Effect of pancreatic and/or renal transplantation on diabetic autonomic neuropathy

Management of diabetic neuropathy

Diabetic neuropathy is a neurodegenerative disorder that may alter both the somatic and autonomic peripheral nervous systems in the context of diabetes mellitus (DM). It is a prevalent and burdensome chronic complication of DM, that requires timely management. Optimized glycemic control (mainly for type 1 DM), multifactorial intervention (mainly for type 2 DM), with lifestyle intervention/physical exercise, and weight loss represent the basis of management for diabetic distal symmetrical polyneuropathy, and should be implemented early in the disease course. Despite better understanding of the pathogenetic mechanisms of diabetic peripheral neuropathy, there is still a stringent need for more pathogenetic-based agents that would significantly modify the natural history of the disease. The paper reviews the available drugs and current recommendations for the management of distal symmetrical polyneuropathy, including pain management, and for diabetic autonomic neuropathy. Evaluation of drug combinations that would perhaps be more efficient in slowing the progression of the disease or even reversing it, and that would provide a better pain management is still needed.

Cardiac Autonomic Neuropathy Is Not Reversed by Euglycemia Following Islet Transplantation

BACKGROUND

Cardiac autonomic neuropathy (CAN) is a significant cause of morbidity and mortality for people with type 1 (T1D) and type 2 (T2D) diabetes. Heart rate variability (HRV) has been shown to be a marker of CAN with 24-hour Holter monitoring being a robust modality to assess HRV.

METHODS

To investigate the impact of hypoglycemia on CAN and its potential reversibility with islet transplantation, we compared HRV assessment by 24-hour Holter monitor on a total of 109 subjects from 5 cohorts: (1) T1D with recurrent severe hypoglycemia and on waiting list for islet transplant, (2) T1D following islet cell transplantation (ICT), (3) T2D without hypoglycemia, (4) individuals with prediabetes, and (5) controls without diabetes. SD of the normal-normal interval, square root of the mean squared differences of successive normal-normal intervals (rMSSD) and total spectral power were analyzed.

RESULTS

There was no significant difference in HRV parameters between T1D subjects and T1D post ICT suggesting CAN is not reversible at a median of 4 years postislet transplant. There was a significant difference in controls and T1D in rMSSD and between controls and T2D in total power. The differential effect on rMSSD in T1D and T2D suggests potential greater impact of hypoglycemia on rMSSD.

CONCLUSIONS

Achieving euglycemia after ICT may not reverse CAN once established with no significant difference in HRV parameters at a median of 4 years postislet transplant. Differential effects of T1D as compared with T2D on CAN were identified.

Neurologic complications of pancreas and small bowel transplantation

In the past decade, substantial improvements in patient and graft survival for pancreas and small bowel transplants have been achieved. Despite this progress, many patients still develop neurologic complications in the course of their illness. Small bowel transplants produce more neurologic complications because of the complex metabolic environment in which the procedure is performed and because of the intense immune suppression necessitated by the greater immunogenicity of the intestinal mucosa. Pancreas transplants stabilize and/or improve the signs and symptoms of diabetic neuropathy over time. Because transplantation of the pancreas is often coupled with a kidney transplant and small intestine with liver, neurologic complications in these patients sometimes reflect problems involving the organ partner or both organs. The spectrum of neurologic complications for pancreas and small bowel transplant recipients is similar to other organ transplants but their frequency varies depending on the type of transplant performed.

Regression and progression of cardiac sympathetic dysinnervation complicating diabetes: an assessment by C-11 hydroxyephedrine and positron emission tomography

Cardiovascular denervation complicating diabetes has been implicated in sudden cardiac death potentially by altering myocardial electrical stability and impairing myocardial blood flow. Scintigraphic evaluation of cardiac sympathetic integrity has frequently demonstrated deficits in distal left ventricular (LV) sympathetic innervation in asymptomatic diabetic subjects without abnormalities on cardiovascular reflex testing. However, the clinical significance and subsequent fate of these small regional defects is unknown. This study reports the results of a prospective observational study in which positron emission tomography (PET) with (-)-[11C]-meta-hydroxyephedrine ([11C]-HED) was used to evaluate the effects of glycemic control on the progression of small regional LV [11C]-HED retention deficits in 11 insulin-dependent diabetic subjects over a period of 3 years. The subjects were divided into two groups based on attained glycemic control during this period: group A contained six subjects with good glycemic control (individual mean HbA1c <8%), and group B contained five subjects with poor glycemic control (individual mean HbAlc > or =8%). Changes in regional [11C]-HED retention were compared with reference values obtained from 10 healthy aged-matched nondiabetic subjects. At baseline, abnormalities of [11C]-HED retention affected 7.3%+/-1.4% and 9.9%+/-6.6% of the LV in group A and B subjects, respectively, with maximal deficits of LV [ C]-HED retention involving the distal myocardial segments. At the final assessment in group A, the extent of the deficits in [11C]-HED retention decreased to involve only 1.7%+/-0.7% of LV (P<.05 v. baseline scan), with significant increases in [11C]-HED retention occurring in both the distal and proximal myocardial segments. In contrast, in group B with poor glycemic control, the extent of [11C]-HED deficits increased to involve 34%+/-3.5% of the LV (P<.01 v. baseline), with retention of [11C]-HED significantly decreasing in the distal segments ([11C]-HED retention index, 0.066+/-0.003 v. 0.057+/-0.002, P<.05, at baseline and final assessment, respectively). Poor glycemic control was associated with increased heterogeneity of LV [11C]-HED retention, since three of five group B subjects developed abnormally increased [11C]-HED retention in the proximal myocardial segments. In conclusion, defects in LV sympathetic innervation can regress or progress in diabetic subjects achieving good or poor glycemic control, respectively. In diabetic subjects with early cardiovascular denervation, institution of good glycemic control may prevent the development of myocardial sympathetic dysinnervation and enhanced cardiac risk.

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.

Three-year follow-up on scintigraphically assessed cardiac sympathetic denervation in patients with long-term insulin-dependent (type I) diabetes mellitus

Scintigraphy using I-123-metaiodobenzylguanidine (I-123-MIBG) and Tc-99m-methoxyisobutylisonitrile (Tc-99m-MIBI) allows assessment of the cardiac sympathetic innervation and the myocardial perfusion. To investigate the natural history of cardiac sympathetic denervation in long-term diabetic patients without myocardial perfusion defects, global and regional I-123-MIBG and Tc-99m-MIBI uptake was determined (score 1-6; 1 = normal uptake, 6 = no uptake) in 22 patients with insulin-dependent (type I) diabetes mellitus (IDDM) at 3-year follow-up. All patients were treated with intensive insulin therapy and HbA1c was 8.0% +/- 1.0% at entry compared with 7.9% +/- 1.1% at follow-up. Cardiac sympathetic denervation (I-123-MIBG uptake score > 2), initially observed in 18 patients, was detectable in 21 patients at follow-up. The global myocardial I-123-MIBG uptake score deteriorated in eight patients, remained unchanged in 11 and improved in three patients. The changes in mean global I-123-MIBG uptake score (3.5 +/- 1.0 versus 3.8 +/- 0.8) were not significant. Reduction of the anterior, lateral, posterior, septal, and apical I-123-MIBG uptake did not progress significantly during follow-up. The mean uptake score of the posterior myocardial region (4.7 +/- 0.8) was smaller than the uptake score of the anterior (3.0 +/- 1.1, p = 0.001), lateral (3.2 +/- 0.9, p < 0.001) and septal (4.1 +/- 1.1, p < 0.05) myocardial regions. At follow-up, moderate myocardial perfusion defects (global Tc-99m-MIBI uptake score = 3) were detectable in four patients. Our study demonstrates that scintigraphically assessed cardiac sympathetic denervation does neither significantly regress nor progress on the average in a group of long-term IDDM patients during a 3-year follow-up. Thus, it is concluded that cardiac sympathetic abnormalities are a persistent, yet frequent phenomenon in long-term IDDM patients.

C-peptide improves autonomic nerve function in IDDM patients

In order to determine the possible influence of C-peptide on nerve function, 12 insulin-dependent diabetic (IDDM) patients with symptoms of diabetic polyneuropathy were studied twice under euglycaemic conditions. Tests of autonomic nerve function (respiratory heart rate variability, acceleration and brake index during tilting), quantitative sensory threshold determinations, nerve conduction studies and clinical neurological examination were carried out before and during a 3-h i.v. infusion of either C-peptide (6 pmol.kg-1.min-1) or physiological saline solution in a double-blind study. Plasma C-peptide concentrations increased from 0.11 +/- 0.02 to 1.73 +/- 0.04 nmol/l during C-peptide infusion. Clinical neurological examination quantitative sensory threshold evaluations and nerve conduction measurements failed to detect significant changes between C-peptide and saline study periods. Respiratory heart rate variability increased significantly from 13 +/- 1 to 20 +/- 2% during C-peptide infusion (p < 0.001), reaching normal values in five of the subjects; control studies with saline infusion did not alter the heart rate variability (basal, 14 +/- 2; saline, 15 +/- 2%). A reduced brake index value was found in seven patients and increased significantly during the C-peptide infusion period (4.6 +/- 1.0 to 10.3 +/- 2.2%, p < 0.05) but not during saline infusion (5.9 +/- 2 to 4.1 +/- 1.1%, NS). It is concluded that short-term (3-h) infusion of C-peptide in physiological amounts may improve autonomic nerve function in patients with IDDM.

Pancreas transplantation

Vascularized pancreas transplantation has assumed an increasing role in the treatment of diabetes mellitus. Through 1994, over 6000 pancreas transplants had been performed worldwide, with over 80% being combined pancreas-kidney transplants. Overall 1-year patient survival exceeds 90% and graft survival (complete insulin independence) exceeds 70%. Although successful pancreas transplantation achieves euglycemia and complete insulin independence, this occurs at the expense of hyperinsulinemia and chronic immunosuppression. The net effect of these changes on diabetic complications in the long term remains to be determined. In the short term, improvement in the quality of life and possible prevention of further morbidity associated with diabetes makes pancreas transplantation an important therapeutic option, particularly when combined with a kidney transplant, in appropriately selected diabetic patients.

Pancreas transplantation for diabetes mellitus

Vascularized pancreas transplantation has assumed an increasing role in the treatment of diabetes mellitus. Through 1993, over 5500 pancreas transplants have been performed worldwide, with over 80% being combined pancreas-kidney transplants. Overall one-year patient survival exceeds 90% and graft survival (complete insulin independence) exceeds 70%. Although successful pancreas transplantation achieves euglycemia and complete insulin independence, this occurs at the expense of hyperinsulinemia and chronic immunosuppression. The net result of these changes on diabetic complications in the long term remains to be determined. In the short term, improvement in the quality of life and possible prevention of further morbidity associated with diabetes makes pancreas transplantation an important therapeutic option, particularly when combined with a kidney transplant, in appropriately selected diabetic patients.

Hyperglycemia induces abnormalities of gastric myoelectrical activity in patients with type I diabetes mellitus

BACKGROUND/AIMS

Blood glucose concentration has been shown to be an important factor in gastric motility. However, the effect of hyperglycemia on gastric myoelectrical activity has not yet been studied in patients with diabetes.

METHODS

Surface electrogastrography was performed in eight patients with type I diabetes mellitus under normoglycemic and hyperglycemic conditions (glucose clamp technique) and in eight normoglycemic control subjects.

RESULTS

In the early postprandial state, the frequency of the normal pacemaker rhythm tended to be higher during hyperglycemia than during normoglycemia (3.10 +/- 0.27 vs. 2.92 +/- 0.19 cycle/min; P = 0.061). The frequency decrease that occurs immediately after a meal was found less frequently during hyperglycemia (in 25% vs. 75% of the patients; P = 0.046). Higher harmonics of the 3-cycle/min component, indicating an electrogastrographic waveform change, were found less often during hyperglycemia (in 13% vs. 63% of the patients; P = 0.039). Dysrhythmias (in particular, tachygastrias) were more prevalent during hyperglycemia (40.6% vs. 6.5% of the time; P = 0.028). No differences were found between normoglycemic patients and control subjects.

CONCLUSIONS

This study has shown that hyperglycemia is an important factor in the generation of gastric myoelectrical disturbances and tachygastrias in particular.