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Insulinoma

Issue Description
When a dog has insulinoma, a tumor is present in the pancreas. This health condition causes insulin production to increase, which can cause hypoglycemia in dogs. Although insulinoma can affect breeds of all ages, older dogs are most likely to be diagnosed. Insulinoma is a disease of middle-aged to older dogs, with the mean age of affected dogs being 8.9 years (range: 3 to 15 years).


Causes
Insulinomas most commonly affect middle-aged to older dogs with no sex predilection. Unlike in humans, the majority of insulinomas in dogs are malignant, with up to 50% or more of affected dogs having metastasis at the time of diagnosis. Metastasis to the regional lymph nodes, liver, and mesentery is most common.

Symptoms
Hunger, behavior changes, muscle fasciculations, weakness, ataxia, or seizures can be seen and are often exacerbated by exercise and/or fasting. Eating can also result in clinical signs because of excessive insulin release.

Diagnosis
  • The typical presentation for a dog with insulinoma is a large-breed dog with a history of weakness, ataxia, or seizures, signs that may be exacerbated with exercise or fasting.
  • Physical examination findings are often within normal limits.
  • The most consistent laboratory abnormality is a fasting hypoglycemia.
  • Presumptive diagnosis is made with an abnormal insulin-glucose pair, with normal to elevated insulin levels in the face of low glucose levels.
  • Abdominal ultrasonography may be useful to detect nodules in the pancreas as well as metastatic disease in the abdomen. Intraoperative ultrasonography may be useful if nodules cannot be detected by visual inspection.

  • Additional diagnostic tests may help support the diagnosis of insulinoma but typically are not as sensitive as the insulin-glucose pair and abdominal ultrasonography.


    Clinical Staging System
  • Stage I: Insulinoma confined to the pancreas
  • Stage II: Insulinoma in the pancreas and regional lymph nodes
  • Stage III: Insulinoma with distant metastase
  • Treatment
    Surgery is the initial treatment of choice for insulinoma. Blood glucose must be normalized before, during, and after surgery. This is important because palpation of the nodules during surgery can result in insulin release. Palpation allows localization of the nodules in the majority of cases. Insulinomas tend to occur in the right and left lobes of the pancreas with equal frequency. Nondiscriminatory removal of pancreatic tissue is not recommended. Removal of the nodules can be performed by nodulectomy or partial or total pancreatectomy. Exploration with biopsy of suspicious areas in the abdomen should be performed. Metastasis has been reported in 36% to 51% of dogs at the time of initial surgery. Metastasis is most common to the liver and lymph nodes but has also been reported in the intestines, mesentery, spleen, and kidneys. Metastatic disease should be debulked as much as possible, as this may provide significant improvement in clinical signs.

    Dogs with tumors confined to the pancreas(stage I) or to the pancreas and regional nodes (stage II) have a median survival of approximately 1.5 years, while dogs that have metastasis beyond the nodes(stage III) have a median survival of less than 6 months.


    Pronosis
    Remission and survival in dogs with insulinoma following surgery depend on the clinical stage at the time of diagnosis. The median survival time of all affected dogs is approximately 12 months.

    Favorable Criteria
  • Dogs with tumors confined to the pancreas (stage I) have a longer remission time (defined as the period of euglycemia) than dogs whose tumors have metastasized. Dogs with stage I disease have a median remission time of approximately 14 months versus approximately 1 month for stage II or III dogs.
  • Dogs with tumors confined to the pancreas (stage I) or to the pancreas and regional nodes (stage II) have a longer survival time than dogs with tumors that are metastatic beyond the nodes (stage III). Dogs with stage I or II disease have a median survival of approximately 1.5 years, while dogs with stage III disease have a median survival of 6 months or less.
  • Partial pancreatectomy yields longer survival times than nodulectomy.

  • Unfavorable Criteria
  • Total pancreatectomy is associated with high morbidity and mortality.
  • Tumors in the body of the pancreas are more difficult to remove than tumors in the limbs of the pancreas.
  • Persistent postoperative hypoglycemia indicates that a residual tumor (either primary or metastatic) exists.


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