Clinical Rounds: Insulinoma in a senior pit bull

The Clinical Rounds team is from the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, The University of Tennessee, Knoxville, Tennessee.

Clinical rounds coordinator: Jeanne Larson, DVM, DACVIM (oncology)

Internal medicine: Lauren Adelman, DVM

Radiology: Federica Morandi, DMV, MS, DECVDI, DACVR

Clinical pathology: Lisa Viesselmann, DVM

Surgery: Christian Latimer, DVM

Anatomic pathology: Lani Bower, DVM

Medical oncology: Emily Manor, DVM

Dr. Jeanne LarsonInsulinomas are uncommon in dogs and rare in cats. These tumors arise from the pancreatic beta cells and produce high levels of insulin. The hallmark of an insulinoma is a normal or elevated blood insulin concentration in the presence of a decreased blood glucose concentration. Insulinomas are most common in middle-aged to older dogs, and large-breed dogs are overrepresented.1 Canine insulinomas are commonly malignant, and metastatic spread is often seen to the regional lymph nodes and liver; metastasis to the lungs is rare.1

CASE PRESENTATION

A 13-year-old castrated male pit bull was referred to the University of Tennessee (UT) Veterinary Medical Center Emergency department for seizure activity secondary to hypoglycemia. The patient had a three-day history of hind end weakness and collapse. An abdominal ultrasonographic examination performed by his referring veterinarian revealed a possible pancreatic mass. At the time of presentation to UT, the patients blood glucose concentration measured too low to read. On physical examination, the patient was laterally recumbent, minimally responsive and had intermittent nystagmus. Emergency treatment included intravenous dextrose, dexamethasone and a glucagon continuous rate infusion (CRI). Frequent feedings were administered once the patient was more alert.

Tumor staging and treatment

The next day, the patient was anesthetized for an abdominal computed tomography (CT) scan, which revealed a 1-cm nodule in the left limb of the pancreas and one mildly enlarged lymph node near the pancreatic body. While the patient was still anesthetized, he was taken to surgery and underwent a partial pancreatectomy and liver biopsy. The mildly enlarged lymph node was not identified at surgery. Postoperatively, the patient had a slow recovery and displayed twitching, jaw clenching and weakness despite a normal blood glucose concentration. There was concern for residual neurologic defects due to a long period of hypoglycemia prior to treatment. The patient slowly improved over five days of hospitalization. He was discharged for monitoring at home, and a low carbohydrate diabetic diet was prescribed. Histopathologic examination of the pancreas revealed an insulinoma with vascular invasion. A liver biopsy showed benign hepatic glycogenation.

Follow-up

The patient was rechecked periodically by his referring veterinarian. He did well clinically and had normal blood glucose concentrations for 10 months. After that time, he developed lethargy and weakness, and had a blood glucose concentration of 60 mg/dl at a recheck. Because of recurrence of signs and hypoglycemia, he was referred to the UT Medical Oncology department for further evaluation. A three-view thoracic and abdominal radiographic examination and ultrasonographic evaluation were performed, which revealed no conclusive evidence of tumor recurrence or metastasis. However, ultrasonographic examination of the abdomen was hampered by gastrointestinal (GI) contents and gas because the patient could not be fasted before the scan due to concern for worsening of clinical signs. Therefore, an abdominal CT scan was recommended to more fully evaluate the abdomen. Prednisone was prescribed at a dose of 0.25 mg/kg twice daily. The patient was discharged from the hospital while additional diagnostic tests were considered by the clients.

That evening, the patient developed an acute onset of seizure activity. He was seen by his referring veterinarian, who documented a blood glucose concentration of 20 mg/dl, and intravenous dextrose and dexamethasone were administered. The patient was transferred back to the UT Emergency department the following day, where additional treatment included a glucagon CRI. An abdominal CT scan was performed, which revealed a new 1.1-cm pancreatic nodule, hepatic nodules and regional lymphadenopathy, consistent with recurrence of the pancreatic tumor and development of metastatic disease. Given the extent of cancer within the abdomen, surgical resection was not possible. Medical management was continued and diazoxide was prescribed. However, due to refractory hypoglycemia despite intensive medical management, the patient was humanely euthanized the next day.

Reference

1. Withrow SJ, Vail DM, Page RL. Tumors of the endocrine system. In: Withrow and MacEwans small animal clinical oncology. 5th ed. St. Louis: Elsevier, 2013.

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