Medical therapy of VIPomas

VIP-secreting tumors are rare, but they produce a dramatic clinical picture, the most prominent feature of which is profuse, watery diarrhea and hypokalemia. A definitive diagnosis is aided by the determination of plasma VIP concentrations through the use of the sensitive radioimmunoassays that are now available. Intestinal secretion resulting from the direct action of VIP on the intestinal epithelial cell receptors accounts for the loss of fluid and electrolytes in patients with VIPoma. The hypokalemia is the result of passive and VIP-induced active secretion of potassium by colonic epithelial cells. Surgery is the most definitive treatment of VIPoma; pharmacotherapy is extremely important in controlling symptoms and stabilizing the patient prior to surgery. Sandostatin and glucocorticoids are well established agents in the management of the secretory diarrhea; other pharmacologic agents, including clonidine, indomethacin, phenothiazines, lithium carbonate, and propranolol, may be helpful in selected patients but require further study. The most potent and promising drug for the treatment of VIPoma is a new peptidomimetic agent--Sandostatin. This metabolically stable synthetic analogue of somatostatin appears, in part, to inhibit the release of VIP from the tumor and the secretion of chloride by the intestine. In addition to controlling the diarrhea, it may have a direct effect on the tumor in reducing its size.