Makindo Medical Notes

Both VIPomas and villous adenomas classically can cause profuse diarrhoea and hypokalaemia.

About

• VIPomas are rare neuroendocrine tumours that secrete vasoactive intestinal polypeptide (VIP), leading to significant gastrointestinal symptoms.
• They are most commonly found in the pancreas but can occasionally arise in other locations, such as the adrenal glands.
• The classic presentation of a VIPoma is the triad of watery diarrhoea, hypokalemia, and achlorhydria (referred to as WDHA syndrome).
• The VIP gene responsible for producing the vasoactive intestinal polypeptide is located on chromosome 6.

Aetiology

• VIP stimulates the production of cyclic Adenosine Monophosphate (cAMP) in the gut, increasing fluid secretion and motility.
• These tumours are usually found in the pancreas but can rarely originate from other neuroendocrine tissues such as ganglioneuroblastomas in the sympathetic chain or adrenal cortex.
• The overproduction of VIP leads to water and potassium loss in the intestines, resulting in the characteristic symptoms of secretory diarrhoea and hypokalemia.

Clinical Features

• Patients present with watery (secretory) diarrhoea, often exceeding 3 liters per day, leading to dehydration.
• Other symptoms include facial flushing, significant weight loss, and abdominal colic.
• In advanced cases, hepatomegaly may be present due to liver metastases.
• Lethargy, muscle weakness, and cramps may result from hypokalemia.

Investigations

• U&E: Shows hypokalaemia and a non-anion gap metabolic acidosis due to the loss of potassium and bicarbonate in stool.
• Glucose: Mild hyperglycaemia may be seen, as these tumours can interfere with insulin secretion.
• Plasma VIP levels are typically elevated, along with raised levels of other neuroendocrine markers such as pancreatic polypeptide.
• CT/MRI of the abdomen: Imaging is often used to locate the tumour and assess for metastases.

Management

• Fluid and electrolyte replacement is critical to manage dehydration and hypokalemia.
• Octreotide, a somatostatin analogue, can help reduce diarrhoea by inhibiting the release of VIP and other hormones.
• Surgical resection is the treatment of choice for localized, non-metastatic tumours. For metastatic disease, management is typically palliative, focusing on symptom control.