Insulinoma: how reliable is the biochemical evidence?

BACKGROUND AND METHODS: We report a case of insulinoma in which the diagnosis was very challenging as some of the biochemical data were consistently equivocal. In order to assess the relative reliability of the analytical tests, retrospective biochemical data on 45 other cases of histologically confirmed insulinoma were evaluated, enabling the most secure diagnostic process to be identified. RESULTS: The data showed that insulin concentrations alone, although measurable, were equivocal in 17% of cases. The addition of C-peptide values clarified the diagnosis in about 50% of the borderline cases, whilst ketone (beta-hydroxybutyrate) concentrations were low during the prevailing hypoglycaemia in all cases. CONCLUSION: The combination of these three tests is suggested as the most effective method for the biochemical diagnosis of hypoglycaemia due to insulinoma.

Progression of diabetic nephropathy--is diurnal blood pressure rhythm as important as absolute blood pressure level?

BACKGROUND: Hypertensive non-diabetic patients who lack the normal nocturnal decline in blood pressure ('non-dippers') have an increased incidence of cardiovascular complications. Poor blood pressure control is known to exacerbate the decline in glomerular filtration rate in patients with diabetic nephropathy. METHODS: The aim of this study was to assess the contribution of abnormal blood pressure diurnal rhythm to the progression of diabetic nephropathy. We retrospectively studied 26 diabetic patients with hypertension, proteinuria and relentless progressive impairment of renal function due to diabetic nephropathy between 1990 and 1996. Patients underwent ambulatory blood pressure monitoring and were classified as either 'dippers' or 'non-dippers' according to their blood pressure diurnal rhythm. Dippers were patients whose mean sleeping blood pressure (both systolic and diastolic) was 10% less than blood pressure whilst awake. Weight, glycated haemoglobin, serum creatinine (micromol/l) and blood pressure (mmHg) were recorded on a 3-monthly basis. Twenty four hour urine protein excretion and creatinine clearance were recorded annually. The rate of decline of creatinine clearance was derived from serum creatinine estimation. RESULTS: In the 'dipper' group, the rate of decline of creatinine clearance was -2.9 ml/min/year and in those with abnormal blood pressure diurnal rhythm it was -7.9 ml/min/year (P<0.05). There was no significant difference in day-time mean blood pressures, glycated haemoglobin, age and numbers with insulin-dependent diabetes mellitus. CONCLUSION: We found that there was a profound effect of non-dipping upon the rate of decline of renal function in patients with diabetic nephropathy.

Two aberrant splicings caused by mutations in the insulin receptor gene in cultured lymphocytes from a patient with Rabson-Mendenhall's syndrome.

Rabson-Mendenhall's syndrome is one of the most severe forms of insulin resistance syndrome. We analyzed an English patient described elsewhere and found novel mutations in both alleles of the insulin receptor gene. One is a substitution of G for A at the 3' splice acceptor site of intron 4, and the other is an eight-base pair deletion in exon 12. Both decrease mRNA expression in a cis-dominant manner, and are predicted to produce severely truncated proteins. Surprisingly, nearly normal insulin receptor levels were expressed in the patient's lymphocytes, although the level of expression assessed by immunoblot was approximately 10% of the control cells. Insulin binding affinity was markedly reduced, but insulin-dependent tyrosine kinase activity was present. Analyzing the insulin receptor mRNA of the patient's lymphocytes by reverse transcription PCR, we discovered aberrant splicing caused by activation of a cryptic splice site in exon 5, resulting in a four-amino acid deletion and one amino acid substitution, but restoring an open reading frame. Skipped exon 5, another aberrant splicing, was found in both the patient and the mother who had the heterozygotic mutation, whereas activation of the cryptic splice site occurred almost exclusively in the patient. Transfectional analysis in COS cells revealed that the mutant receptor produced by cryptic site activation has the same characteristics as those expressed in patient's lymphocytes. We speculate that this mutant receptor may be involved in the relatively long survival of the patient by rescuing otherwise more severe phenotypes resulting from the complete lack of functional insulin receptors.

Gene expression and serum levels of insulin-like growth factors (IGFs) and IGF-binding proteins in a case of non-islet cell tumour hypoglycaemia.

We describe a case of non-islet cell tumour hypoglycaemia (NICTH) associated with a renal cell carcinoma. Serum insulin-like growth factors (IGFs) (including IGF-II E peptide), IGF-binding proteins (IGFBPs), insulin and C-peptide were measured before and after surgical removal of the tumour. IGFBPs were visualized by Western ligand blotting. Preoperatively 'big' IGF-II and IGFBP-2 levels were raised. IGF-I, IGFBP-1 and IGFBP-3 were low, while insulin, C-peptide and GH were undetectable. These changes were reversed by 2 days postoperatively. Protease assays showed little IGFBP-3 protease activity preoperatively. Preoperatively, neutral chromatography demonstrated most of the immunoassayable IGFBP-3 in a high molecular weight form with a small amount of IGF-II. Most of the IGF-II and big IGF-II eluted in lower molecular weight forms. Postoperative samples showed a shift in IGF-II which became increasingly associated with IGFBP-3 in both low and high molecular weight complexes. By Northern blotting, expression of all species of IGF-II mRNA in the tumour was 10-fold greater than in normal human liver. The tumour did not express IGFBP-1 or IGFBP-2. IGFBP-3 was expressed in small amounts, while the expression of IGFBP-4 was two-fold higher than in liver. In conclusion, we have confirmed high levels of big IGF-II and IGFBP-2 in NICTH, changes which are reversed postoperatively. The IGF-II is derived from the tumour which overexpresses these genes but IGFBP-2 probably arises from extratumour upregulation.

Four mutant alleles of the insulin receptor gene associated with genetic syndromes of extreme insulin resistance.

We identified four novel mutant alleles of the insulin receptor gene in three patients with genetic syndromes associated with insulin resistance. Two mutant alleles of the insulin receptor gene were identified in a patient with the Rabson-Mendenhall syndrome who was a compound heterozygote for a mutation at the 3'-splice acceptor site of intron 4 (AG-->GG), the first mutation causing an aberrant splicing at this locus, and a deletion of eight base pairs in exon 12. The second patient with leprechaunism was also a compound heterozygote for a deletion of one base pair in exon 19 and a mutation, Thr910-->Met, which causes impaired receptor processing. Interestingly, the third patient with type A syndrome was a simple heterozygote for the identical one base pair deletion. The fact that the same one base pair deletion links to type A in a simple heterozygote and to leprechaunism in a compound heterozygote appears consistent with the hypothesis that the severity of mutations will determine the phenotype.

Remission of non-insulin-dependent diabetes mellitus following resection of a parathyroid adenoma.

A 56-year-old woman presented with diabetes mellitus and primary hyperparathyroidism simultaneously. Initial random blood glucose was recorded at 20.8 mmol l-1, serum calcium was 3.07 mmol l-1 (normal range 2.10-2.55 mmol l-1), and plasma parathyroid hormone estimation by intact assay was 110 ng l-1 (normal range 10-65 ng l-1). Initial glycated haemoglobin was 9.4% (non-diabetic range < 7.5%). Left lower parathyroidectomy was carried out and pathology confirmed the presence of a chief cell adenoma. The gland measured 10 x 5 x 5 mm. Following parathyroidectomy serum calcium normalized, glucose tolerance improved, and a subsequent 75 g oral glucose tolerance test was normal. The patient weighted 80 kg at presentation but the post-operative weight had risen to 81.5 kg. The most recent glycated haemoglobin was 4.6%. Primary hyperparathyroidism may have a reversible effect on glucose tolerance.

Severe ketoacidosis complicated by 'ecstasy' ingestion and prolonged exercise.

Ecstasy (3,4-methylenedioxymethamphetamine or MDMA) is used with increasing frequency as a recreational drug. Accumulated evidence over recent years indicates a growing demand for the drug with a corresponding increase in number of reports of adverse effects from its use. There are reported metabolic disturbances due to MDMA use. These, in addition to the prolonged exercise involved in dancing at 'raves' where MDMA may be used, may exacerbate ketoacidosis. We report two cases of ketoacidosis complicated by MDMA ingestion.

Glomerular charge selectivity in type 1 (insulin-dependent) diabetes mellitus.

Glomerular charge selectivity was assessed using the ratio of the clearance of pancreatic isoamylase to the clearance of the more anionic salivary isoamylase (CPAm/CSAm) in 12 normal subjects and 50 patients with Type 1 diabetes: 13 with normal albumin excretion and short duration of diabetes (< 5 years), 15 with normal albumin excretion and long duration of diabetes (> 15 years), 13 with microalbuminuria, and 9 with clinical nephropathy. None had serum creatinine > 200 mumol l-1. There were no significant differences in CPAm/CSAm between the normal subjects and the two groups of normoalbuminuric patients with Type 1 diabetes. CPAm/CSAm was significantly lower in diabetic patients with microalbuminuria or clinical nephropathy than in normoalbuminuric patients with Type 1 diabetes. When the 37 patients with normoalbuminuria and long-standing diabetes, microalbuminuria, and nephropathy were considered together, there was a significant negative correlation between CPAm/CSAm and albumin excretion rate (rs = 0.71, p < 0.001). Progressive impairment of glomerular charge selectivity at the molecular size of amylase (molecular mass 56 kDa) accompanies increasing albuminuria in Type 1 diabetes.

Blood rheology and albumin excretion in diabetic pregnancy.

Blood rheology is altered in diabetes and also in non-diabetic pregnant women. The cumulative effect of hyperfiltration, abnormal rheology of pregnancy, and diabetes could be one mechanism contributing to increased intraglomerular pressure and albuminuria in diabetic pregnancy. We conducted a prospective study of 22 Type 1 (insulin-dependent) diabetic patients and 22 non-diabetic women to determine if there was an association of altered blood rheology on glomerular function in diabetic pregnancy. Albumin excretion showed no increment with increasing gestation and was similar in diabetic and non-diabetic women throughout pregnancy (first trimester: 5.0 (3.0-14.0) vs 5.8 (3.7-10.7) mg l-1, p = 0.89; second trimester: 6.0 (5.0-12.0) vs 5.1 (3.6-10.4) mg l-1, p = 0.25; third trimester: 7.5 (3.5-16.0) vs 4.9 (2.9-7.3) mg l-1, p = 0.18). Red cell aggregation index increased in both groups between the first and third trimesters (diabetic patients: mean difference 2.0; Cl: 1.0-2.9, p = 0.003, and control patients: mean difference 2.3, Cl: 1.0-3.5, p = 0.002). Fibrinogen levels were significantly higher between the third and first trimesters in diabetic patients (mean difference 0.7, Cl: 0.2-1.3 g l-1, p = 0.006). Pregnancy, therefore, was associated with increased red cell aggregation, related in part to increased fibrinogen levels but the extent of change was similar in diabetic and nondiabetic women and appeared to have no adverse effect on glomerular function in pregnant insulin-dependent diabetic women.

Reversible effects of cessation and recommencement of thyroxine treatment on insulin-like growth factors (IGFs) and IGF-binding proteins in patients with total thyroidectomy.

There is a complex relationship between the thyroid and pituitary GH/insulin-like growth factor (IGF) axes. IGFs circulate in association with six specific high affinity binding proteins (IGFBPs) that modulate their bioactivity and bioavailability. Recent evidence suggests that gene expression and circulating levels of IGFBPs are related to prevailing thyroid hormone status. We have investigated the effects of both withdrawal and reinstitution of thyroid hormone replacement on circulating IGF and IGFBP levels in athyreotic patients (n = 10). The mean IGF-I concentration fell from a basal level of 191.8 +/- 12 micrograms/L to a nadir of 136.4 +/- 17.8 micrograms/L (P = 0.026) 5 weeks after stopping T4 treatment and returned to normal values 3 weeks after recommencement of replacement treatment. The fall in IGF-II levels followed a similar pattern from a basal mean level of 649 +/- 33.7 to 547 +/- 42.7 micrograms/L (P = 0.026) at 5 weeks. These changes paralleled the fall in free T3 and free T4. Similarly, IGFBP-1 levels fell after stopping T4 treatment from a basal level of 54.8 +/- 4.0 to 24.6 +/- 7.0 micrograms/L (P = 0.001) 5 weeks later. After T4 treatment was restarted, IGFBP-1 levels rose and were not significantly different from basal values by week 8. There were strong positive correlations between paired data sets for IGFBP-1 and free T3 (r = 0.488; P = 0/0037) and free T4 (r = 0.56; P = 0.0006), and a strong negative correlation with TSH (r = -0.515; P = 0.0001). Insulin is known to be important in the regulation of IGFBP-1, but no changes in fasting insulin levels during T4 withdrawal were noted, and levels of IGFBP-1 did not exhibit the normal inverse relationship with circulating insulin levels. Levels of IGFBP-2, assessed by Western ligand blotting, increased during the development of hypothyroidism, peaked 5 weeks after stopping T4 replacement, and declined on reinstitution of replacement treatment. A further level of regulation of the IGF-IGFBP axis is afforded by the presence of specific circulating IGFBP proteases. Proteases directed against IGFBP-3 proteolytically cleave the major carrier BP in the circulation and reduce its binding affinity, possibly resulting in increased tissue IGF bioavailability. Despite the marked reduction in circulating IGF levels and the generation of significant biochemical hypothyroidism, IGFBP-3 protease activity was not apparent during the 10-week period of the study.(ABSTRACT TRUNCATED AT 400 WORDS)

Glomerular charge selectivity in primary glomerulopathies.

1. Glomerular charge selectivity was assessed using the ratio of the clearance of pancreatic isoamylase to the clearance of the more anionic salivary isoamylase (CPAm/CSAm) in 53 patients with primary glomerulopathies (minimal change nephropathy, idiopathic membranous nephropathy, IgA nephropathy) and a wide range of albumin excretion rates and in 31 healthy subjects. Fractional clearances of pancreatic and salivary isoamylases (FCPAm, FCSAm) and of albumin (FCAlb) were also measured. 2. CPAm/CSAm and FCPAm were negatively correlated with FCAlb for the whole patient group (rs = -0.56 and rs = -0.65, respectively, P < 0.0001 for both), but there was no correlation of FCSAm with FCAlb. 3. For patients with near-normal albumin excretion rates (< 100 mg/24 h), there was no difference in CPAm/CSAm between the three types of glomerulopathy or between patients and healthy subjects. 4. These data suggest that glomerular charge selectivity at the size of amylase (which is smaller than albumin) is progressively lost as albuminuria increases from normal to the nephrotic range. Size restriction progressively increases until albuminuria is very heavy. When the albumin excretion rate is near normal, charge selectivity is also normal in the three main forms of primary glomerulopathy.

Insulin-like growth factor binding protein 1 response to acute insulin induced hypoglycaemia in type 1 diabetes.

OBJECTIVES: Insulin is believed to be the prime regulator of insulin-like growth factor binding protein 1 (IGFBP-1) secretion, and in normal subjects acute insulin induced hypoglycaemia exerts a rapid effect on concentrations of IGFBP-1, and may also influence insulin-like growth factor I (IGF-I) concentrations. The rise in IGFBP-1 concentrations in normal subjects following hypoglycaemia has been suggested to be due to suppression of endogenous insulin secretion. We have examined this further by studying diabetics with no endogenous insulin secretion. DESIGN: We have compared the IGFBP-1 response to acute insulin induced hypoglycaemia in normal subjects and patients with Type 1 (insulin dependent) diabetes mellitus. METHODS: Insulin tolerance tests were performed using a bolus of insulin (0.15 U/kg), in six control subjects and six patients with Type 1 diabetes. MEASUREMENTS: Serum levels of IGFBP-1, insulin, glucose, and IGF-I were measured at regular intervals during the insulin tolerance test. RESULTS: Blood glucose fell to a nadir which coincided with the onset of the acute autonomic reaction 'R' in both groups. The basal concentration of IGF-I was significantly lower in the diabetic group at 0.4 +/- 0.1 kU/l, compared to 0.9 +/- 0.1 kU/l in the control group, but there was no significant change in IGF-I concentrations in response to hypoglycaemia in either group. Hypoglycaemia provoked a fall in IGFBP-1 in patients with Type 1 diabetes, from 38 +/- 9 micrograms/l basally to 17 +/- 3 micrograms/l at R + 120 minutes, with a return to basal values of 45 +/- 11 micrograms/l at R + 180 minutes. In the control subjects there was no fall in IGFBP-1, but a significant increase to 71 +/- 14 micrograms/l at R + 180 minutes. CONCLUSION: This difference in the IGFBP-1 response in the presence of a similar glucose response suggests that in Type 1 diabetes there may be different sensitivities to the actions of exogenous insulin on IGFBP-1 regulation.

The effect of recombinant insulin-like growth factor I on ketone body, lipid and apolipoprotein concentrations and its use to treat ketoacidosis in severe insulin resistance.

The effect of recombinant insulin-like growth factor I (rhIGF-I) on ketone body concentrations was studied in a patient with the Mendenhall syndrome, a rare insulin-resistant state. Treatment with intravenous rhlGF-I for an episode of ketoacidosis led to a clinical and biochemical improvement. One month later, the effect of 20 mg rhlGF-I infused daily for 4 days on ketone body concentrations was studied. From peak concentrations 24 h prior to the study to a nadir 72 h after the infusion commenced, acetoacetate fell from 4.17 mmol l-1 to 0.86 mmol l-1, beta-hydroxybutyrate from 9.91 mmol l-1 to 2.03 mmol l-1, and acetone from 2 mmol l-1 to 0.4 mmol l-1. Further studies of rhlGF-1 use caused a fall in concentrations of cholesterol, triglyceride, VLDL, LDL, and apolipoprotein B. Infusion of rhlGF-1 reduces ketone body concentrations and may be life-saving in the treatment of ketoacidosis developing in a patient with a severe insulin-resistant state.

Hypothyroidism presenting with cardiac tamponade.

Two cases of cardiac tamponade initially suspected to be secondary to malignancy are presented. Primary hypothyroidism can cause pericardial effusions and thyroid function tests confirmed this diagnosis in these cases. Hypothyroidism should be considered as an underlying cause of pericardial effusion in cardiac tamponade.

Response of insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1) and IGFBP-3 to IGF-I treatment in severe insulin resistance.

It has been suggested that recombinant human IGF-I (rhIGF-I) is a potential therapeutic agent in diabetes mellitus. It is known to have glucose-lowering effects in normal individuals, in patients with non-insulin-dependent diabetes (NIDDM) and in extreme insulin-resistant states. IGF-binding proteins (IGFBPs) have the potential to affect the biological activity of rhIGF-I. We have studied the effect of infused rhIGF-I on IGFBP-1 and IGFBP-3 in a patient with Mendenhall's syndrome, a rare insulin-resistant state. During an infusion of 20 mg rhIGF-I, glucose concentrations fell from 44.1 +/- 7.2 to 31.5 +/- 7.2 (S.E.M.) mmol/l (P = 0.001), and insulin and C-peptide levels fell from 920 +/- 62 to 542 +/- 45 mU/l (P = 0.008) and 5466 +/- 633 to 3071 +/- 297 pmol/l (P = 0.02) respectively. Significant lowering of phosphate, magnesium and alkaline phosphatase concentrations was also noted. IGF-I levels rose from 48 +/- 10.2 to 410 +/- 50.1 micrograms/l (P = 0.001), and those of IGF-II fell from 279.8 +/- 8.3 to 104.3 +/- 7.9 micrograms/l (P = 0.001). IGFBP-1 concentrations did not significantly change during the infusion but those of IGFBP-3 increased from 1655 +/- 127 to 2197 +/- 334 micrograms/l (P = 0.002), despite a significant fall in GH concentrations from 10.7 +/- 2.6 to 4.1 +/- 1.1 mU/l (P = 0.007), suggesting that IGFBP-3 regulation is also IGF-I-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of glomerular charge selectivity in man by differential clearance of isoamylases.

1. Glomerular charge selectivity was assessed using the ratio of the clearance of pancreatic isoamylase to the clearance of the more anionic salivary isoamylase (CPAm/CSAm) in 30 normal subjects, 14 patients with minimal proteinuria and 23 patients with heavy proteinuria due to primary glomerulopathies. Seven patients with minimal change nephropathy were studied in relapse and remission. 2. CPAm/CSAm exceeded 2.0 (range 2.1-6.1) in all normal subjects, indicating that the normal glomerular capillary wall possesses charge selectivity at the molecular size of amylase (molecular mass 56 kDa). 3. CPAm/CSAm was significantly lower in patients with heavy proteinuria than in normal subjects or patients with minimal proteinuria. CPAm/CSAm was low in patients with minimal change nephropathy in relapse and rose into the normal range with steroid-induced remission. 4. These data suggest that heavy proteinuria in primary glomerulopathies is accompanied by loss of glomerular charge selectivity. Remission of minimal change nephropathy is associated with restoration of normal charge selectivity.

An evaluation of bone density and turnover in premenopausal women with type 1 diabetes mellitus.

Measurement of bone density and turnover was assessed in 20 premenopausal females with Type 1 diabetes mellitus and 27 age-sex-matched controls. Measurement was made of spinal (L2-4) and neck of femur bone density by dual-energy X-ray absorptiometry. L2-4 density was significantly higher in the diabetic patients compared with controls (1.224 +/- 0.021 g cm-2 vs. 1.161 +/- 0.020 g cm-2: p = 0.016). No significant difference was noted between the groups in neck of femur density. Measurement of bone formation was assessed by serum alkaline phosphatase and bone resorption by fasting urinary hydroxyproline/creatinine ratio. Alkaline phosphatase was significantly higher in the diabetic patients (185 +/- 16 Ul-1 vs 135 +/- 10 Ul-1: p < 0.01) as was hydroxyproline/creatinine ratio (0.028 +/- 0.003 vs 0.017 +/- 0.002: p = 0.002). No significant correlation was found between L2-4 density and glycated haemoglobin, duration of diabetes or daily dose of insulin taken. These data suggest that osteopenia is not associated with Type 1 diabetes mellitus; however these patients do have evidence of increased bone turnover and may therefore be at risk of osteoporosis in later life, particularly after the menopause.

Thyroid abscess complicating subacute thyroiditis: a consequence of steroid therapy?

A patient with subacute thyroiditis developed a thyroid abscess after drainage of a pilonidal abscess. An infective focus in a patient with subacute thyroiditis on steroids should be treated aggressively with adequate antibiotic cover.