CONDITION
Insulinoma
Insulinoma is a tumour of the pancreas that produces excessive insulin, the hormone that lowers blood glucose. In dogs, these tumours are nearly always malignant, and metastatic spread to lymph nodes or liver is common at the time of diagnosis. The excess insulin causes episodes of low blood sugar, which can affect the brain and nervous system. Owners often notice intermittent signs: sudden weakness, confusion, wobbliness, trembling, or collapse that resolve on their own or after eating. The pattern tends to be episodic because insulin is released in bursts, not continuously. Signs may occur hours after a meal, during exercise, or with no obvious trigger. This page explores what low blood sugar can look like in day-to-day life, how the diagnosis is made, the role of imaging in understanding spread, and the approaches available—including surgery, dietary strategies, and medication—alongside what each may and may not achieve.
Why this matters now
Insulinoma in dogs tends to appear in middle-aged to older animals, with most cases diagnosed between eight and twelve years of age. Certain larger breeds, including Golden Retrievers, Boxers, and Irish Setters, appear over-represented in case series, though the condition can occur in any breed or mixed-breed dog. In cats the condition is rare enough that age and breed patterns are less clear. There are no known dietary, environmental, or lifestyle triggers; the condition arises from spontaneous changes in the insulin-secreting cells of the pancreas.
Most canine insulinomas are malignant, and metastatic spread to the liver, lymph nodes, or other abdominal sites is already present in roughly half of dogs at the time of diagnosis. Despite this, clinical signs are often episodic and intermittent, because insulin release from the tumour occurs in bursts rather than continuously. Between episodes the dog may appear entirely normal, and weeks or months can pass before the pattern becomes clear enough to prompt investigation. Over time, episodes may become more frequent or more pronounced as the tumour burden increases.
Signals & patterns
Early signals
Intermittent weakness or lethargy
The dog may seem unusually tired or reluctant to move for a period of minutes to hours, then recover completely. These episodes often follow exercise or a gap between meals, when glucose demands are higher or stores are lower.
Brief confusion or disorientation
An owner may notice the dog appearing vague, staring into space, or failing to respond to familiar cues. The episode typically resolves on its own, and the dog returns to normal behaviour without intervention.
Wobbliness or unsteady gait
The dog may walk as though slightly drunk, with hind limbs crossing or front legs splaying. This can be subtle and mistaken for joint stiffness or fatigue, particularly in older animals.
Increased appetite or food-seeking
Some dogs become noticeably hungrier or more persistent about scavenging, which may reflect the body's attempt to correct low glucose. This sign is non-specific and easily attributed to other causes.
Later signals
Collapse or loss of consciousness
The dog may suddenly fall or become unresponsive, sometimes with muscle twitching or paddling movements that resemble a seizure. These episodes are typically short-lived, and the dog may recover within minutes, though confusion can linger.
True seizures
In some cases, low glucose triggers generalised seizure activity with loss of consciousness, muscle rigidity, and paddling. Distinguishing these from other causes of seizures requires measurement of glucose at the time of the event, which is rarely possible at home.
Weight gain despite no change in feeding
Chronic excess insulin can promote fat storage, and some dogs gain weight even when their diet remains constant. This is a less common sign and can be overlooked if the dog is otherwise behaving normally between episodes.
Click to read about the biological mechanisms
How this is usually investigated
The episodic nature of signs often means the dog appears entirely normal during a veterinary visit. Diagnosis typically begins with a detailed history, focusing on the pattern and timing of episodes, and progresses to blood testing during or shortly after a symptomatic period. Imaging helps locate the tumour and assess whether spread has occurred, though not all pancreatic tumours are visible on initial scans.
Blood glucose measurement
Paired insulin and glucose sampling
Abdominal ultrasound
Thoracic radiography
Computed tomography
Options & trade-offs
Management usually combines approaches tailored to the individual dog, the extent of disease, and what feels workable for the household. Surgery, dietary adjustment, and medication each address different aspects of the condition, and most dogs receive some combination over time. What suits one family or one stage of disease may not suit another, and the balance often shifts as the condition evolves.
Surgical removal of the tumour
Surgery aims to remove the visible pancreatic mass, and sometimes nearby lymph nodes if they appear involved. In cases where the tumour is confined to one part of the pancreas, partial pancreatectomy can restore more normal insulin regulation for a period. Even when metastatic disease is present, removing the primary tumour can reduce the insulin load and lessen the frequency of hypoglycaemic episodes.
Trade-offs: Surgery carries anaesthetic risk, and the pancreas is a delicate organ; post-operative pancreatitis or temporary diabetes can occur. Not all tumours are fully resectable, and microscopic spread often remains. Survival times vary widely, from months to over a year, depending on the extent of disease at the time of surgery.
Frequent, small meals
Feeding smaller portions more often throughout the day helps maintain steadier blood glucose by providing a regular supply of carbohydrate without large post-meal insulin spikes. Meals that include complex carbohydrates, protein, and fat can slow glucose absorption and reduce the amplitude of glucose swings.
Trade-offs: This approach requires a predictable daily routine and may not fit easily into every household schedule. It can delay or reduce the severity of episodes but does not address the underlying tumour or stop disease progression. Some dogs still experience episodes despite careful feeding, particularly during periods of activity or stress.
Prednisolone
Prednisolone, a corticosteroid, raises blood glucose by promoting gluconeogenesis in the liver and reducing glucose uptake by tissues. It can reduce the frequency and severity of hypoglycaemic episodes, particularly in dogs with inoperable disease or as an adjunct after surgery. Doses are adjusted to the individual response.
Trade-offs: Long-term corticosteroid use can cause increased thirst, urination, appetite, and panting, and may lead to muscle wasting or predispose to urinary infections. Some dogs develop a cushingoid appearance. The drug manages symptoms rather than altering tumour behaviour, and effectiveness may wane over time as tumour burden increases.
Diazoxide
Diazoxide inhibits insulin release from pancreatic beta cells and promotes hepatic glucose release. It is used when dietary management and prednisolone alone are insufficient, or in dogs that do not tolerate corticosteroids well. It is often combined with other measures rather than used in isolation.
Trade-offs: Diazoxide is not licensed for veterinary use in the UK and must be prescribed under the prescribing cascade, which can affect availability and cost. Gastrointestinal upset, lethargy, and rarely bone marrow suppression have been reported. Response varies, and not all dogs achieve adequate glucose control.
Monitoring and adjusting activity
Exercise increases glucose consumption by muscles, which can precipitate hypoglycaemia in a dog with excess insulin. Some owners find that offering a small meal before walks, or adjusting the intensity and duration of activity, reduces the risk of episodes. Observations over time help identify individual triggers.
Trade-offs: This is a practical, low-intervention measure but requires attentiveness and may feel restrictive. It does not replace other management but can complement medical or surgical approaches. The degree of adjustment needed varies, and some dogs remain unpredictable despite careful planning.
Common misconceptions
"Feeding more sugar or sweet treats will prevent low blood sugar episodes."
Giving sugar or high-glycaemic foods causes a rapid spike in blood glucose, which can trigger further insulin release from the tumour and lead to rebound hypoglycaemia within an hour or two. Steady, frequent feeding of balanced meals tends to produce more stable glucose levels than intermittent sugar loads.
"A normal blood test at the vet means the dog does not have insulinoma."
Blood glucose can be entirely normal between episodes, and stress during a veterinary visit may raise glucose temporarily through adrenaline release. Diagnosis often requires repeated sampling, fasting tests, or measurement during a symptomatic period. A single normal result does not exclude the condition.
"Surgery will cure the condition because the tumour has been removed."
Most canine insulinomas are malignant, and microscopic metastatic disease is often present even when imaging appears clear. Surgery can extend symptom-free time and improve quality of life, sometimes substantially, but recurrence or progression of metastatic disease is common over months to years. The procedure is palliative rather than curative in the majority of cases.
Related conditions
Xylitol Toxicity in Dogs
Xylitol toxicity can cause a sudden, severe drop in blood glucose through a similar mechanism—excessive insulin release—though the trigger is ingestion of xylitol rather than a tumour. The acute signs of low blood sugar in xylitol poisoning may resemble the episodic weakness and collapse seen with insulinoma, though the timescale and history differ.
Hepatocellular Carcinoma
Insulinomas in dogs often metastasise to the liver, and imaging may identify nodules that require differentiation from primary liver tumours such as hepatocellular carcinoma. Both can appear as masses on ultrasound or CT, and distinguishing between metastatic insulinoma and a separate primary liver cancer may require biopsy or histopathology.
Chronic Pancreatitis
Both insulinoma and chronic pancreatitis arise in the pancreas, though they affect different cell populations—insulinoma involves the insulin-secreting islet cells, whilst chronic pancreatitis typically involves the exocrine tissue that produces digestive enzymes. In some cases, imaging or bloodwork performed during investigation of one condition may reveal signs of the other.
Brain Tumours
The neurological signs of low blood sugar caused by insulinoma—confusion, wobbliness, altered behaviour, or seizures—can overlap with signs seen in dogs with brain tumours. Distinguishing between the two often depends on measuring blood glucose during an episode and on imaging, as both conditions may present with episodic or progressive changes in mentation or coordination.
Pituitary Macroadenoma
Pituitary macroadenomas can produce neurological signs through mass effect on the brain, whilst insulinomas cause neurological signs indirectly through low blood sugar affecting brain function. Both are hormone-related tumours that may present with episodic or progressive changes in behaviour, coordination, or consciousness, and both may require advanced imaging to identify.
Understanding how insulin and glucose interact throughout the day, and recognising the individual pattern of episodes in your own dog, can help when thinking about what combination of approaches might fit your household. The Longevity & Healthspan pillar explores other conditions affecting older dogs, including those that may coexist with or be mistaken for insulinoma. If your dog has had investigations or a diagnosis, the conversations ahead often centre on staging, prognosis, and what trade-offs feel acceptable at this point in their life.