By Dial A Vet Veterinary Team
Last updated: 2 November 2026
An older dog who suddenly goes wobbly on a walk, trembles or has a seizure, then seems almost normal again a little later, can leave owners confused and worried. One cause of this pattern is an insulinoma, a tumour of the pancreas that releases too much insulin and drives blood sugar dangerously low. Insulinomas are uncommon, but they are serious, and repeated or prolonged low blood sugar can harm the brain. Knowing the signs helps you get help early.
Key takeaways
- An insulinoma is a tumour of the insulin-producing cells of the pancreas. It is the most common pancreatic tumour in dogs.
- Too much insulin causes hypoglycaemia (low blood sugar), which mainly affects the brain.
- Common signs are seizures, weakness, hind leg weakness, collapse and muscle twitching. Episodes often come and go.
- Episodes can be triggered by exercise, fasting, excitement or stress, and sometimes by eating.
- A seizure or collapse is an emergency. See a vet immediately.
- Surgery usually gives the longest survival, but most insulinomas in dogs have spread by the time they are found, so many dogs need ongoing medical and dietary management.
What is an insulinoma?
Insulin is the hormone that moves sugar (glucose) out of the blood and into the body's cells. The brain relies heavily on glucose for energy. An insulinoma is a tumour arising from the beta cells of the pancreas, which make insulin. The tumour keeps releasing insulin even when blood sugar is already low.
The Merck Veterinary Manual notes that insulinomas are considered malignant in dogs because they almost always spread beyond the pancreas. In 40 to 50% of dogs, the tumour has already spread to nearby lymph nodes or the liver before diagnosis.
Which dogs are affected?
Insulinomas are seen mainly in middle-aged and older dogs. Merck reports a median age of 10 years, with a range of 3 to 16 years. A 2022 review by Dr Floryne Buishand of the Royal Veterinary College notes that middle-sized to large breeds are most often diagnosed. There is no sex predisposition and no clear breed predisposition, although more cases appear in breeds such as German Shepherds, Irish Setters, Boxers, Golden Retrievers, Poodles, Fox Terriers, Collies and Labrador Retrievers. The cause is not known.
Signs of insulinoma in dogs
In a combined group of 320 dogs reported in the review, the most common signs were:
- Seizures (about half of dogs)
- Generalised weakness
- Weakness of the hind legs
- Collapse
- Muscle twitching or trembling
- Wobbliness or poor coordination
Some dogs also seem nervous, restless or unusually hungry, or drink and urinate more. Merck notes that signs are typically episodic. At first, episodes are spaced far apart, but they become more frequent and longer as the disease progresses. Because the signs are mainly neurological, insulinoma can be mistaken for epilepsy or a brain tumour.
When to see a vet
Go to your nearest vet clinic immediately if your dog:
- Is having a seizure, or has had more than one
- Collapses or cannot stand
- Is confused, unresponsive or very weak
The review stresses that a hypoglycaemic crisis should be treated straight away, because the shorter the period of low blood sugar, the lower the risk of permanent brain damage. Do not put anything in the mouth of a dog that is seizing or not fully alert. Phone the clinic on the way so they can prepare.
Book a prompt appointment if your older dog has short, unexplained spells of weakness, trembling or wobbliness, especially after exercise or a missed meal, even if they recover quickly.
If your dog has already been diagnosed, ask your vet for a written plan covering what to do during an episode.
How vets diagnose insulinoma
Merck advises that blood glucose should be measured in any older dog with a history of periodic weakness, collapse or seizures. The key finding is low blood sugar at the same time as a normal or high insulin level. If your dog's blood sugar is normal at the visit, your vet may carefully withhold food in hospital with frequent glucose checks, because levels can drop quickly.
Your vet will also look for other causes of low blood sugar, such as Addison's disease, liver failure, other large tumours and sepsis. Imaging is used to find the tumour and check for spread. Both sources note that contrast CT is the preferred scan, because ultrasound misses many insulinomas.
Treatment
Emergency care. A dog in a hypoglycaemic crisis is given glucose into a vein in hospital and closely monitored.
Surgery. Merck describes surgery as generally the best option to control signs and improve survival, especially when there is a single tumour that has not spread. The surgeon removes the tumour and any visibly affected lymph nodes. If spread cannot be seen or removed, low blood sugar may continue after surgery. Some dogs have high blood sugar after surgery, and a few go on to develop lasting diabetes.
Medical and home management. Dogs that are not surgical candidates, or whose signs return, are managed with:
- Four to six small meals a day of a diet high in protein, fat and complex carbohydrates, avoiding sugary foods that trigger insulin release
- Exercise limited to short lead walks
- Prescription medicines that raise blood sugar or reduce insulin release, chosen and adjusted by your vet
Some dogs may also be offered chemotherapy or newer targeted cancer drugs. Your vet or a veterinary oncologist can explain whether these are suitable.
Outlook
The outlook is guarded, because low blood sugar almost always returns as the tumour regrows or spreads. The review reports a median survival of about 14 months after surgery, compared with about 4 months for dogs treated with medicine alone. Merck notes that some dogs live more than 2 years with good quality of life when all visible tumour is removed. Every dog is different, so ask your vet what to expect in your dog's case.
Prevention
There is no known way to prevent insulinoma. The best protection is early detection. Mention any unexplained episodes of weakness, trembling or collapse to your vet, and keep up regular health checks for senior dogs.
FAQ
Is insulinoma the same as diabetes?
No. In diabetes there is too little insulin and blood sugar runs high. With an insulinoma there is too much insulin and blood sugar runs low.
Why did my dog recover after eating?
Food raises blood sugar, so signs can ease after a meal. However, eating can also stimulate the tumour to release more insulin, which is why small frequent meals are advised.
Can insulinoma be cured?
Rarely. Surgery can control signs for a long time, but most dogs eventually need ongoing management.
Can cats get insulinomas?
Merck notes that insulinomas in cats are very rare.
Talk with a vet
If your older dog has had a brief spell of weakness or trembling and you want help deciding what to do next, Dial A Vet's real vets and vet nurses can talk it through with you on a video consult. For a seizure or collapse, go straight to your nearest clinic. More reading: what to do if your dog has a seizure. Book a video consult with Dial A Vet.
References
- Merck Veterinary Manual. Islet Cell Tumors in Dogs and Cats.
- Buishand FO. Current Trends in Diagnosis, Treatment and Prognosis of Canine Insulinoma. Vet Sci. 2022.
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If you are worried about your pet right now, contact your local vet or nearest emergency animal hospital.