Increased nerve conduction in diabetics after a year of improved glucoregulation

Composite nerve conduction scores and signs for diagnosis and somatic staging of diabetic polyneuropathy: Mid North American ethnic cohort survey

INTRODUCTION/AIMS

In the Diabetes Control and Complications Trial (DCCT), the minimal nerve conduction (NC) criterion for diabetic sensorimotor polyneuropathy (DSPN) was abnormality of NC in more than one peripheral nerve without specifying the attributes of NCs to be evaluated. In the present study, we assess individual and composite scores of NCs meeting the DCCT criterion and signs for improved diagnosis and assessment of DSPN severity.

METHODS

Evaluated were 13 attributes and 6 composite NC scores and signs and symptoms in 395 healthy subjects (HS) and 388 persons with diabetes (DM).

RESULTS

Percent abnormality between subjects with DM and HS was remarkably different among individual attributes and the six composite NC scores. For diagnosis of DSPN using the DCCT criterion, assessment of conduction velocities (CVs) and distal latencies (DLs) provided sensitive diagnoses of DSPN. NC amplitudes provided stronger measures of severity. In studied cohorts, DSPN was staged: N0, no NC abnormality using NC score 2 (CVs and DLs), 60.0%; N1, NC abnormality only, 18.4%; N2, NC abnormality and signs of feet or legs, 16.3%; and N3, NC abnormality and signs of thighs, 5.3%.

DISCUSSION

For sensitive and standard diagnosis of DSPN using the DCCT NC criterion, specifically defined composite scores of CVs and DLs, e.g., score 2, is recommended. A composite score of amplitudes, e.g., score 4, provides a stronger measure of neuropathy severity. Also, provided are HS reference values of evaluated attributes of NCs and estimates of staged severity of DSPN of mid North American DM cohorts.

Favorable impact of a vegan diet with exercise on hemorheology: implications for control of diabetic neuropathy

A little-noticed clinical report indicates that a low-fat, whole-food vegan diet, coupled with daily walking exercise, leads to rapid remission of neuropathic pain in the majority of type 2 diabetics expressing this complication. Concurrent marked improvements in glycemic control presumably contribute to this benefit, but are unlikely to be solely responsible. Consideration should be given to the possibility that improved blood rheology - decreased blood viscosity and increased blood filterability - plays a prominent role in mediating this effect. There is considerable evidence that neural hypoxia, secondary to impaired endoneurial microcirculatory perfusion, is a crucial etiologic factor in diabetic neuropathy; the unfavorable impact of diabetes on hemorheology would be expected to exacerbate endoneurial ischemia. Conversely, measures which improve blood fluidity would likely have a beneficial impact on diabetic neuropathy. There is indeed evidence that vegan diets, as well as exercise training, tend to decrease the viscosity of both whole blood and plasma; reductions in hematocrit and in fibrinogen may contribute to this effect. The fact that vegan diets decrease the white cell count is suggestive of an improvement in blood filterability as well; filterability improves with exercise training owing to an increase in erythrocyte deformability. Whether these measures influence the activation of leukocytes in diabetics - an important determinant of blood filterability - remains to be determined. There are various reasons for suspecting that a vegan diet can reduce risk for other major complications of diabetes - retinopathy, nephropathy, and macrovascular disease - independent of its tendency to improve glycemic control in type 2 patients. The vegan diet/exercise strategy represents a safe, 'low-tech' approach to managing diabetes that deserves far greater attention from medical researchers and practitioners.

Long-term effects of pancreatic transplantation on diabetic neuropathy

Restoration of a long-lasting euglycemic state by a functioning pancreatic transplantation (PTx) is the most logical treatment for insulin-dependent diabetes mellitus and for amelioration of secondary complications, including neuropathy. We evaluated neurological function by clinical examination, nerve conduction studies, and autonomic function tests in 115 patients with a functioning PTx and in 92 control patients treated with insulin, at baseline and 1, 2, 3.5, 5, 7, and 10 years later. In control patients, neuropathy progressively worsened during follow-up. The clinical examination score and composite indices of abnormality of motor and sensory nerve conduction decreased significantly at all intervals tested. Autonomic function indices also decreased, but significantly only after 1 year. In patients who received a successful PTx the neuropathy improved. The motor and sensory nerve conduction indices increased significantly at all intervals after transplantation, whereas the clinical examination and autonomic tests improved only slightly. Patients who received either a PTx alone, a PTx after a kidney graft, or simultaneous pancreatic and kidney transplantations improved similarly over the follow-up. These results indicate that a functioning PTx halts the progression and improves the signs of diabetic polyneuropathy by restoration of a normoglycemic state.

Nerve conduction and autonomic nerve function in diabetic children. A 10-year follow-up study

In order to study the long-term development of diabetic neuropathy in children with newly diagnosed diabetes mellitus, 144 children were entered in a prospective study of nerve conduction and autonomic nervous function. Neurophysiological recordings of nerve conduction and parasympathetic function (R-R variations) were made at onset of diabetes and after 2, 5 and 10 years. Low sensory nerve conduction and autonomic dysfunction were found in approximately 25% of the children at onset of diabetes when the patients were not yet in complete remission. During years 0-2, an initial improvement of sensory conduction velocities was found. After 2 years, deteriorations in sensory and motor nerve conduction and autonomic nerve function were common and further deterioration was seen over time. A correlation was found between nerve conduction and glycaemic control.

Diabetic complications. The importance of glucose control

The most important question for clinicians caring for diabetic patients, and for the patient themselves, is whether the risk of complications can be altered by careful control of glycemia. Epidemiologic studies showed a strong relationship between glycemia and diabetic complications, in both type I and type II diabetes. There is a continuous relationship between prevailing glycemia and risk of progression of complications, implying that any improvement in glycemic control is beneficial. The debate of the question has ended--glucose control is important.

Peripheral, but not central, nervous system abnormalities are reversed by pancreatic islet transplantation in diabetic Lewis rats

Neuroelectrophysiological recordings represent a non-invasive and reproducible method of detecting central and peripheral nervous system alterations in diabetes mellitus. In order to evaluate whether the normalization of metabolic control obtained by pancreatic islet transplantation could reverse diabetic neuroelectrophysiological alterations, or prevent further deterioration, we used an experimental model in which pancreatic islets (n = 1200) were injected into the portal vein of inbred Lewis rats (used as islet donors as well as recipients). Islets were injected 4 months after diabetes induction, since previous work had shown functional but not morphological damage at the nervous tissue level at this stage of the disease. Visual (V), brainstem auditory (BA) and somatosensory (S) evoked potentials (EPs) were measured in streptozotocin-induced, islet-recipient diabetic rats (n = 7), streptozotocin-induced diabetic rats (n = 16) and non-diabetic control rats (n = 12). Metabolic parameters and electrophysiological recordings were evaluated before diabetes induction, before transplantation and 4 months later. After transplantation, glycaemic levels returned to normal values within 1 week and remained so until the end of the study, as confirmed by a normal oral glucose tolerance test and by an increase in body weight. Electrophysiological recordings were altered in diabetic animals before transplantation. Four months after transplantation EP recordings improved, with a detectable gradient from the peripheral to the central structures. SEPs were significantly improved in the peripheral tarsus-L6 tract and the L6-cortex tract (P < 0.005 and P < 0.01 versus diabetic rats) and were ameliorated without achieving statistical significance in the central L6-cortex tract. BAEP latency values tended to improve in transplanted rats, but the differences versus non-transplanted diabetic animals failed to reach significance. VEP values remained clearly pathological and even deteriorated after transplantation. These results show that normalization of metabolic control by pancreatic islet transplantation can reverse some of the already established neuroelectrophysiological alterations at the peripheral nervous system level, but does not affect other alterations at the central nervous system level.

Autonomic dysfunction in newly diagnosed insulin-dependent diabetes mellitus children

In order to evaluate the presence of electrophysiologic signs of autonomic dysfunction (AD) in newly diagnosed diabetic children, cardiovascular reflex tests were performed in 55 (30 female, 25 male) newly diagnosed insulin-dependent diabetes mellitus (IDDM) patients aged 10.3-20.7 years (mean +/- S.D.: 15.2 +/- 5.6). Ten (18.2%) diabetic children had cardiovascular AD, defined as abnormal results in 2 of 5 tests. Autonomic function tests were assessed at entry and after 12, 24, and 36 months of the study. All diabetic children received human insulin and followed an intensive insulin treatment (3 or 4 injections per day), associated with a teaching program of self-management of the disease. In the 3 years of follow-up, all children improved the quality of metabolic control (glycosylated hemoglobin, HbA1c: 10.3 +/- 1.1% versus 7.7 +/- 0.9; P < .01) and manifested no significant difference between baseline and follow-up values of autonomic function tests which remained unchanged in spite of this improvement. Cardiovascular autonomic dysfunction can be present in newly diagnosed IDDM children and it seems to be stable in children who follow an intensive insulin injection therapy.

Single-fiber electromyography in diabetic peripheral polyneuropathy

In this study we examined the value of single-fiber electromyography (SFEMG) in assessing the degree of reinnervation in diabetic patients with clinical neuropathy. Relationships between reinnervation and the degree of metabolic control, and/or duration of diabetes were examined. Thirty-six insulin-dependent diabetics and 54 non-insulin-dependent diabetics underwent SFEMG examination of the tibialis anterior muscle, as well as conventional nerve conduction studies of the upper and lower limbs. All patients examined exhibited some abnormality of SFEMG even in the presence of normal nerve conduction studies found in 18% of patients. In diabetic patients, the jitter in the tibialis anterior muscle correlated positively with glycosylated hemoglobin; whereas lower limb nerve conduction studies did not correlate with this measure of diabetic control. These data suggest that SFEMG is a sensitive measure of nerve function and reinnervation and that it may reflect the dynamic changes in metabolic status in diabetic patients.

The efficacy of aldose reductase inhibitors in the management of diabetic complications. Comparison with intensive insulin treatment and pancreatic transplantation

Recently, aldose reductase inhibitors (ARIs) have been registered in several countries for the improvement of glycaemic control. However, their efficacy is still controversial. ARIs inhibit the enhanced flux of glucose through the polyol pathway. As such, they can never be more effective than normoglycaemia, and so their potential benefits and limitations should be considered relative to the effects of prolonged euglycaemia. The clinical effects of ARIs can be put into perspective by assessing the effects of improved glycaemic control attained in randomised trials of intensive insulin treatment [such as the Diabetes Control and Complications Trial (DCCT)] and after pancreatic transplantation. Although direct comparison of these 3 interventions is hampered by differences in patient populations, duration and methods of follow-up and in the potency of ARIs, the effects of these 3 metabolic interventions and their course in time appear remarkably similar. For neuropathy, all 3 interventions induce an increase in average motor nerve conduction velocity of approximately 1 m/sec during the first months of treatment. At the same time, improvement of painful symptoms may occur. These changes probably largely represent a metabolic amelioration of the condition of the nerves. Around the second year of treatment with all 3 forms of metabolic improvement, an acceleration of nerve conduction of a similar magnitude occurs, with signs of structural nerve regeneration and some sensory recuperation. Experience with ARIs in nephropathy is still limited, but similar improvements in glomerular filtration rate and, less consistently, in urinary albumin excretion were found during short term normoglycaemia produced by all 3 forms of treatment. Comparison of a small number of studies, however, shows differences between intensive insulin regimens, pancreatic transplantation and ARIs in effects on retinopathy. Retinopathy often temporarily deteriorates in the early phases of improved glycaemic control, but this is not noted with ARIs. New microaneurysm formation was slightly reduced in a single long term study with the ARI sorbinil, but the preventive effects on the overall levels of retinopathy seemed less strong than in normoglycaemia trials of similar duration. However, the pharmacodynamic effects on inhibiting the polyol pathway differ among ARIs, and the half-life of the inhibiting effect of sorbinil may have been too short for a complete reduction of polyol pathway activity. The trials of prolonged intensive insulin therapy and pancreatic transplantation have demonstrated that very strict metabolic control must be maintained continuously for many years before a significant reduction of complications can be demonstrated.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of 8 years of strict glycaemic control on peripheral nerve function in IDDM patients: the Oslo Study

We have investigated the effect of long-term strict glycaemic control on peripheral and autonomic nerve function in 45 IDDM patients (age 18-42 years, diabetes duration 7-23 years) without clinical signs of neuropathy or other neurological disease. They were randomly assigned to treatment either with continuous insulin infusion, multiple injections (4-6 times daily), or conventional treatment (twice daily) for 4 years and followed prospectively for 8 years. Motor and sensory nerve conduction velocities were measured at the start and after 8 years. Autonomic nerve function tests were performed only once, after 8 years. A significant reduction of nerve conduction velocity was observed during 8 years in patients with mean HbA1 more than 10% (n = 12, group mean 10.9%, range 10.1-13.2%) compared to patients with HbA1 less than 10% (n = 33, group mean 9.0%, range 7.5-9.9%). Change of motor nerve conduction velocity in the peroneal nerve was: -4.8 +/- 4.9 (SD) vs -2.2 +/- 5.3 m/s (p < 0.01). Change of motor nerve conduction velocity in the posterior tibial nerve was: -6.8 +/- 5.7 vs- 3.9 +/- 5.1 m/s (p < 0.05). No significant changes were observed in the ulnar nerve. Change of sensoric nerve conduction velocity in the sural nerve was: -8.9 +/- 8.0 vs -4.6 +/- 5.3 m/s (p < 0.05). Multiple regression analysis showed that a change in HbA1 of 1% resulted in a 1.3 m/s change in nerve conduction velocity during 8 years.(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary bladder dysfunction in the BB/W diabetic rat: effect of ganglioside treatment on functional and structural alterations

Urinary bladder dysfunction in the diabetic BB/W rat is characterized by infrequent irregular contractions of high amplitude. Initially these occur in the absence of detectable neuroanatomical lesions of sensory afferent and parasympathetic fibers of the pelvic nerve, which constitute the micturition reflex arc. Structural lesions consisting of progressive axonal atrophy of myelinated and unmyelinated fibers become detectable only after 4 months of diabetes. In the current study we evaluated the effect of ganglioside treatment (10 mg./kg. body weight) for one month. This drug regimen was initiated at 4 months of diabetes, when functional bladder abnormalities were well established, whereas structural lesions were yet to appear. Animals examined 1 or 3 months after termination of the one-month treatment protocol showed sustained normalization of the characteristic functional abnormalities, accompanied by prevention of the neuroanatomical lesions of sensory afferent and parasympathetic efferent myelinated fibers in the pelvic nerve. These data suggest that ganglioside treatment may be beneficial in delaying the progression of diabetic autonomic neuropathy in this experimental animal model.

Effects of methylcobalamin on diabetic neuropathy

We studied the clinical and neurophysiological effects of methylcobalamin on patients with diabetic neuropathy. In a double-blind study, the active group showed statistical improvement in the somatic and autonomic symptoms with regression of signs of diabetic neuropathy. Motor and sensory nerve conduction studies showed no statistical improvement after 4 months. The drug was easily tolerated by the patients and no side effects were encountered.

Is hyperglycemia risky enough to justify the increased risk of hypoglycemia linked with tight diabetes control?

There is an ongoing debate about the possible disadvantages of human insulin use with respect to a possibly lower awareness of hypoglycemia than is associated with animal insulin usage. Participants in this debate have not, however, discussed a major contributory factor to this life-threatening acute complication of diabetes, the pressure on patients to achieve normal levels of blood glucose. This pressure stems from the view that hyperglycemia is the major causative factor in the long-term diabetic complications. However, the evidence that supranormal levels of tissue and plasma glucose contribute to the diabetic tissue damage is not as strong as the arguments on behalf of this position. Indeed, elevated glycemia may be no more than a crude index of other, unknown metabolic derangements which may be causative agents in diabetes-associated tissue damage. Intensive efforts to "normalize" glycemia lack experimental and clinical justification, distract attention from other possible mechanisms, and may impose an unnecessary risk on the insulin-dependent diabetic population since intensive "normalization" of glycemia lowers hypoglycemia awareness, and thus increases risk of hypoglycemia, irrespective of the type of insulin used.

Effects of pancreatic transplantation on diabetic neuropathy

Reestablishment of the euglycemic state by successful transplantation of the pancreas might halt or reverse diabetic neuropathy. To test this possibility we evaluated neurologic function by clinical examination, nerve conduction studies, and autonomic-function tests in patients with insulin-dependent (Type I) diabetes mellitus before and after successful pancreatic transplantation. Sixty-one patients were studied before and 12 months after transplantation, 27 again after 24 months, and 11 again after 42 months. A control group of patients with Type I diabetes treated with insulin underwent the same studies at similar intervals--48 patients before and after 12 months had elapsed, 21 again after 24 months, and 12 again after 42 months. In the control group, neuropathy tended to worsen during the follow-up period. The scores on the clinical examination indicated increased impairment after 12 months. Composite indexes of the degree of abnormality found on neurophysiologic testing of the function of peripheral motor, sensory, and autonomic nerves indicated decreased autonomic function after 12 months. The examination score and the three index values worsened slightly but not significantly in the patients followed for 24 and 42 months. In contrast, in the patients who had received pancreatic transplants, the neuropathy tended to improve. There was significant improvement in the motor and sensory indexes 12 months after transplantation and in the sensory index 24 months after transplantation. The other measures improved slightly but not significantly at these times, as did all four measures in the patients studied 42 months after transplantation. We conclude that the progression of diabetic polyneuropathy may be halted through the restoration of a euglycemic state by successful pancreatic transplantation.

A self-controlled study of the effect of continuous subcutaneous insulin infusion on diabetic neuropathy

Ten patients with poorly controlled type I diabetes mellitus and a documented complication of their disease were observed during 6 months of conventional diabetic management followed by 6 months of insulin infusion pump treatment and home blood glucose monitoring. Median nerve conduction velocity (NCV) was inversely correlated with the glycosylated hemoglobin (HbA1c) level at entry into the study (r = 0.71; P less than 0.05). The mean HbA1c value at the end of the conventional treatment period was 14.3% and fell to 10.1% by completion of the pump treatment period (P less than 0.0001). The median NCV was significantly greater at the completion of the infusion treatment period than it was at the end of the conventional management portion of the study. However, the rate of increase in NCV during the infusion period was not greater than the rate established during the prior treatment period. In addition, change in HbA1c levels during the pump treatment period did not correlate with change in conduction velocity for any of the nerves studies. These results from a self-controlled study of continuous subcutaneous insulin infusion indicate that improved blood glucose control without normalization of metabolic parameters is not sufficient to reverse the functional deterioration of large, fast-conducting nerve fibers that occurs in type I diabetes.

Comparison of the effects of continuous subcutaneous infusion and split-mixed injection of insulin on nerve function in type I diabetes mellitus

Comparable groups of type I diabetic patients (n = 19) were matched for age, duration of diabetes, mean HbA1 values, insulin requirements, degree of neuropathy, and the mean of nerve conduction velocities (CV) in median, ulnar, and peroneal motor and median, ulnar, and sural sensory nerves. One group (n = 9) was managed with continuous subcutaneous infusion of (regular) insulin (CSII); the other (n = 10) with split-mixed injections of (intermediate and regular) insulin (SMII). After 12 months, glucose regulation was equally and significantly improved in both groups (P less than 0.005), although it was not sufficiently intense to normalize mean total glycosylated hemoglobin values in either group. Furthermore treatment produced no difference between groups in the values for mean amplitude of glycemic excursions, 12 month average of consecutive M-values or in clinical evaluation. However, in the CSII group, mean CV had increased 6.4% (2.75 + 0.56 m/s; mean +/- SEM) versus 1.3% (0.57 +/- 0.54 m/s) in the SMII group (P less than 0.005). Multivariate analysis on a nerve-by-nerve basis found significantly improved conduction in 2/6 nerves (median motor; ulnar sensory) in the CSII group compared to the SMII group. These results suggest that CSII may provide a more favorable microenvironment for nerve repair.

Peripheral nerve function in patients with painful diabetic neuropathy treated with continuous subcutaneous insulin infusion

In order to study the effects of improved metabolic control on painful diabetic polyneuropathy, 15 patients were treated with continuous subcutaneous insulin infusion over a 12 month period. Polyneuropathy was assessed by pain score, neurological examinations, nerve conduction studies and determination of sensory thresholds and cardiovascular reflexes. Improved metabolic control was confirmed by significantly improved levels of glycosylated haemoglobin (11.7 +/- 0.3% at entry to the study, to 8.7 +/- 0.3% after 12 months; mean +/- SEM). Symptomatic relief was confirmed by significantly improved pain scores. Thresholds for thermal cutaneous sensation improved significantly from 6.0 +/- 0.8 degrees C at entry to the study to 2.7 +/- 0.7 degrees C after 12 months (mean +/- SEM). These findings suggest a selective improvement of peripheral small nerve fibre function after continuous subcutaneous insulin infusion. The importance of quantitating thermal cutaneous sensation in longitudinal studies of patients with diabetic neuropathy was confirmed.