Autoimmune insulin syndrome

Scientific opinion on the relationship between intake of alpha-lipoic acid (thioctic acid) and the risk of insulin autoimmune syndrome

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on the relationship between alpha-lipoic acid (ALA) and the risk of insulin autoimmune syndrome (IAS). The Panel was also asked to advise on the dose below which ALA added to foods is not expected to cause IAS. A review of all possible adverse effects associated with consumption of ALA was not requested. This mandate refers to the procedure under Article 8(2) of Regulation (EC) No 1925/2006 on addition of vitamins, minerals and certain other substances to foods. No pre-established rule exists for the evaluation of the safety of foods when classical toxicity tests cannot be used, e.g. for autoimmune diseases. Published scientific evidence was retrieved through comprehensive literature searches, particularly 49 case reports in which IAS developed following ALA consumption. In all cases, IAS resolved after a few weeks to months when ALA was discontinued. No publication linking the intake of ALA naturally occurring in foods to IAS was identified. The Panel concludes that the consumption of ALA added to foods, including food supplements, is likely to increase the risk of developing IAS in individuals with certain genetic polymorphisms, who cannot be readily identified without genetic testing. The plausible mechanism of such an effect has not yet been fully elucidated. The incidence of IAS in Europe is low and likely lower than in Japan where it has been estimated to be 0.017 per 100,000 inhabitants in 2017-2018. Considering the limited data available, the risk associated with the development of IAS following ALA consumption cannot be quantified precisely. An ALA dose below which IAS is not expected to occur is likely to vary between individuals and cannot be determined from the available data.

Clinical and Laboratory Aspects of Insulin Autoantibody-Mediated Glycaemic Dysregulation and Hyperinsulinaemic Hypoglycaemia: Insulin Autoimmune Syndrome and Exogenous Insulin Antibody Syndrome

Autoimmune glycaemic dysregulation and hyperinsulinaemic hypoglycaemia mediated by insulin autoantibodies is an increasingly recognised but controversial phenomenon described in both exogenous insulin naïve (insulin autoimmune syndrome) and exposed (exogenous insulin antibody syndrome) individuals. There has been a significant proliferation of case reports, clinical studies and reviews in the medical literature in recent years which have collectively highlighted the discrepancy between experts in the field with regard to the nomenclature, definition, proposed pathophysiology, as well as the clinical and biochemical diagnostic criteria associated with the condition. The essential characteristics of the condition are glycaemic dysregulation manifesting as episodes of hyperglycaemia and unpredictable hyperinsulinaemic hypoglycaemia associated with high titres of endogenous antibodies to insulin. Although the hypoglycaemia is often life-threatening and initiation of targeted therapies critical, the diagnosis is often delayed and attributable to various factors including: the fact that existence of the condition is not universally accepted; the need to exclude surreptitious causes of hypoglycaemia; the diverse and often complex nature of the glycaemic dysregulation; and the challenge of diagnostic confirmation. Once confirmed, the available therapeutic options are expansive and the reported responses to these therapies have been variable. This review will focus on our evolving understanding, and the associated diagnostic challenges - both clinical and laboratory - of this complex condition.

Ligand-binding characteristics of feline insulin-binding immunoglobulin G

Polyclonal immunoglobulin (Ig) G autoantibodies against insulin have been identified in sera of healthy cats. We purified and fractionated insulin-binding IgGs from cat sera by affinity chromatography and analyzed affinity of insulin-binding IgGs for insulin and their epitopes. Following the passing of fraction A, which did not bind to insulin, insulin-binding IgGs were eluted into two fractions, B and C, by affinity chromatography using a column fixed with bovine insulin. Dissociation constant (KD) values between insulin-binding IgGs and insulin, determined by surface plasmon resonance analysis (Biacore™system), were 1.64e⁻⁴ M for fraction B (low affinity IgGs) and 2e⁻⁵ M for fraction C (high affinity IgGs). Epitope analysis was conducted using 16 peptide fragments synthesized in concord with the amino acid sequence of feline insulin by an enzyme-linked immunosorbent assay. Fractions B and C showed higher absorbance (affinity) of the peptide fragment of 10 amino acid residues at the carboxyl-terminal of the B chain (peptide No. 19), followed by peptide fragments of 6 to 15 amino acid residues of the B chain (peptide No. 8). Fraction C showed a higher absorbance to 7 to 16 amino acid residues of the B chain (peptide No. 5) compared with the absorbance of fraction B. Polyclonal insulin-binding IgGs may form a macromolecule complex with insulin through the multiple affinity sites of IgG molecules. Feline insulin-binding IgGs are multifocal and may be composed of multiple IgG components and insulin.

Presence of anti-insulin natural autoantibodies in healthy cats and its interference with immunoassay for serum insulin concentrations

A substance interfering with the enzyme-linked immunosorbent assay (ELISA) for feline insulin concentration was investigated in healthy cats. An insulin-binding substance isolated from feline serum showed 2 bands at 25 and 50 kDa in SDS-PAGE, suggesting the presence of immunoglobulin G (IgG). Insulin-binding IgG from healthy cats indeed reduced insulin immunoreactivity in the ELISA for determining insulin concentration. The insulin-binding IgG was polyclonal/polyreactive and showed certain specificity, high affinity, and high binding capacity, which was evaluated by liquid-phase radioimmunoassay with Scatchard plot analysis. Epitope analysis revealed that the insulin-binding IgG showed significant binding at residues A1-5 and B20-30 of the insulin molecule. Removal of the antibodies from serum enabled the determination of serum insulin concentrations by ELISA. Our data indicated that serum from healthy cats contained substantial amounts of natural autoantibodies combined with insulin, and that the antibodies interfered with the heterologous immunoassay for serum insulin concentration.

Severe Autoimmune Hypoglycemia With Insulin Antibodies Necessitating Plasmapheresis

OBJECTIVE

To report a case of autoimmune hypoglycemia.

METHODS

We describe the clinical course of a patient with autoimmune hypoglycemia, including results of biochemical and histocompatibility antigen studies, as well as the therapeutic intervention and follow-up.

RESULTS

A 77-year-old man presented with clinical manifestations of severe spontaneous hypoglycemia associated with extremely high levels of insulin (>300 mU/mL) and insulin antibodies (>100 U/mL) without any exogenous insulin administration. He had no other associated autoimmune disorder or exposure to the sulfhydryl group of drugs. Corticosteroid therapy was initiated, but the patient continued to have hypoglycemia and required plasmapheresis. The hypoglycemia resolved after plasmapheresis. During follow-up, the patient was treated with prednisone, the dose of which was tapered gradually. The insulin antibodies, which had decreased rapidly after plasmapheresis, gradually disappeared within a few months. The patient remained free of hypoglycemia as well as insulin antibodies 11 months after corticosteroid therapy was discontinued.

CONCLUSION

Although autoimmune hypoglycemia is an uncommon disorder, it should be considered in any patient with hypoglycemia in the setting of nonsuppressed insulin levels associated with insulin antibodies.

Autoimmune hypoglycemia

Autoimmune hypoglycemia is a rare but fascinating syndrome of hypoglycemia caused by the interaction of endogenous antibodies with insulin or the insulin receptor. Awareness of autoimmune hypoglycemia is important because the syndrome may produce severe neuroglycopenic symptoms and may be confused with the presence of an insulinoma. A correct diagnosis is important to avoid unnecessary surgical intervention in patients who are best treated with conservative support, watchful waiting, or in some cases, immunosuppressive therapy.

Diagnostic approach to adults with hypoglycemic disorders

Optimal conditions for confirming the presence and accurately diagnosing the type of hypoglycemic disorder occur at the time of a spontaneous spell. Otherwise, dynamic testing to generate conducive conditions should be conducted in any patient with a history of neuroglycopenic symptoms, regardless of relation to meal ingestion. Specific criteria regarding beta-cell polypeptide concentrations are required to establish hyperinsulinemia. Sulfonylureas in plasma should be measured with sensitive assays. In complex cases, the selective arterial calcium test may be a useful dynamic test.

Classification of hypoglycemic disorders

The classification of symptoms of hypoglycemia, namely, reactive versus fasting, based on segregation by timing in relation to meals is no longer useful from a clinical point of view. Every patient with neuroglycopenic symptoms, regardless of relation to food ingestion, requires comprehensive evaluation. Identification of the possible cause of hypoglycemia and selection of diagnostic modalities are facilitated by considering whether the patient appears to be healthy (with or without compensated coexistent disease) or ill (with a disease known to have a proclivity to develop hypoglycemia, or is hospitalized). Medications may mediate hypoglycemia in anybody, whether they appear healthy or ill.

Hypoglycemia

The diagnosis of a hypoglycemic disorder requires a high level of suspicion, careful assessment of the patient for the presence of mediating drugs or predisposing illness, and, when indicated, methodic evaluation of the basis of well-defined diagnostic criteria. The diagnostic burden is heaviest for healthy-appearing persons with episodes of confirmed neuroglycopenia. The author's criteria for insulin mediation of hypoglycemia are plasma insulin of 6 microU/mL or higher (radioimmunoassay), C-peptide of 200 pmol/L or higher (ICMA), proinsulin of 5 pmol/L or higher (ICMA), beta OH butyrate of 2.7 mmol/L or lower, and generous (> or = 25 mg/dL) response of plasma glucose to intravenous glucagon administered when the patient is hypoglycemic. Sulfonylurea should be sought in the plasma of any hypoglycemic patient, especially by an assay which can detect the second generation of these drugs.

Gastrointestinal endocrine tumours. Insulinoma

Fundamental to establishing a diagnosis of insulinoma is first to consider the diagnosis when presented with the constellation of symptoms and signs that indicate hypoglycaemia. Prominent and most convincing are manifestations of neuroglycopenia. Although hypoglycaemia can be caused by a number of disorders, the combination of hypoglycaemia and endogenous hyperinsulinaemia is diagnostic of insulinoma. Our criteria now include a glucose level of 40 mg/dl with a concomitant insulin level of 6 microU/ml, a C-peptide level exceeding 200 pmol/l, and negative screen for sulphonlyurea. Ancillary diagnostic tests or the use of insulin surrogates may offer helpful confirmation. Localization is still evolving, but in our hands pre-operative ultrasound is the best and only pre-operative test that we obtain in the usual situation. Expertise and experience with other modalities at other institutions offer reasonable but more costly alternatives. Intraoperative ultrasonography provides significant benefit in both tumour localization and delineating important related anatomy. Insulinomas are virtually all located in the pancreas; 90% are benign, single, and are generally firmer than surrounding normal pancreas. Extensive exposure may be required to identify and remove safely the tumour. Enucleation is our preferred technique, but distal pancreatectomy for tumours in the body or tail is an excellent method as well. Pancreatoduodenectomy is rarely necessary. Complications most commonly relate to leak of pancreatic secretions, causing pseudocyst, abscess, or fistula. except in MEN 1 syndrome, excision of a benign insulinoma equates with disease cure, and patients are often extraordinarily grateful as the change in their lives may be profound.