Beta-cell Adenomas without Hyperinsulinemia with use of Highly Specific Insulin Radioimmunoassays: case Report and Review of Literature

Objective:�Toreportacaseofaproinsulin-secreting� isletcelladenomainwhichthediagnosiswasobscuredby� anultraspecificinsulinassay. � Methods:�Wedescribethecaseofa�46-year-oldwom- an,�whopresentedwithfastinghypoglycemiaandappro- priatelylowinsulinvalues. � Results:�Aprolongedsupervisedfastproducedsymp- tomatichypoglycemia� (20� mg/dL)� afteronly� 7� hours.� Duringtheentirefastingtest,�highlyspecificinsulinre- mainedat� 200�pmol/Linall� determinationswhenhypoglycemiawaspresent;�expected� value,�<5�pmol/L).�Magneticresonanceimagingandendo- scopicultrasonographyconfirmedthepresenceofa�2.5-cm� tumorintheheadofthepancreas.�Aproinsulin-secreting� isletcelltumorwasdiagnosed.�Surgicalresectionofthetu- morwassuccessfullyaccomplished,�butdiabetesmellitus� developed�4�monthspostoperatively. � Conclusion:�Thediagnosisofahypoglycemia-pro- ducingpancreaticadenomacanbemissedwhenanultra- specificinsulinassayisused.�Thedirectmeasurementof� proinsulinestablishedthediagnosisinthiscase.�(Endocr Pract. 2010;16:660-663)