What are the characteristic symptoms of somatostatinoma?

Characteristics of Somatostatinoma

The characteristic symptoms of somatostatinoma are mild diabetes, diarrhea/steatorrhea, and gallstones (cholelithiasis), known as the "somatostatinoma triad" or "inhibitory syndrome." 1

Clinical Presentation

Somatostatinoma is a rare endocrine tumor that presents with a classic triad of symptoms:

• Mild diabetes mellitus - Results from somatostatin's inhibitory effect on insulin secretion 2, 1
• Diarrhea/steatorrhea - Occurs due to somatostatin's inhibitory effect on digestive enzyme secretion 1, 3
• Cholelithiasis (gallstones) - Develops because somatostatin suppresses gallbladder motility 1, 4

Epidemiology and Pathophysiology

• Somatostatinomas comprise approximately 1% of all gastroenteropancreatic endocrine neoplasms 1
• These tumors may be located in:
  • Pancreas (where inhibitory syndrome is more common - 18.5% of cases) 4
  • Duodenum (most frequent site, but inhibitory syndrome is rare - 2.5% of cases) 1, 4
  • Other locations such as jejunum (extremely rare) 1

Mechanism of Symptoms

The symptoms result from excessive somatostatin release, which has inhibitory effects on multiple systems:

• Somatostatin inhibits insulin secretion, leading to glucose intolerance and mild diabetes 2, 3
• Pancreatic exocrine function is suppressed, causing malabsorption and steatorrhea 3, 4
• Gallbladder contractility is reduced, promoting gallstone formation 1, 4

Clinical Considerations

• Many somatostatinomas are non-functional and may present with obstructive symptoms rather than the classic triad 1
• By the time of diagnosis, nearly two-thirds have already metastasized to regional lymph nodes or liver 1
• Somatostatinomas may be associated with genetic syndromes:
  • Neurofibromatosis type 1 (particularly duodenal somatostatinomas - 43.2% of cases) 1, 4
  • Multiple Endocrine Neoplasia type 1 1
  • Von Hippel-Lindau syndrome 1

Diagnostic Approach

• Elevated plasma somatostatin-like immunoreactivity is diagnostic 3, 5
• The National Comprehensive Cancer Network recommends multiphasic CT/MRI for tumor localization 2
• Somatostatin receptor scintigraphy (SRS) can be effective in detecting primary and metastatic lesions 6

Treatment Options

• Surgical resection is the primary treatment when possible 1, 4
• Octreotide (somatostatin analog) therapy can effectively decrease plasma somatostatin levels and improve symptoms in patients with the somatostatinoma syndrome 6
• Streptozotocin has shown efficacy in reducing tumor volume and hypersomatostatinemia in disseminated disease 5

Prognosis

• The overall 5-year survival rate is approximately 75.2% 4
• Patients without metastases have excellent outcomes (100% 5-year survival) 4
• Those with metastases have a significantly worse prognosis (59.9% 5-year survival) 4