What are the characteristic symptoms of somatostatinoma?

Characteristics of Somatostatinoma

The characteristic symptoms of somatostatinoma are mild diabetes, diarrhea, and gallstones. 1

Clinical Presentation

Somatostatinomas are rare neuroendocrine tumors that secrete excessive amounts of somatostatin, leading to a constellation of symptoms known as the "somatostatinoma syndrome." This syndrome includes:

• Mild diabetes mellitus (due to inhibition of insulin secretion) 2, 1
• Chronic diarrhea (due to inhibition of pancreatic and intestinal secretions) 1, 3
• Gallstones/gallbladder dysfunction (due to inhibition of gallbladder contractility and bile flow) 1, 4

Pathophysiology

The clinical manifestations of somatostatinoma result from the inhibitory effects of somatostatin on multiple physiological processes:

• Somatostatin inhibits insulin secretion, leading to mild diabetes 2
• Somatostatin inhibits pancreatic exocrine function and intestinal absorption, causing diarrhea 1
• Somatostatin decreases gallbladder contractility and bile secretion, promoting gallstone formation 4

Anatomical Distribution and Clinical Differences

Somatostatinomas can originate in different locations, with distinct clinical presentations:

• Pancreatic somatostatinomas (46.8% of cases):

  • More likely to present with the classic triad of symptoms (18.5% vs 2.5% in duodenal tumors) 1
  • Typically larger in size (>20mm in 85.5% of cases) 1
  • Often multisecretory (33.3% of cases) 1

• Duodenal somatostatinomas (53.2% of cases):

  • Less likely to present with the classic syndrome 1, 3
  • More frequently associated with neurofibromatosis (43.2% of cases) 1
  • Often contain psammoma bodies (49.4% of cases) 1

Diagnostic Approach

Diagnosis of somatostatinoma is challenging due to the rarity and nonspecific symptoms:

• Laboratory findings include elevated plasma somatostatin levels 5
• Imaging studies such as multiphasic CT/MRI help localize the tumor 2
• Somatostatin receptor scintigraphy (SRS) can detect primary and metastatic lesions 5
• Definitive diagnosis requires histological and immunohistochemical confirmation 3

Management

Treatment approaches for somatostatinomas include:

• Surgical resection is the primary treatment for localized disease 4, 6
• Whipple procedure (pancreaticoduodenectomy) is common for pancreatic head tumors 6
• Somatostatin analogues (octreotide, lanreotide) can help control symptoms and may stabilize tumor growth 5
• Even with metastatic disease, 5-year survival is approximately 40% 6

Clinical Pitfalls and Caveats

• Somatostatinomas are often diagnosed late due to nonspecific symptoms 4
• Metastases are common at diagnosis, particularly to liver and lymph nodes 4, 6
• Tumors >3cm, poor differentiation, and incomplete resection predict worse outcomes 6
• Unlike insulinomas, somatostatinomas respond favorably to somatostatin analogues 5
• Somatostatinomas have a higher malignancy rate compared to other pancreatic neuroendocrine tumors 1