Vasoactive Intestinal Peptide Tumor as the Cause of Persistent Diarrhea: A Diagnostic Challenge

Although chronic diarrhea is frequent, some of its causes are rare, namely, neuroendocrine tumors (NETs). Due to their rarity and non-specific symptoms, such as diarrhea, they are often underdiagnosed. An 80-year-old woman presented to the emergency department due to emesis and watery diarrhea. Blood tests showed acute kidney injury, hypokalemia, and metabolic acidosis. An abdominal computed tomography revealed a 51 mm pancreatic lesion. An endoscopic ultrasound-guided biopsy raised the hypothesis of a NET. The patient refused surgery and was lost to follow-up. At the eighth hospitalization, 11 months later, the suspicion of a vasoactive intestinal peptide tumor (VIPoma) was raised and confirmed by assessing the vasoactive intestinal peptide (VIP) levels (>100 pmol/L). Octreotide was started with the resolution of the symptoms. 68Ga-DOTANOC positron emission tomography/computed tomography excluded metastatic disease. After six months of octreotide therapy, the tumor shrunk 13 mm in maximum diameter. At the last follow-up, one year later, she remained asymptomatic. The delayed diagnosis of VIPoma led to multiple life-threatening episodes. This case highlights the importance of considering all potential differential diagnoses of common symptoms such as diarrhea. Although VIPomas are rare, clinicians should be aware of this entity and suspect this diagnosis in patients with chronic diarrhea with a poor response to standard antidiarrheal agents. Somatostatin analogs should be promptly prescribed for symptom control and tumor progression prevention in patients who refuse surgery or have unresectable tumors. Tumor shrinkage might also be observed in these cases.