Characteristics of Somatostatinoma
The characteristic symptoms of somatostatinoma are mild diabetes, diarrhea, and gallstones (cholelithiasis). 1, 2
Clinical Presentation
Somatostatinomas are rare endocrine tumors with a specific constellation of symptoms often referred to as the "somatostatinoma syndrome," which includes:
- Mild diabetes mellitus - occurs due to somatostatin's inhibitory effect on insulin secretion 1
- Diarrhea/steatorrhea - results from maldigestion due to somatostatin's inhibitory effects on digestive processes 2, 3
- Gallstones (cholelithiasis) - develops due to inhibition of gallbladder contractility and bile flow 2, 3
This triad of symptoms is present in approximately 18.5% of pancreatic somatostatinomas but only about 2.5% of duodenal somatostatinomas 3.
Pathophysiology
The symptoms of somatostatinoma directly relate to the physiological effects of excess somatostatin:
- Somatostatin inhibits insulin secretion, leading to glucose intolerance and mild diabetes 1
- Inhibition of digestive enzyme secretion and gastrointestinal motility causes malabsorption and diarrhea 2
- Decreased gallbladder contractility and reduced bile flow contribute to gallstone formation 3
Important Clinical Considerations
When evaluating patients with suspected somatostatinoma:
- Most patients present with nonspecific abdominal symptoms rather than the classic triad 4
- The majority of these tumors are located in the pancreas (particularly the head) or duodenum 3
- Pancreatic somatostatinomas are more likely to present with the classic syndrome compared to duodenal ones 3
- Duodenal somatostatinomas have a high association with von Recklinghausen's disease (neurofibromatosis type 1), occurring in about 43.2% of cases 3
Diagnostic Approach
For suspected cases:
- Multiphasic CT/MRI is recommended to localize the tumor 1
- Somatostatin receptor scintigraphy (SRS) using octreotide can effectively visualize these tumors 5
- Measurement of plasma somatostatin levels can confirm the diagnosis 5
Treatment Considerations
Management typically involves:
- Surgical resection (often Whipple procedure for pancreatic head tumors) 2, 4
- Octreotide therapy can effectively decrease plasma somatostatin levels and improve symptoms 5
- Even with metastatic disease, 5-year survival is approximately 40% 4
Common Pitfalls
- Misdiagnosis is common due to the rarity of these tumors and nonspecific symptoms 2
- The absence of the classic triad does not rule out somatostatinoma, as many patients present with only nonspecific abdominal symptoms 4, 3
- These tumors are often large (average 5cm) at diagnosis and frequently have metastasized to regional lymph nodes or liver 4