Acromegaly in Cats: The Growth Hormone Disorder Behind Diabetic Resistance
Managing a diabetic cat is already demanding. Twice-daily insulin injections, careful diet, regular glucose monitoring — owners commit to all of it. So when the insulin simply stops working, or when the doses required keep climbing with no improvement in control, the frustration is considerable. In many of these cases, the real problem is not the diabetes itself but a separate hormonal disorder called acromegaly that has been driving insulin resistance from the start.
Understanding Acromegaly
Acromegaly is caused by the chronic overproduction of growth hormone, most commonly from a tumour of the pituitary gland at the base of the brain. Growth hormone has wide-ranging effects on the body, stimulating tissue growth, altering metabolism, and crucially, antagonising the effects of insulin. When growth hormone is chronically elevated, cells become progressively resistant to insulin's signals. The pancreas struggles to compensate, and diabetes follows.
In dogs, excess growth hormone more commonly originates from the mammary glands under the influence of progesterone, particularly in entire females. In cats, the source is almost always a pituitary tumour, and the condition is far more common than previously appreciated. Some studies suggest that acromegaly may be responsible for a significant proportion — estimates range from around 25 to 35 per cent — of poorly controlled feline diabetics.
Who Gets Acromegaly?
The typical patient is a middle-aged to older neutered male cat, though females are also affected. There is no strong breed predisposition. Because the signs develop gradually and the most obvious early feature is uncontrolled diabetes, many cats carry the diagnosis of simple diabetes for months or years before acromegaly is suspected.
The pituitary tumours involved are usually slowly growing adenomas. While they are generally not immediately life-threatening in the early stages, they do enlarge over time, and neurological complications can develop as the tumour presses on surrounding brain structures.
Signs Beyond Uncontrolled Diabetes
The hallmark feature that should prompt suspicion is diabetes that simply cannot be controlled with insulin, regardless of dose adjustments. Some acromegalic cats require doses of insulin far beyond what a diabetic cat would typically need, yet remain persistently hyperglycaemic.
Beyond the diabetes, the effects of chronically elevated growth hormone produce characteristic physical changes over time. These include:
- Increased body size and weight, often despite the metabolic effects of diabetes
- Enlargement of the head and paws, giving the face a broader, coarser appearance
- Prognathism, where the lower jaw protrudes noticeably
- Increased interdental spacing as the jaw bones enlarge
- Organomegaly, including enlarged heart, kidneys, and liver
- Thickening and wrinkling of the skin
- Polydipsia and polyuria consistent with uncontrolled diabetes
Neurological signs such as behavioural changes, circling, or seizures may appear as the pituitary tumour grows, though these are often later-stage developments.
Making the Diagnosis
Acromegaly should be considered in any diabetic cat requiring unusually high insulin doses or showing poor glycaemic control despite appropriate management. A combination of tests is used to confirm it.
Insulin-like growth factor 1, or IGF-1, is the primary screening test. IGF-1 is produced by the liver in response to growth hormone, and elevated levels strongly suggest acromegaly. It is worth noting that IGF-1 can be mildly elevated in cats on high-protein diets, so results need to be interpreted in clinical context.
Advanced imaging — MRI of the brain — is the definitive way to identify the pituitary tumour. CT scanning is an alternative where MRI is not available. Imaging confirms the diagnosis and also provides information about tumour size and location, which is essential for treatment planning.
Why Early Diagnosis Matters
Identifying acromegaly early prevents cats and their owners from enduring months or years of futile attempts to control diabetes through ever-increasing insulin doses. It also allows treatment to begin before the tumour enlarges significantly and before secondary complications such as hypertrophic cardiomyopathy, arthritis from bone changes, or renal failure become well established.
Cardiac involvement is particularly worth noting. Growth hormone has direct effects on the heart muscle, and many acromegalic cats develop hypertrophic cardiomyopathy. Echocardiographic assessment is worthwhile in confirmed cases.
Treatment Approaches
Treatment of feline acromegaly centres on addressing the pituitary tumour. Three main options exist, each with different practical considerations.
Radiation Therapy
Stereotactic radiotherapy, where available, is increasingly the treatment of choice. Targeted radiation can reduce tumour size and lower growth hormone production, often leading to improved diabetic control and, in some cases, diabetic remission. Results vary, and access to specialist radiation centres is limited in many regions, but outcomes in treated cats can be very good.
Surgical Hypophysectomy
Surgical removal of the pituitary gland is performed at a small number of specialist centres and can produce excellent results, including diabetic remission in a proportion of cats. It carries significant surgical risk and requires intensive post-operative management, but for appropriate candidates it offers the potential for long-term resolution.
Medical Management
Where radiation and surgery are not available or not appropriate, medical management focuses on optimising diabetic control as best as possible. Pasireotide, a somatostatin analogue that suppresses growth hormone release, has shown benefit in some cases. The cost and availability of this medication can be limiting factors.
Living With an Acromegalic Cat
Owners who receive this diagnosis after months of struggling with insulin management often feel a mixture of relief at finally having an explanation and concern about what comes next. The honest picture is that this is a manageable condition in many cats, particularly with access to radiation therapy. Quality of life can remain good for extended periods with appropriate care and monitoring.
If your diabetic cat is not responding to insulin as expected, or if you have noticed any physical changes to the face, paws, or body size, raise acromegaly specifically with your vet. An IGF-1 measurement is a straightforward starting point that could fundamentally change the direction of your cat's care.