Evidence for reversibility of defective counterregulation in a patient with insulinoma

Evaluation of plasma cortisol during fasting test in patients with endogenous hyperinsulinemic hypoglycemia. Fifteen years experience

BACKGROUND

Endogenous hyperinsulinemic hypoglycemia (EHH) is a rare clinical condition. The aim of this study was to evaluate baseline plasma cortisol concentration and its concentration during hypoglycemic crisis in fasting tests (FT) performed in our center. Secondarily, the aim was to establish the relationship between baseline cortisol and the time of evolution of EHH.

MATERIAL AND METHODS

A retrospective, observational, descriptive study was carried out which included patients with hypoglycemic disorder with positive FT.

RESULTS

Of a total of 21 patients, 16 presented insulinoma, 1 nesidioblastosis, 2 malignant insulinoma and 2 EHH without pathological diagnosis. The time from the onset of symptoms to diagnosis was 2 years (Q1=1.5-Q2=5.5). The comparison between median baseline cortisol (BC)=11.8 mcg/dl (nmol/L 340.68) (Q1=9-Q3=14.1) and median cortisol during hypoglycemic episode (HC)=11.6 mcg/dl (nmol/L: 303.44) (Q1=7.8-Q3=16.1) showed no differences (Z=-0.08; P>.05). When correlating BC with HC, no significant relationship was observed (r=0.16; P>.05). When correlating the glycemic value in the crisis and the HC, a slight negative trend was found (r=-0.53; P=.01). In addition, we found that recurrent hypoglycemic disorder is associated with lower baseline cortisol values ​​the longer the time of its evolution.

CONCLUSION

We confirmed that cortisol values ​​remain low during hypoglycemic episodes, reinforcing the hypothesis of lack of response of this counterregulatory hormone in cases of recurrent hypoglycemia.

Cognitive, neurophysiologic and metabolic sequelae of previous hypoglycemic coma revealed by hyperinsulinemic-hypoglycemic clamp in type 1 diabetic patients

To examine the relationship between electroencephalographic (EEG) activity and hypoglycemia unawareness, we investigated early parameters of vigilance and awareness of various symptom categories in response to hypoglycemia in intensively treated type 1 diabetic (T1DM) patients with different degrees of hypoglycemia unawareness. Hypoglycemia was induced with a hyperinsulinemic-hypoglycemic clamp in six T1DM patients with a history of hypoglycemia unawareness previous severe hypoglycemic coma (SH) and in six T1DM patients without (C) history of hypoglycemia unawareness previous severe hypoglycemic coma. Cognitive function tests (four choice reaction time), counterregulatory responses (adrenaline), and symptomatic responses were evaluated at euglycemia (90 mg/dl) and during step-wise plasma glucose reduction (68, 58 and 49 mg/dl). EEG activity was recorded continuously throughout the study and analyzed by spectral analysis. Cognitive function deteriorated significantly at a glucose threshold of 55 ± 1 mg/dl in both groups (p = ns) during hypoglycemia, while the glucose threshold for autonomic symptoms was significantly lower in SH patients than in C patients (49 ± 1 vs. 54 ± 1 mg/dl, p < 0.05, respectively). In SH patients, eye-closed resting EEG showed a correlation between the mean dominance frequency and plasma glucose (r = 0.62, p < 0.001). Theta relative power increased during controlled hypoglycemia compared to euglycemia (21.6 ± 6 vs. 15.5 ± 3% Hz p < 0.05) and was higher than in the C group (21.6 ± 6 vs. 13.8 ± 3%, p < 0.03). The cognitive task beta activity was lower in the SH group than in the C group (14.8 ± 3 Hz, vs. 22.6 ± 4 vs. p < 0.03). Controlled hypoglycemia elicits cognitive dysfunction in both C and SH patients; however, significant EEG alterations during hypoglycemia were detected mainly in patients with a history of hypoglycemia unawareness and previous severe hypoglycemic coma. These data suggest that prior episodes of hypoglycemic coma modulate brain electric activity.

Reversible Adrenal Insufficiency in Three Patients With Post-Roux-en-Y Gastric Bypass Noninsulinoma Pancreatogenous Hypoglycemia Syndrome

Objective. Noninsulinoma pancreatogenous hypoglycemia syndrome (NIPHS) is a disorder of endogenous hyperinsulinemia that is clinically distinguishable from insulinoma, with a greater preponderance after Roux-en-Y gastric bypass (RYBG). Hyperinsulinemic hypoglycemia can predispose to attenuation of counterregulatory hormone responses to hypoglycemia, and consequent suppression of the hypothalamic-pituitary-adrenal (HPA) axis. This case series describes 3 individuals who were diagnosed with adrenal insufficiency (AI) after undergoing RYGB, complicated by NIPHS. Methods. A retrospective chart review was performed for each individual. Chart review applied particular attention to the onset of hyperinsulinemic hypoglycemia following bariatric surgery and the dynamic testing leading to the diagnoses of NIPHS and AI. Results. In each case, reactive hypoglycemia ensued within months to years after RYGB. Cosyntropin stimulation testing confirmed the diagnosis of AI. Hydrocortisone therapy reduced the frequency and severity of hypoglycemia and was continued until successful medical and/or surgical management of hyperinsulinism occurred. Follow-up testing of the HPA axis demonstrated resolution of AI. In all cases, hydrocortisone therapy was finally discontinued without incident. Conclusion. We speculate that transient AI is a potential complication in patients who experience recurrent hyperinsulinemic hypoglycemia after RYGB. The putative mechanism for this observation may be attenuation of the HPA axis after prolonged exposure to severe, recurrent hypoglycemia. We conclude that biochemical screening for AI should be considered in individuals who develop post-RYGB hyperinsulinemic hypoglycemia. If AI is diagnosed, supportive treatment should be maintained until hyperinsulinemic hypoglycemia has been managed effectively.

Restoration of self-awareness of hypoglycemia in adults with long-standing type 1 diabetes: hyperinsulinemic-hypoglycemic clamp substudy results from the HypoCOMPaSS trial

OBJECTIVE

Impaired awareness of hypoglycemia (IAH) and defective counterregulation significantly increase severe hypoglycemia risk in type 1 diabetes (T1D). We evaluated restoration of IAH/defective counterregulation by a treatment strategy targeted at hypoglycemia avoidance in adults with T1D with IAH (Gold score ≥4) participating in the U.K.-based multicenter HypoCOMPaSS randomized controlled trial.

RESEARCH DESIGN AND METHODS

Eighteen subjects with T1D and IAH (mean ± SD age 50 ± 9 years, T1D duration 35 ± 10 years, HbA1c 8.1 ± 1.0% [65 ± 10.9 mmol/mol]) underwent stepped hyperinsulinemic-hypoglycemic clamp studies before and after a 6-month intervention. The intervention comprised the HypoCOMPaSS education tool in all and randomized allocation, in a 2 × 2 factorial study design, to multiple daily insulin analog injections or continuous subcutaneous insulin infusion therapy and conventional glucose monitoring or real-time continuous glucose monitoring. Symptoms, cognitive function, and counterregulatory hormones were measured at each glucose plateau (5.0, 3.8, 3.4, 2.8, and 2.4 mmol/L), with each step lasting 40 min with subjects kept blinded to their actual glucose value throughout clamp studies.

RESULTS

After intervention, glucose concentrations at which subjects first felt hypoglycemic increased (mean ± SE from 2.6 ± 0.1 to 3.1 ± 0.2 mmol/L, P = 0.02), and symptom and plasma metanephrine responses to hypoglycemia were higher (median area under curve for symptoms, 580 [interquartile range {IQR} 420-780] vs. 710 [460-1,260], P = 0.02; metanephrine, 2,412 [-3,026 to 7,279] vs. 5,180 [-771 to 11,513], P = 0.01). Glycemic threshold for deterioration of cognitive function measured by four-choice reaction time was unchanged, while the color-word Stroop test showed a degree of adaptation.

CONCLUSIONS

Even in long-standing T1D, IAH and defective counterregulation may be improved by a clinical strategy aimed at hypoglycemia avoidance.

Metabolic neuroimaging of the brain in diabetes mellitus and hypoglycaemia

Functional neuroimaging techniques can be used to study changes in regional brain activation, using changes in surrogate markers such as regional cerebral perfusion and rates of glucose uptake or metabolism. These approaches are shedding new light on two major health problems: the increasing burden of type 2 diabetes mellitus (T2DM), which is driven by the rising prevalence of insulin resistance and obesity; and recurrent intractable problematic hypoglycaemia, which is driven by the cognitive impairment that can occur in association with iatrogenic hypoglycaemic episodes. Some patients with diabetes mellitus lose awareness of being hypoglycaemic, which puts them at risk of severe hypoglycaemia as they are unlikely to take action to prevent the condition worsening. Involvement of corticolimbic brain and centres serving higher executive functions as well as the hypothalamus has been demonstrated in both situations and has implications for therapy. This Review describes the relevant principles of functional neuroimaging techniques and presents data supporting the notion that the dysregulation of central pathways involved in metabolic regulation, reward and appetite could contribute to problematic hypoglycaemia during therapy for diabetes mellitus and to insulin-resistant obesity and T2DM. Understanding these dysregulations could enable the development of novel clinical interventions.

[Paradoxal growth hormone and cortisol response to hypoglycemia caused by endogenous hyperinsulinemia: a case report]

Growth hormone (GH) together with cortisol are two important counter-regulatory hormones maintaining normal glycemia. Hyperinsulinemic hypoglycemia is a disorder of this counter-regulation described in neonates. We report here a rare case of reversible dissociated hypopituitarism secondary to an insulinoma in a 38-year-old man referred for investigation of hypoglycemic episodes. Hormonal investigations were in favour of dissociated anterior pituitary failure, with growth hormone and corticotroph deficiency. The hypothalamic-pituitary MRI was normal. The fasting test argued in favour of a hyperinsulinemic hypoglycemia. The abdominal scan and the endoscopic ultrasound showed a mass within the tail of the pancreas. Distal pancreatectomy was performed. Histology disclosed an insulinoma. On follow-up, no hypoglycemic episodes recurred and cortisol and GH response to induced hypoglycemia was normal. Our clinical case shows that hyperinsulinemia and hypoglycemia in patients with insulinoma can give rise to functional growth hormone and corticotrophin deficiency. The pathophysiological mechanism of this defective counter-regulation remains to be clarified; some studies suggest it could be related to hyperinsulinemia-induced decreased in CRF secretion and GHRH pulse.

Glucose counterregulatory hormones in the 72-hour fast

OBJECTIVE

To attempt to establish a reference range of glucagon concentrations during hypoglycemia.

METHODS

We measured glucagon, cortisol, and growth hormone responses in 65 patients with insulinoma and 29 normal control subjects who underwent a 72-hour fast. For comparison, we also assessed these responses in eight patients with noninsulinoma pancreatogenous hypoglycemia syndrome.

RESULTS

At the end of the fasts, median serum cortisol (19.0 mg/dL [range, 3.7 to 44.0] versus 11.0 mg/dL [range, 5.0 to 28.0], respectively; P<0.001) and growth hormone levels (3.5 ng/mL [range, 0.1 to 46.0] versus 1.2 ng/mL [range, 0.1 to 34.0], respectively; P = 0.021) were higher, whereas plasma glucagon (54.5 pg/mL [range, 11.0 to 170.0] versus 75.0 pg/mL [range, 17.0 to 940.0], respectively; P = 0.012) was lower in patients with insulinoma (serum glucose level, 39 mg/dL [range, 14 to 58]) than in control subjects (serum glucose level, 63 mg/dL [range, 47 to 89]). In contrast, the 8 patients with noninsulinoma pancreatogenous hypoglycemia syndrome, a disorder of postprandial hyperinsulinemic hypoglycemia with normal findings on a 72-hour fast (serum glucose level, 71.5 mg/dL [range, 48 to 82]), had concentrations of glucagon (81.0 pg/mL [range, 47.0 to 150.0]), cortisol (10.5 mg/dL [range, 2.7 to 17.0]), and growth hormone (1.5 ng/mL [range, 0.8 to 6.9]) similar to those in the control subjects. On multivariate analysis, the duration of the fast, baseline glucagon concentration, and male gender (but not age, body mass index, or concentrations of glucose and insulin) were correlated with end-of-fast glucagon concentration.

CONCLUSION

Defective glucagon secretion in hypoglycemic disorders applies to the stimulus of hypoglycemia but not to food deprivation. A conservative estimate for glucagon deficiency based on the minimal observed glucagon response could be a level of 10 pg/mL during hypoglycemia.

Hypoglycemia unawareness in a patient with dumping syndrome: report of a case

We report the case of a 49-yr-old man affected by coma and hypoglycemia unawareness following repetitive hypoglycemic episodes due to dumping syndrome. The dumping syndrome, which was due to partial gastrectomy and vagotomy performed for recurrent peptic ulcer, was responsible for reactive hyperinsulinemia as demonstrated by an oral glucose tolerance test. While the glucose counterregulatory hormones were all normally sensitive to specific stimulation tests, insulin-induced hypoglycemia failed to induce an adequate counterregulatory response, causing no response in plasma norepinephrine, a slight and short increase in plasma cortisol, ACTH and glucagon and an insufficient increase in plasma epinephrine and GH. This case demonstrates that hypoglycemia unawareness has to be taken into account not only in patients affected by IDDM or insulinoma but also in any case of reactive hypoglycemia.

Prevention of an increase in plasma cortisol during hypoglycemia preserves subsequent counterregulatory responses

The aim of this study was to determine whether preventing increases in plasma cortisol during antecedent hypoglycemia preserves autonomic nervous system counterregulatory responses during subsequent hypoglycemia. Experiments were carried out on 15 (8 male/7 female) healthy, overnight-fasted subjects and 8 (4 male/4 female) age- and weight-matched patients with primary adrenocortical failure. 5 d before a study, patients had their usual glucocorticoid therapy replaced with a continuous subcutaneous infusion of cortisol programmed to produce normal daily circadian levels. Both groups underwent identical 2-d experiments. On day 1, insulin was infused at a rate of 1.5 mU/kg per min, and 2-h clamped hypoglycemia (53+/-2 mg/dl) was obtained during the morning and afternoon. The next morning, subjects underwent an additional 2-h hypoglycemic (53+/-2 mg/ dl) hyperinsulinemic clamp. In controls, day 2 steady state epinephrine, norepinephrine, pancreatic polypeptide, glucagon, growth hormone, and muscle sympathetic nerve activity were significantly blunted (P < 0.01) compared with day 1 hypoglycemia. In marked contrast, when increases of plasma cortisol were prevented in the patient group, day 2 neuroendocrine, muscle sympathetic nerve activity, hypoglycemic symptoms, and metabolic counterregulatory responses were equivalent with day 1 results. We conclude that (a) prevention of increases of cortisol during antecedent hypoglycemia preserves many critical autonomic nervous system counterregulatory responses to subsequent hypoglycemia; (b) hypoglycemia-induced increases in plasma cortisol levels are a major mechanism responsible for causing subsequent hypoglycemic counterregulatory failure; and (c) our results suggest that other mechanisms, apart from cortisol, do not play a major role in causing hypoglycemia-associated autonomic failure.

Role of cortisol in the pathogenesis of deficient counterregulation after antecedent hypoglycemia in normal humans

The aim of this study was to determine the role of increased plasma cortisol levels in the pathogenesis of hypoglycemia-associated autonomic failure. Experiments were carried out on 16 lean, healthy, overnight fasted male subjects. One group (n = 8) underwent two separate, 2-d randomized experiments separated by at least 2 mo. On day 1 insulin was infused at a rate of 1.5 mU/kg per min and 2 h clamped hypoglycemia (53 +/- 2 mg/dl) or euglycemia (93 +/- 3 mg/dl) was obtained during morning and afternoon. The next morning subjects underwent a 2-h hyperinsulinemic (1.5 mU/kg per min) hypoglycemic (53 +/- 2 mg/dl) clamp study. In the other group (n = 8), day 1 consisted of morning and afternoon 2-h clamped hyperinsulinemic euglycemia with cortisol infused to stimulate levels of plasma cortisol occurring during clamped hypoglycemia (53 mg/dl). The next morning (day 2) subjects underwent a 2-h hyperinsulinemic hypoglycemic clamp identical to the first group. Despite equivalent day 2 plasma glucose and insulin levels, steady state epinephrine, norepinephrine, pancreatic polypeptide, glucagon, ACTH and muscle sympathetic nerve activity (MSNA) values were significantly (R < 0.01) blunted after day 1 cortisol infusion compared to antecedent euglycemia. Compared to day 1 cortisol, antecedent hypoglycemia produced similar blunted day 2 responses of epinephrine, norepinephrine, pancreatic polypeptide and MSNA compared to day 1 cortisol. Antecedent hypoglycemia, however, produced a more pronounced blunting of plasma glucagon, ACTH, and hepatic glucose production compared to day 1 cortisol. We conclude that in healthy overnight fasted men (a) antecedent physiologic increases of plasma cortisol can significantly blunt epinephrine, norepinephrine, glucagon, and MSNA responses to subsequent hypoglycemia and (b) these data suggest that increased plasma cortisol is the mechanism responsible for antecedent hypoglycemia causing hypoglycemia associated autonomic failure.

Surgical removal of insulinoma restores glucose recovery from hypoglycaemia but does not normalize insulin action

In the present study we have evaluated the effects of chronic hyperinsulinaemia secondary to insulinoma, on insulin sensitivity and on counter-regulatory responses to hypoglycaemia. We studied six patients (M/F = 3/3; age = 40 +/- years), before and 6-9 months after surgical ablation of the neoplasia, by means of an euglycaemic-hyperinsulinaemic clamp (1 mU kg-1 min-1). Seven normal subjects (M/F = 4/3; age = 38 +/- 6 years) underwent the same experimental study as the control subjects. In insulinoma patients after 100 min of the euglycaemic-hyperinsulinaemic clamp, glycaemia was allowed to drop to a minimum value of 1.9 mmol L-1, and recovery evaluated after interrupting insulin infusion. During the entire study, 3-3H-glucose was infused to determine hepatic glucose production and glucose utilization. Surgical removal of the pancreatic adenoma was followed by a reduction in body weight (BMI = 25.7 +/- 1.9 vs. 23.0 +/- 1.6 kg m-2; P < 0.05), normalization of fasting plasma levels of glucose (2.94 +/- 0.16 vs. 4.83 +/- 0.11 mmol L-1), insulin (162 +/- 24 vs. 48 +/- 12 pmol L-1) and of basal hepatic glucose production (7.6 +/- 0.7 vs. 12.2 +/- 1.11 mumol kg-1 min-1). Before the operation, insulin-mediated glucose disposal was significantly lower than in the controls (30.8 +/- 3.1 vs. 49.1 +/- 3.1 mumol kg-1 min-1). Six to nine months after surgical removal of the adenoma, glucose utilization was unchanged (30.5 +/- 3.3 mumol kg-1 min-1) and still significantly lower than in controls (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term recovery from unawareness, deficient counterregulation and lack of cognitive dysfunction during hypoglycaemia, following institution of rational, intensive insulin therapy in IDDM

Hypoglycaemia unawareness, is a major risk factor for severe hypoglycaemia and a contraindication to the therapeutic goal of near-normoglycaemia in IDDM. We tested two hypotheses, first, that hypoglycaemia unawareness is reversible as long as hypoglycaemia is meticulously prevented by careful intensive insulin therapy in patients with short and long IDDM duration, and that such a result can be maintained long-term. Second, that intensive insulin therapy which strictly prevents hypoglycaemia, can maintain long-term near-normoglycaemia. We studied 21 IDDM patients with hypoglycaemia unawareness and frequent mild/severe hypoglycaemia episodes while on "conventional" insulin therapy, and 20 nondiabetic control subjects. Neuroendocrine and symptom responses, and deterioration in cognitive function were assessed in a stepped hypoglycaemia clamp before, and again after 2 weeks, 3 months and 1 year of either intensive insulin therapy which meticulously prevented hypoglycaemia (based on physiologic insulin replacement and continuous education, experimental group, EXP, n = 16), or maintenance of the original "conventional" therapy (control group, CON, n = 5). At entry to the study, all 21 IDDM-patients had subnormal neuroendocrine and symptom responses, and less deterioration of cognitive function during hypoglycaemia. After intensive insulin therapy in EXP, the frequency of hypoglycaemia decreased from 0.5 +/- 0.05 to 0.045 +/- 0.02 episodes/patient-day; HbA1c increased from 5.83 +/- 0.18 to 6.94 +/- 0.13% (range in non-diabetic subjects 3.8-5.5%) over a 1-year period; all counterregulatory hormone and symptom responses to hypoglycaemia improved between 2 weeks and 3 months with the exception of glucagon which improved at 1 year; and cognitive function deteriorated further as early as 2 weeks (p < 0.05). The improvement in responses was maintained at 1 year. The improvement in plasma adrenaline and symptom responses inversely correlated with IDDM duration. In contrast, in CON, neither frequency of hypoglycaemia, nor neuroendocrine responses to hypoglycaemia improved. Thus, meticulous prevention of hypoglycaemia by intensive insulin therapy reverses hypoglycaemia unawareness even in patients with long-term IDDM, and is compatible with long-term near-normoglycaemia. Because carefully conducted intensive insulin therapy reduces, not increases the frequency of moderate/severe hypoglycaemia, intensive insulin therapy should be extended to the majority of IDDM patients in whom it is desirable to prevent/delay the onset/progression of microvascular complications.

Recovery of epinephrine response but not hypoglycemic symptom threshold after intensive therapy in type 1 diabetes

PURPOSE

Patients with intensively treated insulin-dependent diabetes mellitus (IDDM) exhibit more severe defects in counterregulatory hormone secretion and symptom recognition during hypoglycemia than do conventionally treated patients. In this prospective study in patients with preexisting defects in counterregulation, we examined the induction and reversibility of impaired symptomatic and adrenomedullary responses to hypoglycemia in 5 patients with IDDM (diabetes duration of 2 to 16 years; aged 19 to 36 years; 3 women, 2 men) who were receiving intensive therapy.

METHODS

Counterregulatory responses were assessed by using a single-step (approximately 2.8 mmol/L plasma glucose) and multiple-step (from approximately 5 mmol/L to 2.2 mmol/L plasma glucose) clamped hypoglycemia procedure. Patients were first studied after a stable period of conventional insulin therapy (glycosylated hemoglobin [HbA1c] 9.5 +/- 1.2%), then after 3 to 5 months of intensive therapy (HbA1c 6.6 +/- 0.2%), and a third time after resuming conventional therapy (HbA1c 8.7 +/- 0.9%).

RESULTS

Intensive therapy was associated with a 44% decline (P < 0.01) in the average plasma epinephrine increase during hypoglycemia, and the plasma glucose level required to stimulate epinephrine secretion fell from 3.7 +/- 0.2 to 3.0 +/- 0.1 mmol/L (P < 0.01). The threshold, but not the magnitude, of the plasma norepinephrine response was similarly altered. Hypoglycemic symptoms also decreased in intensity (by 67%, P < 0.01), and the glucose level required for symptom activation fell from 3.4 +/- 0.3 to 2.7 +/- 0.2 mmol/L, P < 0.01). When conventional therapy was resumed, the abnormalities in the epinephrine response due to intensive therapy were almost completely reversed. However, the reduction in symptoms and the altered thresholds for plasma norepinephrine were not reversed.

CONCLUSIONS

There is dissociation between the treatment-associated defects in hypoglycemia counterregulation in IDDM, and an increase in average glycemia produced by a return to conventional insulin therapy is not sufficient to reverse hypoglycemia unawareness worsened by intensive therapy.

Restoration of hypoglycaemia awareness in patients with long-duration insulin-dependent diabetes

Hypoglycaemia without warning is a dangerous complication of insulin-dependent diabetes mellitus and it limits the use of intensified insulin therapy to reduce chronic diabetic complications. To investigate the possibility of restoring awareness; symptomatic, cognitive, and hormonal responses to controlled hypoglycaemia were studied in insulin-dependent diabetic patients with long disease duration (6 with good glycaemic control and 6 with poor control) before and after hypoglycaemia avoidance. At the start of the study, all had loss of hypoglycaemia awareness. Responses to the initial challenge were small (pooled area under curve [AUC] adrenaline 5.75 [SE 0.07] nmol/L per 260 min, pooled AUC symptom score 80 [1.3]) and only started when plasma glucose was significantly lower than the 2.8 (0.1) mmol/L at which cognitive function deteriorated. After 4.1 (1.1) months' scrupulous hypoglycaemia avoidance, hormone and symptom responses to the challenge were increased (AUC adrenaline 15.9 [0.1] nmol/L per 260 min, p = 0.01; AUC symptom score 275 [7], p < 0.001), starting at plasma glucose concentrations significantly higher than that causing cognitive dysfunction. Glycosylated haemoglobin did not deteriorate significantly. We conclude that the normal hierarchy of subjective awareness before cognitive dysfunction during hypoglycaemia can be restored by avoiding hypoglycaemia. This is independent of disease duration or initial metabolic control.

Reversibility of unawareness of hypoglycemia in patients with insulinomas

BACKGROUND

A lack of appropriate autonomic warning symptoms before the development of neuroglycopenia occurs frequently in patients with diabetes mellitus. The pathogenesis of this phenomenon is unclear, but it is associated with intensive insulin therapy, prolonged duration of diabetes, frequent episodes of hypoglycemia, and impaired glucose counterregulation. Recently, it has been proposed that repeated episodes of hypoglycemia may themselves induce the phenomenon.

METHODS

To test this hypothesis and to determine whether the phenomenon is reversible, we assessed autonomic and neuroglycopenic symptoms, counterregulatory hormonal responses, and cognitive function during stepped hypoglycemic-clamp studies in 6 patients with insulinomas before and approximately six months after curative surgery and in 14 normal subjects matched for age, weight, and sex.

RESULTS

Before surgery, the patients with insulinomas had lower scores than the normal subjects for autonomic symptoms (mean [+/- SD], 3.5 +/- 0.8 vs. 9.6 +/- 4.5) and neuroglycopenic symptoms (2.8 +/- 1.5 vs. 8.9 +/- 5.3). The patients also had impaired counterregulatory hormonal responses (their plasma epinephrine, norepinephrine, glucagon, growth hormone, and cortisol responses before surgery were 187 +/- 227 pg per milliliter [1.03 +/- 1.25 nmol per liter], 223 +/- 85 pg per milliliter [1.32 +/- 0.50 nmol per liter], 86 +/- 21 ng per liter, 7.4 +/- 5.2 micrograms per liter, and 12.1 +/- 1.5 micrograms per deciliter [334 +/- 41 nmol per liter], respectively, as compared with 842 +/- 439 pg per milliliter [4.63 +/- 2.41 nmol per liter], 519 +/- 150 pg per milliliter [3.07 +/- 0.89 nmol per liter], 201 +/- 58 ng per liter, 25.3 +/- 13.7 micrograms per liter, and 26.3 +/- 1.2 micrograms per deciliter [726 +/- 33 nmol per liter] in the normal subjects) and less deterioration in cognitive function than the normal subjects during hypoglycemia (sum of z scores for seven tests of cognitive function, 1.7 +/- 1.9 vs. 8.9 +/- 3.5) (P < 0.02 for all comparisons). Surgical cure reversed all these abnormalities (P not significant for all comparisons with the normal subjects).

CONCLUSIONS

Hypoglycemia itself can induce unawareness of the autonomic and neuroglycopenic symptoms of hypoglycemia and decrease the counterregulatory hormonal responses to hypoglycemia.

Gender differences in counterregulation to hypoglycaemia

To investigate the effect of gender on catecholamine responses to hypoglycaemia, single-step euglycaemic-hypoglycaemic clamps have been performed in 14 healthy men and 17 women. Adrenaline responses were 44% lower in females (p < 0.01) and noradrenaline 17% lower (p = 0.08). In response to low-dose intravenous insulin infusion (0.3 mU.kg-1.min-1), plasma glucose fall and counterregulation in seven men and seven women had a different course (p < 0.001), with different glucose kinetics. In men, endogenous glucose output recovered quickly to levels that exceeded basal; in women suppression of endogenous glucose output was more prolonged, without rates ever exceeding basal (p < 0.05). Peripheral glucose uptake was stimulated in men only. The hormones of acute glucose counterregulation (catecholamines and glucagon) did not differ between the sexes during this challenge, the catecholamine response in the women being supported by the continuous fall in plasma glucose. These results suggest that: 1) catecholamine responses to moderately controlled hypoglycaemia are diminished in women, and 2) peripheral insulin sensitivity in men is enhanced over that of women but hepatic sensitivity to insulin may be greater in women.

Pre- and postoperative glucose levels for eliciting hypoglycaemic responses in a patient with insulinoma

Counterregulatory hormones and hypoglycaemic symptoms were studied during a gradual decline in plasma glucose in a 66-year-old man before and 9 weeks after removal of an insulin-producing tumour. Before surgery the adrenaline started to respond first at plasma glucose 2.8 mmol l-1. He reported no autonomic symptoms although plasma glucose fell to 2.3 mmol l-1 with a corresponding adrenaline rise to 4.64 nmol l-1. After surgery adrenaline responded at a plasma glucose of 3.7 mmol l-1 and he started to sweat and tremble at a plasma glucose of 3.1 mmol l-1 (corresponding adrenaline 2.63 nmol l-1). The lack of autonomic symptoms preoperatively may indicate adrenaline insensitivity, possibly as a result of repeated hypoglycaemia.