Pancreatic neuroendocrine tumors: VIPoma
What is a VIPoma?
A pancreatic neuroendocrine tumor which secretes vasoactive intestinal peptide (VIP) is called VIPoma. These rare tumors occur with a frequency of 1 per 10,000,000 per year. These tumors arise in the pancreas 90% of the time, but have also been described in the colon, bronchus, adrenals, liver, and sympathetic ganglia. Adults typically present between ages 30 and 50 years. Children can present with these tumors between 2 and 4 years of age. VIPomas are typically solitary and greater than 3 centimeters in diameter with 75% located in the tail of the pancreas. Sixty to eighty percent are metastatic at the time of diagnosis.
VIP is a hormone that stimulates the secretion and inhibits the absorption of sodium, chloride, potassium and water within the small intestine and increases bowel motility. These actions lead to a secretory diarrhea, hypokalemia (low potassium), and dehydration. The VIPoma syndrome is also commonly called Verner-Morrison syndrome, pancreatic cholera syndrome, or the WDHA syndrome. The last term reflects the common symptoms associated with these neuroendocrine tumors: watery diarrhea, hypokalemia, and achlorhydria. The secretory diarrhea associated with these tumors can be profound. Stool volumes of greater than three liters per day occur in 70% of these patients. Volumes less than 700 ml/day without treatment essentially exclude the diagnosis. The diarrhea persists despite fasting and is odorless and tea-colored. Chemical evaluation of the stool demonstrates a high sodium load and a low stool osmolal gap. Hypokalemia has been reported in most patients with VIPoma and can be accompanied by lethargy, nausea, and muscular discomfort. In patients with secretory diarrhea and hypokalemia suspected of having VIPoma, a fasting plasma VIP level should be measured.