Insulinoma is a tumor of the pancreas that causes a dog’s body to produce dangerously high levels of insulin, driving blood sugar down to levels that can trigger seizures, collapse, and disorientation. It is the most common insulin-producing tumor in dogs, typically diagnosed around age 10, and it requires prompt treatment to keep blood sugar stable and extend survival.
How Insulinoma Disrupts Blood Sugar
In a healthy dog, the pancreas releases insulin in direct response to blood sugar levels. When blood sugar drops, insulin production slows down automatically. Insulinoma breaks this feedback loop. The tumor’s cells keep pumping out insulin regardless of how low blood sugar falls, creating a state of persistent and sometimes severe hypoglycemia.
This matters because the brain depends almost entirely on glucose for fuel. When blood sugar drops too low, the brain is the first organ to suffer. That’s why the most visible symptoms of insulinoma are neurological: wobbliness, confusion, staring into space, and seizures.
Signs to Watch For
The symptoms of insulinoma can be subtle at first and easy to dismiss as aging. Many owners notice episodes of weakness, trembling, or unusual tiredness that seem to come and go. Dogs may appear disoriented or “spacey,” sometimes stumbling or losing coordination. In more advanced cases, seizures and collapse occur, often after exercise, fasting, or periods without food.
These episodes are typically intermittent. A dog may seem perfectly normal between hypoglycemic dips, which can delay diagnosis by weeks or months. The pattern of symptoms appearing and resolving, especially around meals or activity, is a hallmark clue.
Which Dogs Are Most at Risk
Insulinoma is primarily a disease of middle-aged and older dogs. The median age at diagnosis is 10.4 years, with most dogs falling between roughly 9 and 12 years old, though cases have been documented in dogs as young as 3.
A large UK study identified several breeds with higher-than-average risk: Dogue de Bordeaux, German Pointer, Flat Coated Retriever, Boxer, Hungarian Vizsla, West Highland White Terrier, and English Springer Spaniel. That said, any breed can develop insulinoma, and crossbreeds are among the most commonly diagnosed simply because they make up a large share of the dog population.
How Insulinoma Is Diagnosed
Diagnosis starts with a blood test. The key finding is low blood sugar (below 65 mg/dL) paired with an insulin level that is normal or elevated. In a healthy dog, low blood sugar would cause insulin to drop to near zero. When insulin stays inappropriately high despite low glucose, that combination strongly points to insulinoma.
Sometimes a period of supervised fasting is needed to provoke the blood sugar drop and confirm the pattern. Your vet may run this test in the clinic so the dog can be monitored safely.
Once bloodwork raises suspicion, imaging helps locate the tumor and check for spread. Contrast-enhanced CT scans are the most sensitive tool, detecting primary pancreatic tumors in about 96% of cases. Standard CT without contrast catches roughly 71%, and ultrasound is less reliable than either. CT also helps evaluate whether the cancer has spread to lymph nodes (detected about 67% of the time) or the liver (about 75% sensitivity). These are the two most common sites where insulinoma metastasizes.
Surgery: The Primary Treatment
Surgical removal of the tumor, along with the affected portion of the pancreas, is the standard treatment and offers the best chance at extended survival. The surgeon will also remove any visible metastases found during the procedure.
The survival difference between surgery and medical management alone is significant. In published studies, dogs that underwent surgery had median survival times of 381 to 785 days, compared to 74 to 196 days for dogs managed with medication only. That’s roughly a two- to fourfold difference depending on the study.
Surgery doesn’t cure insulinoma in most cases. The tumor is malignant and has often spread microscopically by the time of diagnosis. But removing the primary mass can dramatically reduce insulin overproduction, giving the dog months or even years of good quality of life before symptoms return.
Medical Management
When surgery isn’t an option, or after surgery when symptoms eventually recur, medical management focuses on keeping blood sugar stable. Veterinarians typically use medications that counteract insulin’s effects or reduce the amount of insulin the tumor releases. Steroids are commonly prescribed because they raise blood sugar by stimulating glucose production in the liver. A second medication may be added that directly inhibits insulin secretion from the tumor cells.
Medical management is a balancing act. Dosages often need adjusting over time as the tumor grows and produces more insulin. Regular blood sugar monitoring and close communication with your vet are essential.
Diet and Feeding Strategy
How you feed your dog matters as much as what medication they’re on. The goal is to provide a steady, slow release of glucose throughout the day rather than big spikes that trigger a surge of insulin from the tumor.
Small, frequent meals (typically four to six per day) are the foundation. Each smaller meal delivers less glucose at once, which means less stimulation of the tumor to release insulin. High-fiber veterinary diets designed for diabetic dogs work well here because they slow glucose absorption from the gut. Avoid treats or foods high in simple sugars, which cause rapid blood sugar spikes followed by rebound crashes.
Exercise should be moderate and consistent. Intense activity burns through glucose quickly and can trigger a hypoglycemic episode. Short, gentle walks after meals are safer than vigorous play on an empty stomach.
What to Do During a Hypoglycemic Episode
If your dog becomes wobbly, disoriented, or starts seizing at home, you can rub corn syrup, honey, or glucose syrup directly onto the gums and inner cheek. You don’t need to get the dog to swallow. The sugar absorbs through the mouth’s tissues. Once the dog is alert enough to swallow safely, offer a small amount of the same syrup by mouth, then seek veterinary care immediately.
Never try to pour liquid into the mouth of a seizing or unconscious dog. Rubbing it on the gums is both effective and safe. Keep a bottle of corn syrup or honey accessible at all times once your dog has been diagnosed.
Long-Term Outlook
Insulinoma is a malignant cancer, and long-term prognosis depends heavily on whether the tumor has already spread at the time of diagnosis and how the dog responds to treatment. Dogs with localized tumors that are surgically removed can do well for one to two years or longer. Dogs with metastatic disease at diagnosis have shorter survival times, though medical management can still provide meaningful months of comfortable life.
The staging of the disease, based on whether the tumor is confined to the pancreas, has reached nearby lymph nodes, or has spread to distant organs like the liver, is one of the strongest predictors of outcome. Your veterinarian or veterinary oncologist can help you understand your dog’s specific stage and what to expect going forward.