Mechanism(s):
(1) release of one or more compounds active on the small and/or large bowel. Vasoactive intestinal peptide (VIP) is a common cause but other compounds may be involved alone or in combination (prostaglandins, gastrin, substance P, serotonin, etc).
(2) malabsorption
Tumors associated with diarrhea:
(1) villous adenoma with secretory diarrhea (WDHA syndrome)
(2) hepatocellular carcinoma
(3) lung cancer, especially small cell
(4) medullary carcinoma of the thyroid
(5) Hodgkin’s disease
(6) neuroendocrine tumor (carcinoid, ganglioneuroblastoma, pheochromocytoma, other)
Features:
(1) onset or worsening of diarrhea, which may appeaer before the underlying tumor is recognized
(2) severity paralleling tumor burden (better if tumor resected, worse if it progresses)
Workup:
(1) stool analysis to determine the type of diarrhea (secretory vs other causes)
(2) serum concentrations of VIP, gastrin and other hormones
(3) analysis of resected tumor (immunohistochemistry, gene analysis, chemical assay)
Identifying causative biochemicals can help guide therapy. For example, if prostaglandins are implicated in the diarrhea then therapy with indomethacin may be helpful (Saban et al, Steven et al).
Differential diagnosis:
(1) radiation enteritis
(2) chemotherapy-related diarrhea
(3) infectious diarrhea
(4) post-operative dumping syndrome
