Cat Acromegaly (Hypersomatotropism): Signs and Diagnosis

Acromegaly — caused by excess growth hormone from a pituitary tumor — is an underdiagnosed but important cause of insulin-resistant diabetes in cats. The physical changes are gradual and easy to miss, but recognizing them early changes treatment planning significantly.

Last reviewed: June 2026

What Is Acromegaly (Hypersomatotropism) in Cats?

Acromegaly, also called hypersomatotropism (HST), results from chronic overproduction of growth hormone (GH) by a functional adenoma of the pituitary gland. In cats, this is almost exclusively a disease of middle-aged to older males, though females can be affected. The excess GH drives overproduction of insulin-like growth factor 1 (IGF-1) from the liver, which promotes abnormal soft tissue and bone growth throughout the body over months to years.

The condition is clinically important primarily because it causes severe, refractory insulin resistance — meaning affected cats develop diabetes mellitus that cannot be controlled with even very high insulin doses. Estimates suggest that acromegaly accounts for 25–35% of cats with poorly regulated or insulin-resistant diabetes, making it far more common than previously appreciated. As described in Ramsey's BSAVA Manual of Small Animal Endocrinology, acromegaly in cats was historically considered rare, but improved awareness and routine IGF-1 testing have revealed a much higher prevalence than expected.

Signs of Acromegaly in Cats

Many signs develop very gradually over months to years and may go unnoticed until the cat is presented for difficult-to-regulate diabetes:

Metabolic signs (often the presenting complaint):

• Poorly controlled or insulin-resistant diabetes — requiring high insulin doses (>15 units per injection) with persistently elevated blood glucose
• Increased appetite — often dramatic, despite diabetes
• Increased thirst and urination — from the diabetes component
• Slow weight gain or maintenance of body weight despite diabetes (this is notable — diabetic cats typically lose weight)

Physical changes from excess growth hormone:

• Gradual enlargement of the head and jaw — the face may appear broader or the jaw more prominent than before
• Enlarged paws — owners may notice the cat seems to have grown
• Wider body frame or increased overall size compared to prior
• Skin changes — thickening of the skin; some cats develop a characteristic "thick-skinned" appearance
• Prognathism — the lower jaw protrudes slightly beyond the upper
• Abdominal enlargement from organ hypertrophy (especially the liver, kidneys, and heart)

Signs from the pituitary tumor itself (in advanced cases):

• Neurological signs — the pituitary tumor can compress adjacent brain structures, causing behavioral changes, circling, seizures, or blindness
• Changes in vision or unusual eye positioning

Any diabetic cat with increased food intake, weight gain instead of weight loss, and very high insulin requirements should be evaluated for acromegaly (AAFP-AAHA Feline Life Stage Guidelines, 2021).

Diagnosis

Screening for acromegaly should be routine in any cat with insulin-resistant diabetes. Diagnosis involves:

• Serum IGF-1 measurement — the most practical screening test; an elevated IGF-1 (typically >1,000 ng/mL in affected cats) is strongly suggestive; a value within the normal reference range makes acromegaly less likely but does not fully exclude it
• Advanced imaging — MRI of the brain and pituitary gland is the definitive diagnostic tool; a pituitary mass is visible in most affected cats, though size varies; CT can also be used
• Full diabetic workup — fructosamine, blood glucose curve, urinalysis, chemistry panel to assess concurrent organ involvement
• Echocardiography — acromegaly causes cardiac hypertrophy similar to HCM, making cardiac assessment important before any anesthetic procedure

Treatment Options

Treatment aims to reduce GH production or its effects, and to control diabetes:

• Radiation therapy — stereotactic radiosurgery (SRS) or conventional radiation to the pituitary tumor is the most effective treatment currently available; some cats achieve diabetic remission after tumor shrinkage; average survival in treated cats can exceed 3 years
• Hypophysectomy (surgical removal of the pituitary) — available at select specialty centers; high technical demands but outcomes are promising in experienced hands
• Medical management — somatostatin analogs (e.g., pasireotide) and dopamine agonists have been investigated but are generally less effective in cats than in humans with acromegaly; cabergoline has shown some benefit in reducing IGF-1 levels
• Insulin management — regardless of other treatment, very high insulin doses (sometimes >30 units twice daily) may be needed to manage blood glucose; close glucose monitoring is essential to avoid dangerous hypoglycemia if tumor treatment succeeds and insulin requirements drop rapidly

As described in Côté's Clinical Veterinary Advisor: Dogs and Cats, cats with untreated acromegaly typically survive 1–2 years from diagnosis, with death often from cardiac failure, diabetic complications, or neurological deterioration from the growing pituitary tumor.

When to See a Vet

Call your vet today if:

• Your diabetic cat requires increasingly large insulin doses to control blood glucose
• Your diabetic cat is gaining weight or maintaining weight instead of losing it
• You notice your cat's face or paws seem larger than they used to be
• Your cat is eating voraciously despite known diabetes

Go to the ER immediately if:

• Your diabetic cat has a seizure, is disoriented, or suddenly loses vision
• Your cat collapses or cannot stand after an insulin injection (possible hypoglycemia)
• Your cat is vomiting and unresponsive — diabetic crisis requires emergency care

Frequently Asked Questions

How common is acromegaly in diabetic cats? Studies suggest acromegaly may be present in 25–35% of cats with insulin-resistant or poorly regulated diabetes — making it a frequent rather than rare finding in that population. Because physical changes are subtle and gradual, many cases go undiagnosed until a clinician specifically screens with an IGF-1 test. Any diabetic cat that is difficult to regulate should have IGF-1 checked.

Can acromegaly cause heart disease in cats? Yes. Excess growth hormone causes cardiac muscle hypertrophy similar to HCM. Cats with acromegaly frequently have concentric left ventricular hypertrophy on echocardiography, which increases risk of congestive heart failure and aortic thromboembolism — the same complications as idiopathic HCM. Pre-treatment cardiac evaluation is important because cardiac status affects anesthetic planning for radiation or surgery.

How much does diagnosing and treating acromegaly cost in cats? IGF-1 blood testing runs $80–150. Pituitary MRI or CT typically costs $1,500–3,000. Stereotactic radiation therapy, where available, generally runs $5,000–10,000 for the full course. Hypophysectomy at specialty centers costs $4,000–8,000. Ongoing insulin management, glucose monitoring supplies, and quarterly bloodwork for a diabetic acromegalic cat typically adds $200–500 per month in ongoing care costs.

What does an acromegalic cat look like compared to a normal diabetic cat? A diabetic cat without acromegaly typically loses weight despite eating well. An acromegalic diabetic cat often eats heavily and maintains or even gains weight. Physically, the face may be slightly broader or the jaw more prominent, the paws may appear enlarged, and the overall frame may look bigger than before. These changes are subtle and build over months, which is why comparison to old photos can be very helpful at the vet visit.

Is acromegaly in cats the same as in dogs? No — the causes differ significantly. Feline acromegaly is caused by a pituitary adenoma secreting excess GH. In dogs, acromegaly historically occurred primarily in intact females as a result of progesterone stimulating GH production from mammary gland tissue; pituitary-origin GH excess is much less common in dogs. Spaying intact female dogs resolves the most common canine form, whereas feline acromegaly requires pituitary-directed treatment.

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