Thomas E. Lyons

Microvascular Reactivity and Inflammatory Cytokines in Painful and Painless Peripheral Diabetic Neuropathy

OBJECTIVE We investigated the association between inflammation, microvascular reactivity, and the development of peripheral diabetic neuropathy. RESEARCH DESIGN AND METHODS We studied three groups: 55 healthy control subjects, 80 nonneuropathic patients, and 77 neuropathic diabetic patients. We also subdivided the neuropathic patients into a subgroup of 31 subjects with painless neuropathy and 46 with painful neuropathy. We measured the foot skin endothelium-dependent and -independent vasodilation, the nerve axon reflex-related vasodilation (NARV), and inflammatory cytokines and biochemical markers of endothelial function. RESULTS The endothelium-dependent and -independent vasodilation and NARV were lower in the neuropathic group (P < 0.05). NARV was further reduced in the subgroup of painless neuropathy when compared to painful neuropathy (P < 0.05). Compared to the other two groups, the neuropathic group also had higher serum levels of PDGF AA/BB (P < 0.05), RANTES (P < 0.01), leptin (P < 0.0001), osteoprotegerin (P < 0.01), G-CSF (P < 0.05), sE-Selectin (P < 0.01), sICAM (P < 0.0001), sVCAM (P < 0.001), CRP (P < 0.0001), TNFalpha (P < 0.05), and fibrinogen (P < 0.05). Patients with painful neuropathy had higher sICAM-1 (P < 0.05) and CRP levels (P < 0.01) when compared to painless neuropathy. No major changes in the above results were observed in 78 diabetic patients who were seen for a second visit 21 months after the first visit. CONCLUSIONS Peripheral diabetic neuropathy is associated with increased biochemical markers of inflammation and endothelial dysfunction. Painful neuropathy is associated with further increase in inflammation and markers of endothelial dysfunction and preservation of the nerve axon reflex.

Early changes in the skin microcirculation and muscle metabolism of the diabetic foot.

BACKGROUND Changes in the large vessels and microcirculation of the diabetic foot are important in the development of foot ulceration and subsequent failure to heal existing ulcers. We investigated whether oxygen delivery and muscle metabolism of the lower extremity were factors in diabetic foot disease. METHODS We studied 108 patients (21 control individuals who did not have diabetes, 36 patients with diabetes who did not have neuropathy, and 51 patients with both diabetes and neuropathy). We used medical hyperspectral imaging (MHSI) to investigate the haemoglobin saturation (S(HSI)O2; % of oxyhaemoglobin in total haemoglobin [the sum of oxyhaemoglobin and deoxyhaemoglobin]) in the forearm and foot; we also used 31P-MRI scans to study the cellular metabolism of the foot muscles by measuring the concentrations of inorganic phosphate and phosphocreatine and calculating the ratio of inorganic phosphate to phosphocreatine (Pi/PCr). FINDINGS The forearm S(HSI)O2 during resting was different in all three groups, with the highest value in controls (mean 42 [SD 17]), followed by the non-neuropathic (32 [8]) and neuropathic (28 [8]) groups (p<0.0001). In the foot at resting, S(HSI)O2 was higher in the control (38 [22]) and non-neuropathic groups (37 [12]) than in the neuropathic group (30 [12]; p=0.027). The Pi/PCr ratio was higher in the non-neuropathic (0.41 [0.10]) and neuropathic groups (0.58 [0.26]) than in controls (0.20 [0.06]; p<0.0001). INTERPRETATION Our results indicate that tissue S(HSI)O2 is reduced in the skin of patients with diabetes, and that this impairment is accentuated in the presence of neuropathy in the diabetic foot. Additionally, energy reserves of the foot muscles are reduced in the presence of diabetes, suggesting that microcirculation could be a major reason for this difference.

Mechanisms Involved in the Development and Healing of Diabetic Foot Ulceration

We examined the role of vascular function and inflammation in the development and failure to heal diabetic foot ulcers (DFUs). We followed 104 diabetic patients for a period of 18.4 ± 10.8 months. At the beginning of the study, we evaluated vascular reactivity and serum inflammatory cytokines and growth factors. DFUs developed in 30 (29%) patients. DFU patients had more severe neuropathy, higher white blood cell count, and lower endothelium-dependent and -independent vasodilation in the macrocirculation. Complete ulcer healing was achieved in 16 (53%) patients, whereas 13 (47%) patients did not heal. There were no differences in the above parameters between the two groups, but patients whose ulcers failed to heal had higher tumor necrosis factor-α, monocyte chemoattractant protein-1, matrix metallopeptidase 9 (MMP-9), and fibroblast growth factor 2 serum levels when compared with those who healed. Skin biopsy analysis showed that compared with control subjects, diabetic patients had increased immune cell infiltration, expression of MMP-9, and protein tyrosine phosphatase-1B (PTP1B), which negatively regulates the signaling of insulin, leptin, and growth factors. We conclude that increased inflammation, expression of MMP-9, PTP1B, and aberrant growth factor levels are the main factors associated with failure to heal DFUs. Targeting these factors may prove helpful in the management of DFUs.

Differences in Joint Mobility and Foot Pressures Between Black and White Diabetic Patients

Limited joint mobility is common in diabetes and is related to high foot pressures and foot ulceration. We have examined the differences in joint mobility and foot pressures in four groups matched for age, sex, and duration of diabetes: 31 white diabetic, 33 white non‐diabetic, 24 black diabetic, and 22 non‐diabetic black subjects. Joint mobility was assessed using a goniometer at the fifth metacarpal, first metatarsal, and subtalar joints. In‐shoe and without shoes foot pressures were measured using an F‐Scan system. Neuropathy was evaluated using clinical symptoms (Neuropathy Symptom Score), signs (Neuropathy Disability Score), and Vibration Perception Threshold. There was no difference between white and black diabetic patients in Neuropathy Symptom Score, Neuropathy Disability Score, and Vibration Perception Threshold. Subtalar joint mobility was significantly reduced in white diabetic patients (22 ± 7°) compared to white controls (26 ± 4°, black diabetic patients (25 ± 5°), and black controls (29 ± 7°), and increased in black controls compared to white controls and black diabetic patients (level of statistical significance p < 0.05). Without shoes foot pressures were higher in white diabetic patients (8.31 ± 400 kg cm−2) compared to white controls (6.81 ± 2.31 kg cma2), black diabetic patients (6.2 ± 2.53 kg cm−2) and black controls (5.00 ± 1.24 kg cm−2) and lower in black controls compared to white and black diabetic patients (p < 0.05 in all cases). We conclude that racial differences exist in joint mobility and foot pressures between black and white subjects. Thus, in black diabetic patients the joint mobility, although reduced compared to black healthy subjects, is increased when compared to white diabetic patients. This contributes to lower foot pressures, comparable to non‐diabetic white subjects and probably reduces the risk of foot ulceration in black diabetic patients.

Role of Endothelial Progenitor Cells and Inflammatory Cytokines in Healing of Diabetic Foot Ulcers

Background To evaluate changes in endothelial progenitor cells (EPCs) and cytokines in patients with diabetic foot ulceration (DFU) in association with wound healing. Methods We studied healthy subjects, diabetic patients not at risk of DFU, at risk of DFU and with active DFU. We prospectively followed the DFU patients over a 12-week period. We also investigated similar changes in diabetic rabbit and mouse models of wound healing. Results All EPC phenotypes except the kinase insert domain receptor (KDR)+CD133+ were reduced in the at risk and the DFU groups compared to the controls. There were no major EPC differences between the control and not at risk group, and between the at risk and DFU groups. Serum stromal-cell derived factor-1 (SDF-1) and stem cell factor (SCF) were increased in DFU patients. DFU patients who healed their ulcers had lower CD34+KDR+ count at visits 3 and 4, serum c-reactive protein (CRP) and granulocyte-macrophage colony-stimulating factor (GM-CSF) at visit 1, interleukin-1 (IL-1) at visits 1 and 4. EPCs tended to be higher in both diabetic animal models when compared to their non-diabetic counterparts both before and ten days after wounding. Conclusions Uncomplicated diabetes does not affect EPCs. EPCs are reduced in patients at risk or with DFU while complete wound healing is associated with CD34+KDR+ reduction, suggesting possible increased homing. Low baseline CRP, IL-1α and GM-CSF serum levels were associated with complete wound healing and may potentially serve as prognostic markers of DFU healing. No animal model alone is representative of the human condition, indicating the need for multiple experimental models.

Diabetic Foot Complications: Diagnosis and Management

Foot complications in patients with diabetes mellitus are a challenge to the health care industry. A great deal of expenditure is due to the management of diabetic foot complications. This places a great burden on the health care industry. It also places a great burden on those diabetic patients with foot complications and their families. Therefore, their effective management in an efficient manner is crucial to our patients. To deal with these problems, a dedicated, knowledgeable, and experienced multidisciplinary team is key. Intervention at the earliest possible time yields the best outcome. Prevention is the focus for those with no ulcerations. For those with ulcerations, prompt recognition and treatment is key. The importance of classifying ulcerations according to size, depth, presence or absence of infection, and vascular status can not be overstated. Proper offloading is vital for those with neuropathic lesions. Recognition of patients with a component of ischemia and vascular intervention to increase perfusion will aid in wound healing. Of course deep infection requires immediate drainage. All efforts of those in the multidisciplinary team are directed at the restoration and maintenance of an ulcer-free foot which is important in enabling our patients to maintain their ambulatory status.

The evolving natural history of neurophysiologic function in patients with well-controlled diabetes.

This study aimed to investigate prospective changes to neurophysiologic function over 3 years in patients with well‐controlled diabetes. Sixty‐two subjects had neurologic examinations, symptom scores, autonomic testing, nerve conduction studies, quantitative sensory testing, and laser‐Doppler flowmetry at 18‐month intervals for 3 years. During the study, there was a 1 µV decrease in sural amplitude (p < 0.05), an increase in monofilament detection threshold of 0.36 g (p < 0.001), and a decrease in the axon‐reflex vasodilation in the foot (p < 0.005) and forearm (p < 0.05). There was an increase in symptoms of distal hypersensitivity (p < 0.005) but no change in neuropathy frequency or severity. Our findings suggest that laser‐Doppler flowmetry, a test of small fiber function, can detect the largest neurophysiologic change over time in groups of patients with diabetes. Sural nerve amplitude and monofilament thresholds may be more effective at detecting change in individual patients. Other tests of neurophysiologic function may require longer periods of time and greater numbers of participants to detect a difference. We conclude that patients with well‐controlled diabetes and optimal medical management of comorbid risk factors have low rates of neuropathy development and progression although the clinical relevance of this finding to the general population of individuals with diabetes is unknown.

Postexercise phosphocreatine recovery, an index of mitochondrial oxidative phosphorylation, is reduced in diabetic patients with lower extremity complications

OBJECTIVE To identify differences in postexercise phosphocreatine (PCr) recovery, an index of mitochondrial function, in diabetic patients with and without lower extremity complications. METHODS We enrolled healthy control subjects and three groups of patients with type 2 diabetes mellitus: without complications, with peripheral neuropathy, and with both peripheral neuropathy and peripheral arterial disease. We used magnetic resonance spectroscopic measurements to perform continuous measurements of phosphorous metabolites (PCr and inorganic phosphate [Pi]) during a 3-minute graded exercise at the level of the posterior calf muscles (gastrocnemius and soleus muscles). Micro- and macrovascular reactivity measurements also were performed. RESULTS The resting Pi/PCr ratio and PCr at baseline and the maximum reached during exercise were similar in all groups. The postexercise time required for recovery of Pi/PCr ratio and PCr levels to resting levels, an assessment of mitochondrial oxidative phosphorylation, was significantly higher in diabetic patients with neuropathy and those with both neuropathy and peripheral arterial disease (P < .01 for both measurements). These two groups also had higher levels of tumor necrosis factor-α (P < .01) and granulocyte colony-stimulating factor (P < .05). Multiple regression analysis showed that only granulocyte colony-stimulating factor, osteoprotegerin, and tumor necrosis factor-α were significant contributing factors in the variation of the Pi/PCr ratio recovery time. No associations were observed between micro- and macrovascular reactivity measurements and Pi/PCr ratio or PCr recovery time. CONCLUSIONS Mitochondrial oxidative phosphorylation is impaired only in type 2 diabetes mellitus patients with neuropathy whether or not peripheral arterial disease is present and is associated with the increased proinflammatory state observed in these groups.

Foot Muscle Energy Reserves In Diabetic Patients Without And With Clinical Peripheral Neuropathy

OBJECTIVE To investigate changes in the foot muscle energy reserves in diabetic non-neuropathic and neuropathic patients. RESEARCH DESIGN AND METHODS We measured the phosphocreatinine (PCr)/inorganic phosphate (Pi) ratio, total 31P concentration, and the lipid/water ratio in the muscles in the metatarsal head region using MRI spectroscopy in healthy control subjects and non-neuropathic and neuropathic diabetic patients. RESULTS The PCr/Pi ratio was higher in the control subjects (3.23 ± 0.43) followed by the non-neuropathic group (2.61 ± 0.36), whereas it was lowest in the neuropathic group (0.60 ± 1.02) (P < 0.0001). There were no differences in total 31P concentration and lipid/water ratio between the control and non-neuropathic groups, but both measurements were different in the neuropathic group (P < 0.0001). CONCLUSIONS Resting foot muscle energy reserves are affected before the development of peripheral diabetic neuropathy and are associated with the endothelial dysfunction and inflammation.

Management of the Diabetic Foot

Limb salvage, when dealing with the diabetic foot, deals with the ability to avoid amputation. This goal is carried out through three main aspects of diabetic care: identification of the “at-risk” foot, successful treatment of the acutely involved foot, and prevention of further problems. At each of these junctures patient education plays a vital role. A comprehensive program of diabetic foot management must include each of these aspects to successfully achieve limb salvage.