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Letters |
1
Institute of Clinical Chemistry,,
2
Department of Internal Medicine II,, and,
3
Department of Surgery, Ludwig-Maximilians-Universität Munich, Klinikum Grosshadern, D-81366 Munich, Germany
a Author for correspondence. Fax 49-89-7095-3240; e-mail
mvogeser{at}klch.med.uni-muenchen.de.
To the Editor:
A 72-year-old Caucasian man was admitted to our hospital in November 1999 for reanastomosis of an ileostoma that had been created after perforation of a sigmoid diverticulum with peritonitis. The past medical history of the patient was unremarkable except for angioneurotic edema of unknown etiology 14 years previously. The immediate postoperative course was uneventful, and the patient received glucose (400 g/L, 40 mL/h) via a central line. Because it was planned to reestablish enteral nutrition on day 7, glucose infusions were discontinued during the preceding night. At 0500 on day 7, the patient had a generalized seizure. Bedside testing revealed a nondetectable blood glucose concentration. After the patient received 100 mL of a glucose solution (500 g/L), the seizures stopped. During the following 24 h, his glucose concentration repeatedly fell to <2.8 mmol/L, requiring glucose administration; 36 h after the initial hypoglycemia, the patient was on full enteral nutrition, and glucose concentrations remained stable.
A serum sample obtained 1 h after the seizure revealed an extremely high insulin concentration (1746 mIU/L; reference interval, 6–35 mIU/L; IMx Insulin; Abbott) and a serum glucose concentration of 4.3 mmol/L, whereas C-peptide was increased approximately twofold above the upper reference limit (8.8 µg/L; reference interval, 0.8–4.0 µg/L; Immulite C-Peptide; DPC). In subsequent samples, insulin concentrations were lower, but they were still 5- to 15-fold above the upper reference limit. A computed tomography, obtained preoperatively, did not reveal a pancreatic mass.
To exclude an analytical artifact of insulin determination, samples were reanalyzed in serial dilutions up to 1:32 and with a different assay (Count-a-coat Insulin; DPC); this confirmed extreme hyperinsulinemia. Serum insulin antibodies (RIA) were 88 kilounits/L (reference interval, 0–5). On the basis of these findings, autoimmune hypoglycemia (AIH) (1) was suspected.
To confirm the diagnosis, the patient was evaluated by an
oral glucose challenge (75 g) after full recovery from surgery. Glucose
intolerance was observed with a serum glucose of 13.0 mmol/L after 60
min; insulin was increased to a peak concentration of 3162 mIU/L after
180 min, and symptomatic hypoglycemia occurred after 240 min (glucose,
1.8 mmol/L), at which point the study was terminated (Fig. 1
). Consequently, the patient was advised to eat at least six
small meals per day and to avoid meals rich in quickly absorbed
carbohydrates. In addition, he and his family were informed about the
management of hypoglycemia.
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Insulin autoantibodies are common in patients receiving exogenous insulin, but they can also be observed in individuals never treated with insulin, particularly in patients with autoimmune diseases [up to 30% (2)]. However, very few patients develop symptomatic hypoglycemia. It is assumed that in these cases, glucose administration causes excessive insulin response because the antibodies buffer most of the insulin secreted. When glucose concentrations return to normal, large amounts of antibody-bound insulin remain in the plasma and subsequently dissociate from the antibodies, leading to hypoglycemia (1). When glucose is administered in this situation (as in the initial event in our patient), hyperinsulinemia may be amplified, leading to further hypoglycemia several hours later.
AIH was first described in 1972 by Hirata and Ishizu (3).
Serum insulin concentrations typically are extremely high in AIH and
distinctly higher than in insulinoma. Almost 90% of reported AIH cases
are from Japan (4); this is explained by the increased
susceptibility to AIH of individuals with the HLA-DR4 allele
DRB10406, which has a high prevalence in Japan
(5). In other patients, AIH frequently is associated with
gammopathies (4)(6). The serum electrophoresis
and immune fixation technique in the case presented here disclosed
discrete monoclonal IgG-
. Tests for antinuclear and antithyroid
antibodies were negative; thyroid-stimulating hormone was 3.1
mIU/L. The differential diagnosis of hypoglycemia with high
insulin concentrations includes exogenous insulin, sulfonyl-ureas,
insulinoma, and AIH. However, in all conditions but AIH insulin
concentrations are 10-fold lower.
The hypoglycemia in AIH can usually be controlled by dietary measures. However, some patients require immunosuppressive therapy or even pancreatic resection (1)(4).
Our case demonstrates that AIH is a rare but important cause of life-threatening hypoglycemia. To the best of our knowledge, this is the first reported case of AIH presenting as a life-threatening complication in the postoperative period after discontinuation of parenteral nutrition.
References
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