Hypoglycaemia caused by atypical insulin antibodies in a patient with benign monoclonal gammopathy.
We describe a 48-year-old woman with recurrent severe hypoglycaemia apparently caused by a paraprotein with insulin-binding capacity. Very high fasting values were found for serum insulin (170 and > 250 mU l-1) as well as for proinsulin 125 pmol l-1 and an insulinoma was suspected. Hypoglycaemia developed after an oral glucose tolerance (OGTT) test but not during fasting for 48 h. Free insulin and C-peptide were normal during OGTT whereas serum insulin was very high. 125I-insulin binding to serum, determined with a polyethylene glycol (PEG) precipitation method was high (40%), and equally high after addition of 1.7 x 10(-5) mol l-1 cold insulin to estimate non-specific binding. By adding very high concentrations of cold insulin, displacement of 125I-insulin bound to serum was found (50% displacement at 4 x 10(-5) mol l-1). No immunoglobulin G (IgG) insulin antibodies were detected by radioimmunoelectrophoresis. On agarose electrophoresis a small paraprotein (4 g l-1) in the gamma-globulin fraction was detected. 125I-insulin binding to this paraprotein was demonstrated. We conclude that if insulin autoantibodies are suspected as a cause of hypoglycaemia screening for insulin antibodies should always be done with a PEG-precipitation method.
Arnqvist
H J
HJ
Department of Internal Medicine, Faculty of Health Sciences, Linköping University, Sweden.
Halban
P A
PA
Mathiesen
U L
UL
Zahnd
G
G
von Schenck
H
H
D001323:Autoantibodies / Q000097:blood*; D005260:Female; D006801:Humans; D007003:Hypoglycemia / Q000276:immunology*; D007328:Insulin / Q000097:blood; D007330:Insulin Antibodies / Q000097:blood*; D008875:Middle Aged; D008998:Monoclonal Gammopathy of Undetermined Significance / Q000150:complications* / Q000276:immunology
D001323:Autoantibodies; D007328:Insulin; D007330:Insulin Antibodies