At a Glance
Vipoma (Verner-Morrison syndrome, pancreatic cholera, WDHA syndrome - for watery diarrhea, hypokalemia, and achlorhydria) is one of several rare types of functioning pancreatic neuroendocrine tumors (NETs) and accounts for 2-4% of all pancreatic NETs. Most cases are sporadic, but about 10% are associated with multiple endocrine neoplasia type 1 (MEN1). Vipomas are usually solitary tumors, larger than 3 cm in diameter, and occur in an intrapancreatic location in more than 95% of adult cases (tail of pancreas in 75% of cases). In children, vipomas occur in sympathetic ganglia and in the adrenal glands. Metastatic disease at the time of diagnosis is present in 70-80% of cases, but, as in other NETs, the degree of malignancy cannot be predicted by histological appearance.
Ectopic secretion of vasoactive intestinal polypeptide (VIP) by the tumor causes profound, high volume diarrhea (stool volume exceeds 700 mL/day in all patients), resulting in dehydration, hypokalemia, and achlorhydria (75% of cases). Symptoms associated with dehydration and hypokalemia include lethargy, nausea, vomiting, muscle weakness, and muscle cramps. Abdominal pain is mild or absent. Flushing episodes can occur (20% of cases) and are attributable to the vasodilator action of VIP. Other common findings include hyperglycemia and hypercalcemia.
Which Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
As for other gastroenteropancreatic neuroendocrine tumors (GEP-NETs), there are two steps involved in establishing the diagnosis:
confirming hypersecretion of the relevant hormone (VIP)
localizing the tumor (by imaging studies)(
Test Results Indicative of the Disorder
|Fasting VIP, serum|
|Usually >75 pg/mL|
Order fasting serum VIP for patients suspected of having vipoma (presenting with otherwise unexplained high volume secretory diarrhea, supported by low osmotic gap in a stool specimen). In vipoma, fasting serum VIP concentrations are usually greater than 75 pg/mL. A single elevated VIP concentration should be repeated. VIP concentrations are measured by radioimmunoassay.
Serum chromogranin A (CGA) is a nonspecific marker for well-differentiated neuroendocrine tumors that does not distinguish among the various tumor subtypes. CGA is usually elevated in GEP-NETs, including vipomas. Because CGA concentration correlates with tumor volume, it may be useful for staging, prognosis, and monitoring. CGA can be elevated in other conditions, including renal insufficiency or severe malabsorption syndrome.
What Lab Results Are Absolutely Confirmatory?
Histopathological evaluation (with the use of ancillary studies, including immunohistochemical stains for neuroendocrine markers if necessary) of the removed tumor or biopsy material (if performed) confirms the diagnosis.
Additional Issues of Clinical Importance
Delayed diagnosis can lead to adverse effects, including risks related to hypokalemia, as well as delay in treatment of the underlying condition, which is primarily surgical.
Errors in Interpretation
A single elevated fasting VIP concentration in the presence of secretory diarrhea should be repeated to establish the diagnosis of vipoma.
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