control group, even after adjustment for other diabetes complications (3.2±0.6 arbitrary units vs. 2.9±0.6 arbitrary units; P=0.001). In the DFU group, 58 (88%) patients had an active wound at inclusion. The mean DFU duration was 14±13 weeks. The healing rate was 47% after 2 months of appropriate foot care. A trend for a correlation between SAF levels and healing time in DFU subjects was observed but was not statistically significant (P=0.06).

CONCLUSIONS

Increased SAF levels are associated with neuropathic foot complications in diabetes. Use of SAF measurement to assess foot vulnerability and to predict DFU events in high-risk patients appears to be promising.

Streptozotocin-induced diabetes differentially affects sympathetic innervation and control of plantar metatarsal and mesenteric arteries in the rat

In humans neural control of arterial vessels supplying skin in the extremities is particularly vulnerable to the effects of diabetes. Here the streptozotocin (STZ) rat model of type 1 diabetes was used to compare effects on neurovascular function in plantar metatarsal arteries (PMAs), which supply blood to skin of hind paw digits, with those in mesenteric arteries (MAs). Twelve weeks after STZ (60 mg/kg ip), wire myography was used to assess vascular function. In PMAs, lumen dimensions were unchanged but both nerve-evoked contractions and sensitivity to α(1) (phenylephrine, methoxamine)- and α(2) (clonidine)-adrenoceptor agonists were reduced. The density of perivascular nerve fibers was also reduced by ~25%. These changes were not observed in PMAs from STZ-treated rats receiving either a low dose of insulin that did not greatly reduce blood glucose levels or a high dose of insulin that markedly reduced blood glucose levels. In MAs from STZ-treated rats, nerve-evoked increases in force did not differ from control but, because lumen dimensions were ~20% larger, nerve-evoked increases in effective transmural pressure were smaller. Increases in effective transmural pressure produced by phenylephrine or α,β-methylene ATP in MAs from STZ-treated rats were not smaller than control, but the density of perivascular nerve fibers was reduced by ~10%. In MAs, the increase in vascular dimensions is primarily responsible for reducing effectiveness of nerve-evoked constrictions. By contrast, in PMAs decreases in both the density of perivascular nerve fibers and the reactivity of the vascular muscle appear to explain impairment of neurovascular transmission.

Cutaneous structural and biochemical correlates of foot complications in high-risk diabetes

OBJECTIVE

Impairment of skin quality may contribute to diabetic foot ulceration (DFU). Our goal was to determine whether high-risk patients exhibited specific skin structural and metabolic deficits that could predispose to foot complications.

RESEARCH DESIGN AND METHODS

A total of 46 patients comprising 9 diabetic control subjects, 16 with diabetic peripheral neuropathy (DPN) alone, and 21 with recurrent DFUs (including 9 with Charcot neuroarthropathy [CNA]) were recruited and compared with 14 nondiabetic control (NDC) subjects. DPN was assessed using the Michigan Neuropathy Screening Instrument (MNSI). Skin punch biopsies (3 mm) were performed on upper and lower leg skin for measurements of intraepidermal nerve fiber density (IENFD), structural analysis, type 1 procollagen abundance, tissue degrading matrix metalloproteinases (MMPs), and poly(ADP-ribose) (PAR) immunoreactivity.

RESULTS

MNSI scores were comparable across DPN groups. IENFD was decreased by diabetes and DPN but did not differ between neuropathic groups. Skin structural deficit scores were elevated in all neuropathic subjects, particularly in the DFU group. Type 1 procollagen abundance was reduced in DFU subjects 387 ± 256 units (mean ± 1 SD) compared with NDC subjects (715 ± 100, P < 0.001). MMP-1 and MMP-2 were activated by diabetes. PAR immunoreactivity was increased in DFU (particularly in the CNA group; P < 0.01) compared with other DPN subjects.

CONCLUSIONS

Increased PAR, reduced type 1 procollagen abundance, and impaired skin structure are associated with foot complications in diabetes. The potential of therapies that improve skin quality to reduce DFU needs to be investigated.

New developments in diabetic neuropathy

PURPOSE OF REVIEW

Diabetic neuropathy is a debilitating consequence of type 1 and 2 diabetes. Hyperglycemia disrupts the normal function of neurons and their supporting glia at multiple levels. The complexity of this complication, combined with difficulties of delivering therapy to sensory, sympathetic and parasympathetic neurons, contributes to the intractability of this serious diabetic complication. This review summarizes recent reviews examining the state of research on and treatment of diabetic neuropathy and highlights areas of clinical and basic research that may yield new diagnostic and treatment options.

RECENT FINDINGS

Recent reviews summarize the effects of hyperglycemia on the peripheral nervous system as well as diagnosis and treatment of patients with diabetic neuropathy. Advances in the analysis of intraepidermal fiber densities could shorten the time course of clinical trials and extend data analyses to include sympathetic as well as sensory information. Unchecked glucose-mediated oxidative stress and advanced glycation endproduct signaling through receptors for advanced glycation endproducts are implicated in diabetic neuropathy and may serve as new therapeutic targets.

SUMMARY

The best efforts of countless investigators have yet to find effective treatments either to stop the progression of axonal degeneration and cell death or regrow damaged axons. Basic research into the prevention of oxidative stress caused by excess glucose as well as the prevention of advanced glycation endproduct/receptor for advanced glycation endproduct signaling may offer new therapeutic targets. The use of skin biopsies may aid in early detection of both sensory and autonomic neuropathy, and perhaps in the case of patients with type 2 diabetes, diagnose neuropathy prior to the onset of symptoms.

Pseudoclaudication as a manifestation of diabetic neuropathy

We present the case of a 64-year-old male Type 1 diabetic patient with painful diabetic neuropathy masquerading as intermittent claudication. Examination of the peripheral circulation (both arterial and venous) was normal. An MRI scan excluded lumbar spinal stenosis and nerve root compression as the cause of claudication. The case suggests that, in the absence of other identifiable causes and in the presence of peripheral diabetic neuropathy, "intermittent claudication" may be due to the neuropathy itself.

The diabetic foot: update on a common clinical syndrome

A cross-sectional study was conducted in 3995 non-hospitalized diabetic patients to evaluate symptoms commonly associated with "diabetic foot" syndrome. Each patient was examined twice over 2 years during routine follow-up. The male/female ratio differed significantly between the study group and general population. Men were more prevalent in the diabetic group up to age 49 years. Thereafter, the proportion of females increased. The clinical signs present in various combinations in those with diabetic feet were dermatological findings, foot and toe deformities, open wounds and ulcerations, pulselessness, and neurological deficiencies. The female/male ratio for each symptom was significantly higher for women except for ulcerations, which were more common in men.

Tissue oxygenation and skin blood flow in the diabetic foot: responses to cutaneous warming

We previously reported an unexpected statistically significant decline in the mean transcutaneous partial pressure of oxygen (TcPO2) with cutaneous warming from 37 degrees C to 44 degrees C on the plantar diabetic foot, as opposed to the expected increase seen at the dorsal sites. To elucidate this relationship we compared changes with cutaneous warming in TcPO2 and skin circulation measured by laser Doppler flowmetry on the right plantar foot surface of 20 consecutive subjects. Neuropathy by monofilament testing was present in 55% of the cases. Right dorsal foot TcPO2 increased with cutaneous warming from 37 degrees C to 44 degrees by a mean change of +43.6+/-20.7 mmHg (+/- standard deviation) in 95% of the cases. In 42% of cases right plantar first metatarsal head TcPO2 fell with warming from 37 degrees C to 44 degrees C by a mean change of -10.7+/-7.6 mmHg. In the remaining 58% of cases right plantar first metatarsal head TcPO2 rose by 6.8+/-6.3 mmHg. In 95% of cases right plantar great toe laser Doppler perfusion units (LDPU) increased with warming from 36 degrees C to 44 degrees C by a mean change of +50.4+/-37.1. Blood flow measured by laser Doppler flowmetry increased in 95% of the subjects with heating. The finding that blood flow was increased with warming contradicts the hypothesis that arterioles in the plantar great toe cannot vasodilate in response to thermal stimuli. This finding supports the hypothesis that the decline in TcPO2 with warming might be due to an increase in epidermal oxygen consumption that exceeds the increase in oxygen delivery due to increased blood flow. The pathological mechanisms behind microvascular dysfunction in skin microcirculation in the diabetic foot need further investigation.

Posturally induced leg vasoconstrictive responses: relationship to standing duration, impedance and volume changes

Shifting legs to a gravity-dependent position provokes a physiological vasoconstrictive response that forms the basis of several diagnostic tests based on initial (< 5 min) blood perfusion decreases. However, it is not known if responses are maintained over longer duration and if they depend on the volume shifted to the limb during the manoeuvre. These issues were investigated by measurements of blood perfusion changes on foot and ankle (laser Doppler) and below-knee volume and impedance changes induced by 30 min of standing in 10 healthy volunteers. Initial perfusion decreases were 66.4% +/- 2.6% and 49.3% +/- 3.8% for ankle and foot dorsum, respectively, and were fully maintained during sustained standing without evidence of 'vasodilator escape'. Response magnitudes were not dependent on leg volume changes using geometric or impedance measures. A close correlation (r2 = 0.78) between impedance and volume changes suggests the former as a useful way of assessing dynamic limb volume changes. Sustained vasoconstrictive responses make it unlikely that extending the duration of such tests would offer more, diagnostic information than is currently available.

Normal blood flow response and vasomotion in the diabetic Charcot foot

Vasomotion, the spontaneous rhythmic contraction exhibited by small arteries and arterioles is dysregulated in patients with diabetic neuropathy. We examined the relationship between Charcot arthropathy and vasomotion at the dorsum of the foot. We studied nine diabetic patients with clinically diagnosed neuropathy and Charcot arthropathy in 13 feet (n=13), twelve subjects with diabetic neuropathy and no Charcot deformity (n=12), and 11 healthy controls (n=11). Following neuropathy assessment, blood flow was measured by laser Doppler flowmetry with local skin warming. Fast Fourier transformation was performed to provide an index of vasomotion. Subjects with Charcot osteoarthropathy had more severe somatic neuropathy and higher circulating levels of serum calcium (9.8+/-0.1 versus 9.3+/-0.1 mg/dL). Raising local temperature increased skin blood flow and vasomotion in both control subjects and Charcot subjects, but not in diabetic patients with neuropathy alone (p < 0.05 for blood flow, p < 0.02 for vasomotion). Patterns of peripheral vasomotion and blood flow which are clearly disordered in diabetic neuropathy are intact in patients with a Charcot osteoarthropathy, despite a more severe sensory nerve impairment. These findings suggest that the loss of peripheral blood flow and vasomotion often seen in diabetic neuropathy may actually be protective against Charcot arthropathy by preventing bone resorption. It remains unclear then whether the Charcot arthropathy is a direct result of a failure to decrease blood flow to bone, or is the manifestation of some other pathology.

Development of vascular complications in diabetes

Chronic complications of diabetes are dominated by disorders of the vascular system. They are a much larger burden on both diabetic patients and overall medical costs than diabetes itself. Large vessel problems are far more frequent than microvascular disorders. Loss of arterial elasticity alters arterial flow patterns and increases microcirculatory peak flow rates. Hyperglycemia may directly disrupt elastin formation. Diabetic leg artery disease may be generated by nerve damage, reversing this interactive contribution sequence. The major anatomic feature of microangiopathy in long-term diabetes is an unevenly distributed thickening of the intima of smaller arterioles. The thickening is primarily due to accumulation of type IV (basement membrane) collagen. Arterioles change local vessel diameter to adjust blood distribution to meet current needs. The thickening compromises the maximum local blood flow that may be achieved by this means. Compromise of maximal arteriolar dilatation does not disrupt exercising muscle but in the kidney, retina, and possibly in nerve, local circumstances can generate serious damage. Each of these system's responses has unique features that mediate its vulnerability, but all these organs show arteriolar hyalinization. The increased arteriolar accumulation of type IV collagen appears to be a response to the tangential force generated by flow over local endothelial cells. An increase in peak arteriolar wall force is mediated by a diabetes-specific doubling of erythrocyte membrane curvature change resistance. Red cell aggregation rate determines the rate of damage. The same nonspecific burden may also predispose to heart disease and stroke. Intensive metabolic control improves red cell deformability and protects against arteriolar damage. Therapies that address the rheologic problem more directly may add to the effectiveness of good diabetes control in the future.

Comparative assessment of peripheral sympathetic function by postural vasoconstriction arteriolar reflex and sympathetic skin response in NIDDM patients

PURPOSE

The aim of the study was to compare peripheral sympathetic adrenergic and cholinergic nerve function in NIDDM (non-insulin-dependent diabetes mellitus) patients with various degrees of diabetic neuropathy and neuropathic foot ulceration. The parameters used were postural vasoconstriction arteriolar reflex (VAR) and sympathetic skin response (SSR), respectively.

PATIENTS AND METHODS

Forty-seven NIDDM patients were studied. No patients had clinically significant peripheral vascular disease. They were divided according to peripheral somatic neuropathy, assessed by clinical score and vibration perception threshold (VPT). Twenty-two patients showed no significant evidence of peripheral neuropathy and normal VPT (DN-); 15 had signs and symptoms of neuropathy and VPT alteration (DN+); 10 had diabetic neuropathy and foot ulceration (DNU). Twenty-two normal subjects were also examined as a control group. Resting arteriovenous shunt skin blood flow, measured using laser-Doppler flowmetry, and the VAR of the big toe on lowering the foot were studied. Sympathetic skin response was assessed by an EMG apparatus. Autonomic function was also investigated by using standard cardiovascular reflex tests.

RESULTS

Resting blood flow values were similar in the three NIDDM groups and in the control group. VAR to foot lowering was significantly impaired in all NIDDM groups by comparison with controls (72.8 +/- 2.1%, mean +/- SEM), this impairment being progressively more pronounced in DN- (58.8 +/- 2.3%, P < 0.001), DN+ (33.3 +/- 3.0%, P < 0.001 versus DN-) and DNU (8.6 +/- 2.7%, P < 0.001 versus DN+). Sympathetic skin response was assessed in 28 patients and was significantly impaired in DN-compared with the control group (2.53 +/- 0.04 versus 2.71 +/- 0.04 log mcV, P < 0.01). This impairment was severe in the DNU compared with the DN+ group (1.36 +/- 0.05 versus 2.26 +/- 0.04 log mcV, P < 0.005). A positive correlation was found between VAR values and SSR (P < 0.001), and these measurements were also closely correlated with several parameters of central autonomic and somatic neuropathy.

CONCLUSION

These results indicate that peripheral sympathetic adrenergic and cholinergic fibers simultaneously undergo early alterations in diabetic patients, even when there is no clinical neuropathy. Our data also show almost complete abolition of peripheral sympathetic activity in NIDDM patients with foot ulceration.

Assessment of ischaemic feet in diabetes

Transcutaneous oximetry, laser Doppler flowmetry and ankle brachial systolic pressure indices were used to investigate blood flow to the feet in 26 subjects with diabetes mellitus and peripheral arterial disease. A total of 21 critically ischaemic feet and 15 non-critically ischaemic feet were investigated. Using laser Doppler flowmetry, non-critically ischaemic feet demonstrated a significant increase in maximum blood flow, and percentage increase in flow following local heating (p = 0.038, p = 0.012) in comparison with critically ischaemic feet. These statistically significant differences reflect an increased hyperaemic response in non-critically ischaemic feet.

A disturbed macrocirculatory supply as a determinant for a reduced sciatic nerve blood flow in diabetic rats

The aim of this study was to evaluate macrocirculatory disturbances in relation to the reduced sciatic nerve blood flow seen in diabetic rats. Therefore, both femoral blood flow, the macrocirculatory arterial blood supply to the sciatic nerve, and the microcirculatory neuronal blood flow were measured. In order to differentiate between a direct vascular or a neuronal defect as a cause for the disturbed macrocirculatory blood flow the effects of the adrenocorticotropic hormone [ACTH]-(4-9) analogue, Org 2766, a neurotrophic compound without cardiovascular effects, were investigated on the femoral flow under basal as well as adrenergic-stimulated conditions. Adrenergic responsiveness to tyramine and phenylephrine effect on femoral flow was determined. Basal sciatic nerve and femoral blood flow were reduced by 48% and 42%, respectively, after 12 weeks of diabetes, without effect on blood pressure. Treatment with Org 2766, beginning 6 weeks after the induction of diabetes, had no influence on these basal haemodynamic variables. Femoral flow in diabetic rats showed a smaller response to tyramine and phenylephrine compared to the control. Org 2766 restored this disturbed flow response to that of the control rats. In conclusion, the decrease in basal femoral flow might be responsible for the lowered sciatic nerve blood flow. Although neuronal disturbances due to diabetes had a very minor role in the reduction of basal femoral blood flow the adrenergic-stimulated flow responsiveness was seriously affected in diabetic rats.

Superficial Heat and Cold

In brief The wide array of superficial heat and cold modalities offers physicians many options for treating sports-related injuries. Appropriate application of heat and cold therapies can reduce the impact of an injury by relieving pain, reducing swelling, and encouraging rehabilitation.

Abnormal digital pressure measurements in diabetic neuropathic foot ulceration

The diabetic neuropathic ulcer is typically slow to heal and recurrent. Macrovascular insufficiency is usually excluded as foot pulses are present and ankle:brachial pressure ratios are not decreased. These assessments cannot however exclude more distal vascular disease. Digital pressure measurements enable a reliable assessment of the distal peripheral vascular status to be made. The aim of this study was therefore to use toe pressures to assess the contribution of distal ischaemia in the pathogenesis of the neuropathic ulcer. Sixteen diabetic patients with recurrent neuropathic foot ulceration had their toe pressures compared to 10 neuropathic patients without a history of foot ulceration, 10 diabetic control subjects, and 11 normal subjects. Four non-diabetic patients with neuropathy and foot ulceration were also assessed. All subjects had ankle:brachial pressure indices > or = 1. Toe pressure was assessed using laser Doppler flowmetry to record the return of skin blood flow. The toe:brachial pressure index (TBI) was then calculated. The diabetic patients with a history of recurrent neuropathic ulceration, had the lowest mean TBI, 0.63 +/- 0.14 (SD), compared to the non-ulcerated diabetic neuropathy patients, the diabetic control subjects, and the normal subjects. 0.84 +/- 0.11, 0.82 +/- 0.1, and 0.81 +/- 0.07, p < 0.01, respectively. Three of the four non-diabetic patients with neuropathic foot ulceration also had an abnormally low TBI. Reduced toe pressure measurements are thus found to be associated with neuropathic foot ulceration. The contribution of distal ischaemia in the pathogenesis of the diabetic neuropathic foot ulcer needs to be evaluated.

Selective neuropathy and preserved vascular responses in the diabetic Charcot foot

Charcot arthropathy is a disabling complication of diabetic neuropathy. It is however, unclear why it occurs in only a small number of neuropathic patients. We have studied 12 diabetic patients (10 insulin-dependent) with an acute Charcot arthropathy, and compared their neuropathy and vascular responsiveness with 12 diabetic patients (10 insulin-dependent) with recurrent neuropathic foot ulceration, 12 diabetic control subjects (9 insulin-dependent) and 10 normal non-diabetic subjects. The Charcot arthropathy patients demonstrated a preservation of warm perception, 6 (5.5) degrees C, but complete loss of peripheral cold perception, 10 (0) degrees C, p less than 0.001 (median (interquartile range)). This contrasted with the ulcerated neuropathy patients, who had equally severe impairement of both warm and cold sensory thresholds, 10(0.5) degrees C vs 10(1) degrees C, respectively, the diabetic control subjects who were able to detect a 2 (1.3) degrees C warm stimulus and 3 (3.5) degrees C cold stimulus and the normal subjects, whose warm threshold was 2 (1) degrees C and cold was 2 (1) degrees C. Light touch perception at the foot was preserved in the Charcot patients 4 (4) g vs 100 (50) g, p less than 0.0002, in the ulcerated neuropathy patients. Vibration perception at the great toe and cardiovascular autonomic function tests (heart rate variability, Valsalva ratio and postural systolic blood pressure fall) were abnormal in both the Charcot patients and ulcerated neuropathy group, with no differences seen between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Paradoxical blood flow responses in the diabetic neuropathic foot: an assessment of the contribution of vascular denervation and microangiopathy

Blood flow is abnormal in the diabetic neuropathic foot, and this may be of importance in the pathogenesis of complications. Arteriovenous shunting is increased, and blood flow through these channels may paradoxically decrease in response to local heating. Peak skin blood flow is also reduced in these patients. It is not known whether these blood flow abnormalities may reflect diabetic microangiopathy, or whether they simply reflect vascular denervation. The skin blood flow response to a local thermal stimulus was studied in four non-diabetic patients with a unilateral traumatic neuropathy and foot ulceration. All showed a decrease in skin blood flow (to 68% of basal) at the great toe during local heating in the neuropathic limb, in contrast to the normal limb, in which blood flow increased to 180% of basal. Peak skin blood flow was also greatly reduced in the neuropathic limb, being only 29% of the normal limb. Neuropathy alone can be responsible for abnormal skin blood flow responses in the neuropathic foot.

Clinical observations and experiments in diabetic neuropathy

Diabetic neuropathies form a group of diverse conditions, which can be distinguished between those which recover (acute painful neuropathies, radiculopathies, mononeuropathies) and those which progress (sensory and autonomic neuropathies). These two main groups can be distinguished in several ways: sensory and autonomic neuropathies are classic diabetic complications progressing gradually in patients with long-standing diabetes who often have other specific complications, while the reversible neuropathies do not have these features. The latter are characterised by their occurrence at any stage of diabetes, often at diagnosis, they may be precipitated on starting insulin treatment, and they are more common in men; they can occur at any age, though more often in older patients, and are unrelated to other diabetic complications. The two groups of neuropathies also show differences in nerve structural abnormalities and with regard to distinctive blood flow responses. The underlying mechanisms responsible for these very different forms of neuropathy remain speculative, but evidence for an immunological basis for the development of severe symptomatic autonomic neuropathy is presented.

Diabetic autonomic neuropathy

One of the earliest manifestations of diabetic neuropathy is denervation of the cardiovascular system; loss of heart rate variability may have a prevalence as high as 21.5% in diabetic patients, and declines at 1 beat/min/year, which is 3 times faster than in normal subjects. The cause of this neuropathy is unknown: attempts at decreasing the excess quantities of sorbitol, glucose and fructose in nerve tissue have lead to little functional improvement in man. Nerve ischaemia and immunological damage have stimulated increased interest lately, the latter particularly because of the structural homology of nerve growth factor and insulin. Symptoms from autonomic neuropathy are rare. When present they may well be intermittent, but never remit; they rarely progress or become disabling. One uncommon consequente of loss of sympathetic vascular tone is postural hypotension. This may result from failure of splanchnic vasoconstriction on standing. Food and insulin can greatly exacerbate the postural blood pressure fall. Reduced vascular tone in the neuropathic foot leads to increased arterio-venous shunt flow. The local reflex control of this shunt flow is also abnormal: paradoxical vasoconstriction occurs in response to local skin heating and postural reflexes are reduced. This high shunt flow together with its abnormal vascular control may be important in the pathogenesis of neuroarthropathy and foot ulceration. The prognosis of patients with autonomic neuropathy is better than previously reported. Abnormal heart rate variability alone is of no prognostic value. The presence of symptoms, in particular postural hypotension, significantly reduces survival. The majority of deaths however, result from concurrent renal disease and macrovessel atheroma.