Pathophysiology and treatment of painful diabetic neuropathy of the lower extremity

BACKGROUND

Symptomatic peripheral neuropathy is the most common complication of diabetes mellitus, affecting up to 62% of Americans with diabetes.

METHODS

We reviewed the literature using the National Library of Medicine's MEDLINE search service. In total, we reviewed 54 articles.

RESULTS

Hyperglycemia leads to increased activity in the polyol pathway in nerve cells; this ultimately results in abnormal nerve function. Numerous pharmacologic agents have been used to treat symptomatic peripheral neuropathy, but all of these drugs can be associated with adverse side effects. Recent work has indicated that subsensory electrical stimulation may be preferred to pharmacotherapy, since it is equally effective and has a more favorable safety profile.

CONCLUSION

Although the pathophysiology of diabetic neuropathy is well understood, treatment of the symptoms associated with this condition can be challenging. Additional research is needed to reveal a safe and effective treatment for this debilitating sequela of diabetes mellitus.

1998 William J. Stickel Silver Award. Mechanically assisted, delayed primary closure of diabetic foot wounds

The authors evaluated the time to healing and prevalence of complications in patients undergoing mechanically assisted, delayed primary closure of diabetic foot wounds compared with a similar population who received standard wound care. A total of 55 patients were enrolled for study, with 25 in the experimental group and 30 in the control group. Patients in the experimental (stretch) group underwent mechanically assisted primary closure of their wounds using a skin-stretching device. There was no difference between the stretch and control groups with regard to any descriptive characteristics, including wound chronicity. Although the wounds were over three times as large on average in the stretch group (P < .001), the stretch group reached full epithelialization approximately 40% sooner than the control group (26.4 +/- 16.0 versus 42.5 +/- 19.9 days; P < .002). Eighty-eight percent of patients in the stretch group experienced wound dehiscence, at a mean time of 1.8 +/- 0.6 weeks following mechanically assisted closure. However, patients who experienced dehiscence in the stretch group healed significantly faster than patients in the control group (27.4 +/- 16.7 versus 42.5 +/- 19.9 days; P < .007). The results of this study suggest that mechanically assisted closure of diabetic foot wounds may result in reduced healing time compared with healing by secondary intention.

The effect of increased weight on peak pressures: implications for obesity and diabetic foot pathology

The purpose of this study was to determine if increased weight contributes to increased mean peak plantar foot pressures when foot function, deformity, and structure are controlled. Ten male and nine female volunteers without sensory neuropathy or other systemic disease were evaluated in the study. Using a repeated measures design, peak plantar foot pressures were compared using the Novel Pedar in-shoe pressure measurement system under three conditions. Baseline measurements were made while volunteers wore the standard test footwear, a thin-soled rubber oxford sneaker. The second and third test conditions involved pressure measurements with an additional 9.1 kg (20 lb) and 18.2 kg (40 lb), respectively, of weight evenly distributed in pockets on the front and back of a workout vest. There was a significant increase in mean peak plantar foot pressures under the metatarsal heads, heel, and midfoot for each incremental increase of weight (baseline vs. 9.1 kg, p < .05; 9.1 kg vs. 18.2 kg, p < .05). The authors conclude that increases in weight increased plantar foot pressures for the first metatarsal, lesser metatarsal, midfoot, and heel regions in both men and women.

The benefit of electrical stimulation to enhance perfusion in persons with diabetes mellitus

The purpose of this study was to evaluate the effect of galvanic electrical stimulation on vascular perfusion in diabetic patients. Nineteen subjects with diabetes were enrolled. Eleven subjects (57.9%) were diagnosed with impaired peripheral perfusion based upon their initial transcutaneous oximetry values (< 40 mm Hg). The subjects were studied over a 2-day period. On the 1st day, one foot was electrically stimulated for four 60-minute periods by an external electrical stimulation device. Vascular perfusion of both feet was assessed before and after the sessions of electrical stimulation. On the 2nd day, no electrical stimulation was applied and noninvasive vascular measurements were repeated. For the 1st hour, transcutaneous oxygen pressure was measured continuously during stimulation at the lateral aspect of the leg. Subsequently, perfusion between the periods of stimulation was measured on the dorsum of the foot with both transcutaneous oximetry and laser Doppler flowmetry after each stimulation period. In the group with impaired peripheral perfusion, a significant rise in tissue oxygenation as compared to the control measurements was measured during the first 5 minutes of stimulation (p < .040). For those without vascular disease (TcpO2 > 40 mm Hg) however, there was not a significant increase compared to baseline (p = .280). After the periods of stimulation, the stimulated feet did not show any higher perfusion levels than the control feet. Patterns in perfusion during the day, as measured by laser Doppler flowmetry, were similar in the tested feet and in the controls. These data suggest that external subsensory electrical stimulation induces a transient rise in skin perfusion in persons with diabetes and impaired peripheral perfusion.

Is Charcot arthropathy a late sequela of osteoporosis in patients with diabetes mellitus?

It is well accepted that Charcot arthropathy is most frequently encountered in the diabetic population. Also well known is the association between diabetes and osteoporosis, even in the absence of overt renal dysfunction. Is it plausible that Charcot arthropathy is a late sequela of osteoporosis in diabetic patients, and if so, can the osteoporosis be treated early, leading to a decrease in the ultimate prevalence of Charcot arthropathy? The objective of this paper is to concisely review the literature detailing the course of Charcot neuroarthropathy and to investigate the links between Charcot arthropathy and osteoporosis among diabetic patients.

Risk factors for above-knee amputations in diabetes mellitus

BACKGROUND

Above-knee amputation (AKA) is a common complication in diabetics, mostly after one or more lower level amputations (LEAs) have been done. The aim of this study was to identify risk factors for AKAs among diabetics.

METHODS

We abstracted 1,800 medical records of hospitalizations for LEA. Kaplan's comorbidity classification was used to rank disease severity. We used both univariate and multivariate models to identify risk factors for AKA.

RESULTS

Of the 1,043 diabetic amputees in this study, 22% had AKA. Variables associated with AKA were locomotor impairment, severe anemia, history of lower extremity bypass surgery, body mass index (BMI) < 20 kg/m2, female sex, cerebrovascular disease, cardiovascular disease, and SGOT > 40 U/L.

CONCLUSIONS

Most of these risk factors represent end-stage processes and do not have good treatment alternatives. Perhaps one of the practical applications of these data is not to describe risk of proximal amputations but instead to look more closely at candidates who should be considered for distal procedures.

Is there a critical level of plantar foot pressure to identify patients at risk for neuropathic foot ulceration?

The purpose of this study was to identify a point along the spectrum of peak plantar forefoot pressure that has an optimum combination of sensitivity and specificity to screen for neuropathic ulceration. We enrolled 219 diabetic patients in this case-control study in an approximate 2:1 control:case ratio. Cases were defined as patients with an active or recently healed neuropathic ulceration. Controls were defined as those with no history of ulceration. All patients had peak plantar pressures analyzed with the EMED gait analysis system. Peak plantar pressure was, as expected, significantly higher for patients with ulcers compared to controls [83.1 +/- 24.7 N/cm2 (range, 10-125) vs. 62.7 +/- 24.4 N/cm2 (range, 7.3-113), p < .001]. The ulcer group was clearly skewed toward a higher prevalence of elevated peak plantar forefoot pressure compared with the control group, which displayed the opposite trend (control group skewness = 0.286, kurtosis = -0.482; ulcer group skewness = -0.389, kurtosis = -0.289). Using receiver operating characteristic analysis, the optimal cut-point, as determined by a balance of sensitivity and specificity was 70 N/cm2, which yielded a sensitivity of 70.0% and a specificity of 65.1%. We concluded that, while there is no optimal cut-point for clearly screening patients for risk of foot ulceration, the higher the peak pressure, the higher the commensurate risk.

Emergence of non-group A streptococcal necrotizing diabetic foot infections

Recently the authors have noted a disturbing trend toward an increased incidence of necrotizing infections caused by non-group A streptococcal species. This article describes the typical clinical course of such an infection. Prompt surgical intervention, coupled with an antibiotic regimen aimed at mitigating exotoxin release, may be both limb- and life-preserving.

Cost of diabetes-related amputations in minorities

The objective of this study was to identify the direct cost and length of hospitalization of diabetes-related lower extremity amputations among Hispanics, African Americans, non-Hispanic whites, and Asians. The authors used a database from the office of Statewide Planning and Development in California that identified all hospitalizations for lower extremity amputations in the state in 1991. Amputation level was defined by the ICD-9-CM codes 84.11-84.18. The total hospital charges for diabetes-related lower extremity amputations for the state of California in 1991 was $141 million. The mean hospital charge (HC) per patient with all ethnic groups combined was $27,930; and the mean length of stay (LOS) was 15.9 days. African Americans had significantly higher mean charges ($32,383) and longer stays (17.3 days) compared to all other ethnic groups (p < .05). Toe-level amputations had lower HC (p < .05) and LOS (p < .01) than other amputation levels for all race groups. One-quarter of the population received multiple amputations during their hospital stay. These patients incurred significantly higher hospital charges ($44,731) and stayed in the hospital longer (23.4 days) than those receiving only a single amputation. There was a considerable variation in the HC and LOS among ethnic groups by level of amputation. The direct charges reported in this study suggest considerably higher overall direct costs than have been previously reported in the medical literature. The greater burden of disease experienced by African Americans is probably related to their higher amputation cost and longer hospitalization.

Vibration perception threshold: are multiple sites of testing superior to single site testing on diabetic foot examination?

Vibration perception threshold (VPT) values, measured at different anatomic locations on the foot and ankle, and the time to assess VPT and sensory perception using two difference modalities in 102 diabetic patients were compared. VPT was evaluated at the great toe, fifth metatarsal and ankle. Differences in VPT at these three sites, in addition to differences in duration of testing comparing single site (great toe) to multiple sites, and to standard SWMF testing were assessed. No significant difference in VPT between the great toe and fifth metatarsal was found for patients both with and without loss of protective sensation (LOPS). Mean VPT was significantly higher at the ankle compared with both the great toes and fifth metatarsals. However, the difference between ankle and great toe was not significant between patients with and without LOPS [3.9 +/- 11.2 (12%) vs. 3.0 +/- 10.8 (16%) volts, respectively, p > 0.6]. Testing of one site took approximately half the time of Semmes-Weinstein 10-gram monofilament wire SWMF testing (40.5 +/- 16.9 vs. 22.3 +/- 9.1 seconds, p < 0.01) and less than one third the time of three-site VPT testing (10.5 +/- 26.1 vs. 22.3 +/- 9.1 seconds, p < 0.01). There may not be a significant practical benefit in multiple site VPT testing when compared with single site testing on the great toe alone. The value of multiple site testing is further called into question when one notes that the great toe VPT remains the only site tested for sensitivity and specificity for ulceration.

Validation of a diabetic wound classification system. The contribution of depth, infection, and ischemia to risk of amputation

OBJECTIVE

To validate a wound classification instrument that includes assessment of depth, infection, and ischemia based on the eventual outcome of the wound.

RESEARCH DESIGN AND METHODS

We evaluated the medical records of 360 diabetic patients presenting for care of foot wounds at a multidisciplinary tertiary care foot clinic. As per protocol, all patients had a standardized evaluation to assess wound depth, sensory neuropathy, vascular insufficiency, and infection. Patients were assessed at 6 months after their initial evaluation to see whether an amputation had been performed.

RESULTS

There was a significant overall trend toward increased prevalence of amputations as wounds increased in both depth (chi 2trend = 143.1, P < 0.001) and stage (chi 2trend = 91.0, P < 0.001). This was true for every subcategory as well with the exception of noninfected, nonischemic ulcers. There were no amputations performed within this stage during the follow-up period. Patients were more than 11 times more likely to receive a midfoot or higher level amputation if their wound probed to bone (18.3 vs. 2.0%, P < 0.001, chi 2 = 31.5, odds ratio (OR) = 11.1, CI = 4.0-30.3). Patients with infection and ischemia were nearly 90 times more likely to receive a midfoot or higher amputation compared with patients in less advanced wound stages (76.5 vs. 3.5%, P < 0.001, chi 2 = 133.5, OR = 89.6, CI = 25-316).

CONCLUSIONS

Outcomes deteriorated with increasing grade and stage of wounds when measured using the University of Texas Wound Classification System.

Risk factors for diabetic foot ulceration: a logical approach to treatment

Appropriate management of the diabetic foot in a multidisciplinary setting requires knowledge of the risk factors leading to ulceration and limb loss. This article will review the most common risk factors for ulceration and present a validated, treatment-based method to appropriately communicate both the status of the diabetic wound and, more important, the patient's location on a spectrum of risk for amputation.

Defining loss of protective sensation in the diabetic foot

Although the importance of distal symmetric sensorimotor polyneuropathy as a risk factor for diabetic foot ulceration has been known for decades, attempts to identify the elusive point that defines loss of protective sensation have been futile. This manuscript will review the epidemiology and pathogenesis of peripheral neuropathy, discuss commonly used screening tools, and review recently reported data that more sharply define loss of protective sensation on the long spectrum of neuropathy.

Insulin-like growth factor binding protein -2 and -4 messenger ribonucleic acid expression in bovine ovarian follicles: effect of gonadotropins and developmental status

This work is concerned with the role of insulin-like growth factor binding protein (IGFBP)-2 and -4 in the regulation of IGF bioactivity in bovine follicles during the development of dominance. We measured the expression of IGFBP-2 and -4 messenger RNA (mRNA) in small (1-4 mm) gonadotropin-sensitive follicles and medium (4-8 mm) and large (>8 mm) gonadotropin-dependent follicles using in situ hybridization. In healthy nonatretic bovine follicles, IGFBP-2 and -4 mRNA expression was confined to granulosa and theca tissue, respectively. Moreover, during the development of follicular atresia, there were distinct changes in the temporal and spatial expression of these genes. IGFBP-2 immunoactivity was localized in granulosa tissue and the basement membrane of healthy preantral follicles, whereas IGFBP-4 immunoactivity was localized in both theca and granulosa tissue. Of particular interest was the lack of IGFBP-2 mRNA expression in large (>8 mm) gonadotropin-dependent follicles, an observation that was confirmed by the lack of immunoreactive IGFBP-2 in these follicles. The regulation of IGFBP-2 and -4 mRNA expression in granulosa and theca cells was analyzed using a serum-free cell culture system. FSH inhibited the expression of IGFBP-2 mRNA in granulosa cells, whereas LH stimulated IGFBP-4 mRNA expression in theca cells. Our results provide evidence for the existence of different roles for IGFBP-2 and -4 in the developing follicle.

Diabetic foot ulcers: prevention, diagnosis and classification

Diabetic ulcers are the most common foot injuries leading to lower extremity amputation. Family physicians have a pivotal role in the prevention or early diagnosis of diabetic foot complications. Management of the diabetic foot requires a thorough knowledge of the major risk factors for amputation, frequent routine evaluation and meticulous preventive maintenance. The most common risk factors for ulcer formation include diabetic neuropathy, structural foot deformity and peripheral arterial occlusive disease. A careful physical examination, buttressed by monofilament testing for neuropathy and noninvasive testing for arterial insufficiency, can identify patients at risk for foot ulcers and appropriately classify patients who already have ulcers or other diabetic foot complications. Patient education regarding foot hygiene, nail care and proper footwear is crucial to reducing the risk of an injury that can lead to ulcer formation. Adherence to a systematic regimen of diagnosis and classification can improve communication between family physicians and diabetes subspecialists and facilitate appropriate treatment of complications. This team approach may ultimately lead to a reduction in lower extremity amputations related to diabetes.

Elevated peak plantar pressures in patients who have Charcot arthropathy

Although diabetes and peripheral neuropathy are perhaps the most important risk factors for neuropathic osteoarthropathy, we hypothesized that peak plantar pressures may also be higher in patients who have this condition. We are unaware of any reports in the medical literature that have specifically addressed this hypothesis. We obtained data from the medical records of 164 diabetic patients who had been managed in a multidisciplinary tertiary-care diabetic foot-specialty clinic. We then divided the patients into four groups: those who had acute Charcot arthropathy, those who had neuropathic ulceration, those who had neuropathy without ulceration, and those who had neither neuropathy nor ulceration. The peak plantar pressures were significantly higher in the patients who had acute Charcot arthropathy and those who had a neuropathic ulcer (p < 0.001 for both) compared with the pressures in those who had no history of arthropathy and those who had neuropathy without ulceration. With the numbers available, we could not detect a significant difference in the peak pressure between the affected and the unaffected foot in the patients who had Charcot arthropathy (mean [and standard deviation], 100+/-8.5 compared with 101+/-9.6 newtons per square centimeter; p > 0.05). However, the mean peak pressure was significantly higher on the ulcerated side than on the contralateral side in the patients who had a neuropathic ulcer (90+/-18.8 compared with 86+/-20.7 newtons per square centimeter; p < 0.02). Although the midfoot was the site of maximum involvement in all patients who had Charcot arthropathy, the peak plantar pressure was on the forefoot, suggesting that the forefoot may function as a lever, forcing collapse in the midfoot.

Plantar pressures are higher in diabetic patients following partial foot amputation

The purpose of this study was to compare peak plantar pressure in diabetic patients with and without foot-level amputation. This project was conducted as a case-control study. We enrolled 27 cases and 150 controls diagnosed with diabetes mellitus. Cases were defined as patients with a history of forefoot-level amputation (digit or ray amputations distal to the tarsometatarsal joint) secondary to an infected forefoot wound. Controls were defined as subjects that had never had a foot ulceration. We used a pressure platform system to evaluate dynamic barefoot pressure on the sole of the foot. There was no significant difference in vascular perfusion or body mass index between the case and control groups. Patients with a foot-level amputation were nearly ten times more likely to present with limited joint mobility or a rigid foot deformity than those without amputation (92.6% vs. 44.0%, p < 0.0001, X2 = 13.0, Odds Ratio = 9.8 CI = 2.2 to 43.0). Peak plantar pressure was significantly higher for patients with amputations compared to controls (80.0 +/- 31.1 N/cm2, vs, 62.5 +/- 21.0 N/cm2, p < 0.001). Peak pressure and limited joint mobility have long been associated with ulceration. We conclude that increased pressure and contractures associated with biomechanical compensation following a partial foot amputation further increase plantar pressure, placing an already high-risk limb at further risk for tissue breakdown and reamputation.

Choosing a practical screening instrument to identify patients at risk for diabetic foot ulceration

OBJECTIVE

To evaluate the sensitivity and specificity of 3 sensory perception testing instruments to screen for risk of diabetic foot ulceration.

METHODS

This case-control study prospectively measured the degree of peripheral sensory neuropathy in diabetic patients with and without foot ulcers. We enrolled 115 age-matched diabetic patients (40% male) with a case-control ratio of approximately 1:3 (30 cases and 85 controls) from a tertiary care diabetic foot specialty clinic. Cases were defined as individuals who had an existing foot ulceration or a history of a recently (< 4 weeks) healed foot ulceration. Controls were defined as subjects with no foot ulceration history. Using receiver operating characteristic analysis, we evaluated the sensitivity and specificity of 2 commonly used nephropathy assessment tools (vibration perception threshold testing and the Semmes-Weinstein 10-g monofilament wire system) and a 4-question verbal neuropathy score to evaluate for presence of foot ulceration.

RESULTS

A vibration perception threshold testing using 25 V and lack of perception at 4 or more sites using the Semmes-Weinstein 10-g monofilament wire system had a significantly higher specificity than neuropathy score used. The neuropathy score was most sensitive when 1 or more answers were affirmative. When modalities were combined, particularly the monofilament wire system plus vibration perception threshold testing and the neuropathy score plus the monofilament wire system, there was a substantial increase in specificity with little or no diminution in sensitivity.

CONCLUSIONS

The early detection of peripheral neuropathy or loss of "protective sensation" is paramount to instituting a structured treatment plan to prevent lower extremity amputation. The results of our study suggest that all 3 sensory perception testing instruments are sensitive in identifying patients at risk for ulceration. Combining modalities appears to increase specificity with very little or no diminution in sensitivity.

Practical criteria for screening patients at high risk for diabetic foot ulceration

BACKGROUND

A comprehensive understanding of clinical risk factors for developing foot ulcerations would help clinicians to categorize patients by their risk status and schedule intervention resources accordingly to prevent amputation.

OBJECTIVE

To evaluate risk factors for foot ulcerations among persons with diabetes mellitus.

METHOD

We enrolled 225 age-matched patients, 46.7% male, with a ratio of approximately 1:2 cases: controls (76 case-patients and 149 control subjects). Case-patients were defined as subjects who met the enrollment criteria and who had an existing foot ulceration or a recent history of a foot ulceration. Control subjects were defined as subjects with no history of foot ulceration. A stepwise logistic regression model was used for analysis.

RESULTS

An elevated plantar pressure (> 65 N/cm2), history of amputation, lengthy duration of diabetes (> 10 years), foot deformities (hallux rigidus or hammer toes), male sex, poor diabetes control (glycosylated hemoglobin > 9%), 1 or more subjective symptoms of neuropathy, and an elevated vibration perception threshold (> 25 V) were significantly associated with foot ulceration. In addition, 59 patients (78%) with ulceration had a rigid deformity directly associated with the site of ulceration. No significant associations were noted between vascular disease, level of formal education, nephropathy, retinopathy, impaired vision, or obesity and foot ulceration on multivariate analysis.

CONCLUSIONS

Neuropathy, foot deformity, high plantar pressures, and a history of amputation are significantly associated with the presence of foot ulceration. Although vascular and renal disease may result in delayed wound healing and subsequent amputation, they are not significant risk factors for the development of diabetic foot ulceration.

Reaching closure with skin stretching. Applications in the diabetic foot

At the present time, there are no evidence-based protocols outlining the use of the Sure-Closure Skin Stretching System on diabetic, neuropathic wounds. Ideally, surgical correction of the precipitating deformity and appropriate shoe gear accommodation should be performed con-comitantly with skin stretching (as indicated) to achieve an optimal long-term result. For several years, we have used the Sure-Closure device as an adjunctive treatment for diabetic-foot wound closure, and believe that, ultimately, this device more likely will be used in a clinical setting. In this manner, a patient with an open wound may, under aseptic conditions, be sequestered for a period of 1 to 2 hours during a clinical visit to allow for skin stretching. This procedure may be carried out two or three times weekly until closure is achieved. Mechanically assisted delayed primary closure is a relatively new category of wound closure; however, this device is by no means a panacea. Appropriate patient selection and intraoperative judgment are of critical preoperative and perioperative importance when employing this technique. Currently, we are completing a clinical trial comparing mechanically assisted delayed primary-wound closure to traditional treatment and off-loading in a population of high-risk diabetic patients. We believe that this project will better elucidate the relative indications and contraindications with what may be a very effective tool for the diabetic foot specialist.

Who is at risk for diabetic foot ulceration?

Diabetic foot ulceration is the most common cause of nontraumatic, lower-extremity amputation throughout the developed world. This article reviews recent data that report on various risk factors for ulceration. Subsequently, it discusses appropriate risk stratification for both the neuropathic ulcer specifically and the diabetic foot in general, using The University of Texas Diabetic Foot and Diabetic Wound Classification Systems. We believe that knowledge and communication of the most common risk factors precipitating ulceration and subsequent amputation lead to more consistent treatment of the diabetic foot, and, ultimately, to a reduction of its prevalence.

Evidence-based options for off-loading diabetic wounds

Whereas the treatment of the diabetic wound has received a great deal of attention in the medical literature, the majority of the focus of recent research has been centered on dressings and advanced wound healing modalities. All these methods, however, are less than effective if the central tenet of treating the diabetic wound, namely reducing plantar pressure through off-loading, is not addressed primarily. This article examines the most commonly used off-loading methods in the medical literature and discusses the attributes and disadvantages of many of these devices.

Is postural instability exacerbated by off-loading devices in high risk diabetics with foot ulcers?

Pressure reduction is of pivotal importance in any treatment plan designed to heal diabetic foot ulcers. However, to our knowledge, no work has evaluated the effect of ambulatory pressure reducing devices on postural stability (PS) in high risk diabetics. Therefore, the purpose of this study was to compare PS associated with 5 off-loading strategies: total contact casts with cast boot, total contact casts with heel, removable cast walker, half-shoes, and canvas shoes using a repeat measure design. Twenty-six diabetic patients with foot ulcers were enrolled in the study. Using a digital pressure platform, the degree of sway was measured as total deviation of center of force. Three 30 second trials were evaluated using Turkey's studentized range test for multiple comparisons (alpha = 0.05). Sway was significantly greater with total contact casts with heel compared to other devices. While total contact casting remains the gold standard with which to treat neuropathic ulcers, care should be taken when placing patients in any devices that may exacerbate postural instability. The results suggest that total contact casts with an incorporated rubber heel may indeed accentuate sway. It is therefore recommended that the rubber heel be eliminated in lieu of a protective cast boot when using this modality.