INSULINOMA
Most common of all functioning pancreatic endocrine tumors (PET)
Highest incidence in 4th to 6th decade
Women are slightly more affected
All insulinomas are located in the pancreas and tumors are equally distributed
90% are solitary and 90% are small ( < 2cm)
10% are multiple (always associated with MEN 1) and 10% are malignant
Clinical features: Abdominal discomfort, sweating, hunger, dizziness, diplopia, overeating, and obesity
Whipple’s triad
Symptoms of hypoglycemia after fasting or exercise
Symptoms of hypoglycemia (blood sugar < 45mg %)
Immediate relief after I.V. glucose administration
Diagnosis
A fasting test that lasts for upto 72 hours is the most sensitive test
Insulin, Proinsulin, C-peptide and blood glucose are measured at 1 to 2 hour intervals to demonstrate high secretion of insulin in relation to blood glucose
Continuous C-peptide levels demonstrate the endogenous insulin secretion and exclude factitious hypoglycemia caused by insulin injection
Insulin radioimmunoassay
Insulin level > 7 µU/ml
Insulin/glucose ration > 0.3
Increased circulating C-peptide
Proinsulin level >24% of total insulin signifies insulinoma
Proinsulin level >40% of total insulin signifies malignant insulinoma
For preoperative localization: Endoscopic ultrasound(EUS) has the highest sensitivity
Treatment
Enucleationis the treatment of choice for benign insulinomas
For superficial tumors: laparoscopic enucleation
Tumors located deep in the body or tail and those in close proximity to pancreatic duct: distal pancreatectomy
Diazoxide suppresses insulin secretion and offers good control of hypoglycemia
Malignant insulinomas: aggressive resection
When surgery cannot be applied for malignant insulinomas: Chemotherapy (Doxorubicin + Streptozocin)