Tentative Diagnosis: The tentative diagnosis is a functional pancreatic islet cell tumor (insulinoma). The classic presentation—a middle-aged dog of a predisposed breed with episodic neurologic signs related to fasting or exercise, rapid response to sugar administration, and a documented profound hypoglycemia during an event—is highly pathognomonic for this disease. This presentation fulfills Whipple's Triad.
DDx: Other causes of profound hypoglycemia in an adult dog include sepsis, severe liver failure, hypoadrenocorticism (Addison's disease), xylitol toxicity, or a large non-pancreatic tumor (paraneoplastic hypoglycemia). However, the episodic nature and the otherwise completely normal physical exam and history make these differentials much less likely.
Further Diagnostic Test(s): The diagnostic plan is to first confirm the cause of the hypoglycemia and then to stage the disease to guide treatment.
Confirmation Test: The definitive diagnostic test is the paired insulin and glucose concentration performed on the blood sample taken during the hypoglycemic episode.
Results:
Glucose: 38 mg/dL (Markedly Low) [Ref: 75 - 125 mg/dL]
Insulin: 45 µU/mL (Inappropriately High) [Ref: 5 - 20 µU/mL]
Interpretation: This result is diagnostic for an insulinoma. In a healthy animal, when blood glucose is critically low, insulin secretion should be shut down (levels <5 µU/mL). The presence of a normal to high insulin level in the face of profound hypoglycemia confirms the autonomous, unregulated secretion of insulin from a tumor.
Staging: To assess the extent of the disease, imaging was performed.
Three-View Thoracic Radiographs: No evidence of metastatic disease was found.
Abdominal Ultrasound: A 1.8 cm, hypoechoic nodule was identified on the right lobe of the pancreas. The medial iliac lymph nodes were noted to be enlarged and rounded, which is suspicious for metastasis.
Definitive Diagnosis:
Functional Pancreatic Islet Cell Tumor (Insulinoma) with suspected regional lymph node metastasis. More information can be found at the
Treatment Plan: The treatment plan involves immediate stabilization, followed by definitive surgical intervention and a long-term medical management strategy.
Immediate Stabilization: Following the diagnostic blood draw, Louie was given a slow intravenous bolus of 50% dextrose, to which he responded immediately. He was then maintained on a constant rate infusion of fluids containing 2.5% dextrose to prevent further hypoglycemia.
Definitive Treatment: The treatment of choice is surgical.
Surgical Plan: The recommendation is for an exploratory laparotomy with the goal of performing a partial pancreatectomy to remove the primary tumor nodule and debulking/removing the enlarged regional lymph nodes for biopsy. The owners were counseled that surgery can be curative but that recurrence is common due to micrometastasis.
Long-Term Medical Management:
Dietary: Louie will be transitioned to a diet high in protein, fat, and complex carbohydrates, fed as 3-4 small meals throughout the day to prevent dramatic swings in blood glucose.
Pharmacologic: Post-operatively, or if surgery is declined, medical management will be initiated. The first-line therapy is prednisone, a corticosteroid that counteracts the effects of insulin. If clinical signs persist, a second medication like diazoxide, which directly inhibits insulin secretion from the tumor, may be added.
Owner Education: The owner was instructed on how to recognize early signs of a hypoglycemic episode and how to manage it at home by rubbing Karo syrup or honey on Louie's gums, followed immediately by feeding a small meal. They were advised to avoid intense exercise and prolonged fasting.
