Віпома

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, metabolic acidosis, 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 (1).

Lethargy, muscular weakness, nausea, vomiting, and crampy abdominal pain occur frequently.

Flushing similar to that of carcinoid syndrome occurs in 20% of patients during attacks of diarrhea.

• Confirmation of secretory diarrhea

• Serum vasoactive intestinal peptide (VIP) levels

• Endoscopic ultrasound, positron emission tomography (PET), or scintigraphy can localize

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). 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 bowel disease.

Patients with elevated VIP levels should have tumor localization studies, such as endoscopic ultrasound, 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 occurs in 50% of patients. The etiology for hypercalcemia is not entirely clear, but contributing factors may include severe dehydration, concurrent multiple endocrine neoplasia (MEN), and calcitropic peptide secreted by the tumor (1).

• Fluid and electrolyte replacement

• Octreotide or lanreotide

• Surgical resection for localized disease

Initially, fluids and electrolytes must be replaced. Bicarbonate must be given to replace that due to fecal loss and avoid acidosis. Because fecal losses of water and electrolytes increase as rehydration is achieved, continual IV replacement may become difficult.

The somatostatin analog octreotide usually controls diarrhea, but large doses may be needed. Patients who respond initially to octreotide may benefit from a long-acting octreotide formulation or lanreotide. Patients using octreotide or lanreotide may also need to take supplemental pancreatic enzymes because these somatostatin analogs suppress 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 (1).

The combination of streptozocin and doxorubicin may reduce diarrhea and tumor mass if objective response occurs (in 50 to 60%). Chemotherapies under investigation for vipoma include temozolomide-based regimens, everolimus, and sunitinib (1). Chemotherapy is not curative.