Vipomas are a type of pancreatic endocrine tumor that arises from islet cells. Of these tumors, 50 to 75% are malignant, and some may be quite large (7 cm) at diagnosis. In about 6%, vipoma occurs as part of multiple endocrine neoplasia Overview of Multiple Endocrine Neoplasias (MEN) The multiple endocrine neoplasia (MEN) syndromes comprise 3 genetically distinct familial diseases involving adenomatous hyperplasia and malignant tumors in several endocrine glands. MEN 1 involves... read more .
(See also Overview of Pancreatic Endocrine Tumors Overview of Pancreatic Endocrine Tumors Pancreatic endocrine tumors arise from islet and gastrin-producing cells and often produce many hormones. Although these tumors develop most often in the pancreas, they may appear in other organs... read more .)
The major symptoms of vipoma are prolonged massive watery diarrhea (fasting stool volume > 750 to 1000 mL/day and nonfasting volumes of > 3000 mL/day) and symptoms of hypokalemia Symptoms and Signs Hypokalemia is serum potassium concentration 3.5 mEq/L ( 3.5 mmol/L) caused by a deficit in total body potassium stores or abnormal movement of potassium into cells. The most common cause is... read more , metabolic acidosis Symptoms and Signs Metabolic acidosis is primary reduction in bicarbonate (HCO3−), typically with compensatory reduction in carbon dioxide partial pressure (Pco2); pH may be markedly low or slightly subnormal... read more , and dehydration. In half of patients, diarrhea is constant; in the rest, diarrhea severity varies over time. About 33% of patients have diarrhea < 1 year before diagnosis, but 25% have diarrhea ≥ 5 years before diagnosis.
Lethargy, muscular weakness, nausea, vomiting, and crampy abdominal pain occur frequently.
Flushing similar to that of carcinoid syndrome Symptoms and Signs Carcinoid syndrome develops in some people with carcinoid tumors and is characterized by cutaneous flushing, abdominal cramps, and diarrhea. Right-sided valvular heart disease may develop after... read more occurs in 20% of patients during attacks of diarrhea.
Diagnosis of vipoma requires demonstration of secretory diarrhea (stool osmolality is close to plasma osmolality, and twice the sum of sodium and potassium concentration in the stool accounts for all measured stool osmolality). Other causes of secretory diarrhea and, in particular, laxative abuse must be excluded (see testing of diarrhea Testing Stool is 60 to 90% water. In Western society, stool amount is 100 to 200 g/day in healthy adults and 10 g/kg/day in infants, depending on the amount of unabsorbable dietary material (mainly... read more ). In such patients, serum VIP levels should be measured (ideally during a bout of diarrhea). Markedly elevated levels establish the diagnosis, but mild elevations may occur with short bowel syndrome and inflammatory diseases. Patients with elevated VIP levels should have tumor localization studies, such as endoscopic ultrasonography, PET, and octreotide scintigraphy or arteriography to localize metastases.
Electrolytes and complete blood count should be measured. Hyperglycemia and impaired glucose tolerance occur in ≤ 50% of patients. Hypercalcemia Hypercalcemia Hypercalcemia is a total serum calcium concentration > 10.4 mg/dL (> 2.60 mmol/L) or ionized serum calcium > 5.2 mg/dL (> 1.30 mmol/L). Principal causes include hyperparathyroidism, vitamin... read more occurs in 50% of patients.
Initially, fluids and electrolytes must be replaced. Bicarbonate must be given to replace fecal loss and avoid acidosis. Because fecal losses of water and electrolytes increase as rehydration is achieved, continual IV replacement may become difficult.
Octreotide usually controls diarrhea, but large doses may be needed. Responders may benefit from a long-acting octreotide formulation given 20 to 30 mg IM once a month. Patients using octreotide may also need to take supplemental pancreatic enzymes because octreotide suppresses pancreatic enzyme secretion.
Tumor resection is curative in 50% of patients with a localized tumor. In patients with metastatic tumor, resection of all visible tumor may provide temporary relief of symptoms. The combination of streptozocin and doxorubicin may reduce diarrhea and tumor mass if objective response occurs (in 50 to 60%). Newer chemotherapies under investigation for vipoma include temozolomide-based regimens, everolimus, or sunitinib. Chemotherapy is not curative.
More than half of vipomas are malignant.
Copious watery diarrhea (often 1 to 3 L/day) is common, often resulting in electrolyte abnormalities and/or dehydration.
Patients with confirmed watery diarrhea should have their serum vasoactive intestinal peptide (VIP) levels measured (ideally during a bout of diarrhea).
Localize tumors with endoscopic ultrasonography, positron emission tomography (PET), or octreotide scintigraphy or arteriography.
Remove tumors surgically when possible and suppress diarrhea with octreotide.