CONDITION

Cushings Disease in Cats

Cushing's disease, also called hyperadrenocorticism, occurs when a cat's adrenal glands produce too much cortisol over a sustained period. Cortisol is a hormone involved in stress response, metabolism, and immune regulation, but in excess it can interfere with many body systems. In cats this condition is uncommon, and when it does occur it is most often seen in middle-aged to older animals, with around four out of five cases also having diabetes mellitus. Owners may notice increased thirst and urination, a larger appetite, a pot-bellied appearance, or skin that seems unusually thin and tears easily during grooming. In cats with diabetes, the pattern that often prompts investigation is insulin that stops working as well as it did, requiring higher and higher doses. Because cortisol interferes with how the body responds to insulin, the two conditions can be closely linked. This page explores what can be observed, what may be happening inside the body, how the condition is investigated through blood tests and imaging, and what approaches exist for managing it. The goal is to help you understand the shape of the condition, not to tell you what your cat has.

Why this matters now

Cushing's disease tends to appear in middle-aged to older cats, most often between the ages of six and fifteen years. It is uncommon in this species, but when it does develop, it arises alongside diabetes mellitus in the large majority of cases—around four out of five affected cats will have both conditions. Cats appear particularly sensitive to the way excess cortisol interferes with insulin's action, which is one reason the two diseases so often travel together.

The condition typically unfolds gradually, over weeks to months. Early changes may be subtle—slight shifts in appetite, a coat that seems less well-kept, or a belly that looks fuller than before. As cortisol levels remain elevated, signs become more pronounced: the skin may begin to thin and tear, muscle mass may diminish despite adequate food intake, and the demands of concurrent diabetes may become harder to meet. The pace varies between individuals, and some cats are recognised only when signs are already well established.

Signals & patterns

Early signals

Increased thirst and urination

A cat may begin drinking more frequently and producing larger volumes of dilute urine. In many cases this reflects concurrent diabetes mellitus rather than the cortisol excess alone, and the two conditions can amplify one another.

Changes in appetite or weight distribution

Some cats develop a noticeably increased appetite, yet their body shape may shift—muscle appears to waste over the spine and shoulders whilst the abdomen becomes rounder or more pendulous. Weight may stay stable, rise, or fall depending on how well diabetes is controlled.

Coat quality decline

The coat may become dull, thin, or unkempt, and a cat that once groomed fastidiously may seem to lose interest or ability. Hair may be easier to pull away, and regrowth after clipping can be slow.

Lethargy or reduced activity

A cat may become quieter, spending more time resting and showing less interest in play or interaction. This can be mistaken for normal ageing, particularly in older individuals.

Later signals

Fragile, tearing skin

The skin becomes paper-thin, shiny, and tears with minimal pressure—even gentle handling or routine blood sampling can cause large wounds that are slow to heal. This is one of the most distinctive features of the condition in cats.

Marked muscle wasting

Muscle loss becomes more obvious, particularly along the spine, shoulders, and hindquarters. The cat may appear frail or weak, with bones more prominent beneath thinned tissue.

Recurrent infections or poor wound healing

The immune system's ability to respond to infection is blunted by chronic cortisol excess, and urinary tract infections or skin wounds may recur or persist despite treatment. Healing is often delayed.

Click to read about the biological mechanisms

How this is usually investigated

Investigation typically begins with a thorough history and physical examination, noting the pattern of signs and whether diabetes is already present or was recently diagnosed. Because Cushing's disease is uncommon in cats and shares features with other conditions, confirmation usually requires several tests, each contributing a piece of the picture. The process often unfolds over days to weeks as results are gathered and interpreted in context.

Physical examination

Purpose: The clinician looks for characteristic changes such as thin, fragile skin that may tear easily, a pot-bellied appearance from muscle wasting and fat redistribution, poor coat quality, and an enlarged liver that may be palpable through the abdominal wall.
Considerations: Many of these signs can appear with other conditions common in older cats, so physical findings alone do not confirm the diagnosis but help shape which tests may be informative.

Blood biochemistry and haematology

Purpose: These tests assess liver enzyme activity, blood glucose, cholesterol, and other markers that tend to be altered when cortisol is elevated. In cats with Cushing's disease, liver enzymes are often not markedly raised (unlike in dogs, because cats lack the steroid-induced alkaline phosphatase isoenzyme), and glucose may be elevated if diabetes is also present.
Considerations: The changes are not unique to Cushing's disease; other conditions can produce similar patterns, so biochemistry usually prompts further specific testing rather than confirming the diagnosis outright.

Low-dose dexamethasone suppression test

Purpose: This test measures how the body responds to a dose of synthetic cortisol. In healthy animals, the dose suppresses natural cortisol production through the normal feedback loop, but in Cushing's disease, cortisol levels remain elevated because the feedback mechanism is disrupted.
Considerations: The test requires blood samples taken over several hours, and interpretation can be complicated in cats with concurrent diabetes or stress, which may also affect cortisol dynamics. False results are possible, so findings are weighed alongside other evidence.

ACTH stimulation test

Purpose: This test measures cortisol levels before and after administration of synthetic adrenocorticotropic hormone. An exaggerated response can suggest that the adrenal glands are overactive, though the pattern differs depending on whether the cause is pituitary or adrenal in origin.
Considerations: The test is less consistently reliable in cats than in dogs, and normal results do not rule out Cushing's disease. It is often used alongside other tests rather than as a single diagnostic tool.

Abdominal ultrasound and advanced imaging

Purpose: Ultrasound allows visualisation of the adrenal glands, which may be enlarged symmetrically if the pituitary is driving excess cortisol production, or asymmetrically if a tumour is present in one gland. Advanced imaging such as CT or MRI can identify pituitary tumours, though these are small and may require specialist equipment.
Considerations: Imaging provides structural information rather than confirming excess cortisol production, so it is most informative when combined with biochemical and functional test results. Not all clinics have access to advanced imaging, and sedation or anaesthesia may be needed.

Options & trade-offs

Management is usually shaped around the individual cat, the severity of signs, the presence of concurrent diabetes, and what the owner finds manageable in daily life. Some approaches focus on reducing cortisol production, while others address the consequences of cortisol excess more directly. Combinations of strategies are common, and what works well for one cat may be less suited to another.

Trilostane

Trilostane is a medication that inhibits an enzyme required for cortisol synthesis, lowering the amount of cortisol the adrenal glands produce. It is given by mouth, typically once or twice daily, and the dose is adjusted based on repeated monitoring of cortisol levels and clinical response. In cats with concurrent diabetes, reducing cortisol can improve blood glucose control, though this may require adjustments to insulin doses.

Trade-offs: The medication requires careful dose titration and regular blood tests to avoid cortisol dropping too low, which can lead to weakness, poor appetite, and potentially serious electrolyte disturbances. Not all cats respond predictably, and some may experience side effects that make the medication unsuitable.

Metyrapone

Metyrapone is another medication that blocks cortisol synthesis, working through a different enzyme pathway than trilostane. It is used less commonly but may be considered when trilostane is not available or not tolerated. Dosing and monitoring requirements are similar, with adjustments based on cortisol levels and clinical signs.

Trade-offs: Experience with metyrapone in cats is more limited than with trilostane, and it may be harder to source. The need for regular monitoring and the possibility of side effects remain, and in some cats the response may be less consistent.

Surgical removal of adrenal tumour

If imaging identifies a single adrenal tumour as the source of cortisol excess, surgical removal can be considered. The procedure is complex, requiring a skilled surgeon and careful perioperative management, but if successful it can resolve the cortisol excess without the need for lifelong medication.

Trade-offs: Surgery carries risks, particularly in older cats or those with concurrent disease, and the adrenal glands are located near major blood vessels, making the operation technically demanding. Not all cats are suitable candidates, and if the tumour is in the pituitary gland rather than the adrenal, surgery is rarely feasible.

Management of concurrent conditions

Because many cats with Cushing's disease also have diabetes mellitus, much of the day-to-day management involves stabilising blood glucose with insulin and dietary adjustments, treating skin infections that arise from fragility and immunosuppression, and supporting overall quality of life. In some cases, particularly when the cat is elderly or frail, this supportive approach forms the main strategy.

Trade-offs: This approach does not reduce cortisol levels, so the underlying metabolic disturbances continue, and signs such as muscle wasting and skin fragility may progress. For some owners and cats, however, the burden of intensive testing and medication may outweigh the benefits of targeting cortisol directly.

Common misconceptions

Misconception:

"If a cat has Cushing's disease, it will always be obvious from their appearance."

Reality:

The signs of Cushing's disease in cats can be subtle, particularly in the early stages, and overlap considerably with other conditions seen in older animals. Some cats develop only mild changes in coat quality or drinking behaviour, and without specific testing, the condition may remain unrecognised for months or longer.

Misconception:

"Cushing's disease and diabetes are the same thing because they both cause increased thirst and urination."

Reality:

While both conditions can produce similar outward signs, they arise from different underlying mechanisms—Cushing's disease involves excess cortisol, while diabetes involves inadequate insulin or insulin resistance. In cats, the two conditions often occur together, and excess cortisol can worsen blood glucose control, but they are distinct processes requiring different approaches.

Misconception:

"Once treatment starts, cortisol levels will return to normal within a few days and all signs will disappear."

Reality:

Adjusting cortisol levels is a gradual process, and finding the right medication dose often takes weeks, with repeated blood tests to guide adjustments. Some changes, such as improved coat quality or reduced thirst, may take longer to become apparent, and certain effects of prolonged cortisol excess, such as muscle loss, may improve only partially even with successful treatment.

Related conditions

Acromegaly in Cats

Acromegaly and Cushing's disease can both occur in middle-aged to older cats and both arise from tumours in the pituitary gland that produce excessive hormones, though acromegaly involves growth hormone whilst Cushing's involves adrenocorticotropic hormone. Both conditions can cause insulin resistance, making concurrent diabetes more difficult to manage.

Pituitary Macroadenoma

In cats with Cushing's disease caused by a pituitary tumour, the growth may occasionally be large enough to qualify as a macroadenoma, which can cause additional signs related to pressure on surrounding brain structures. The distinction between a smaller pituitary adenoma and a macroadenoma is one of size, rather than hormone type, though both may drive excess cortisol production.

Adrenal Tumours

Cushing's disease in cats can arise either from a pituitary tumour that signals the adrenal glands to overproduce cortisol, or from a tumour within the adrenal gland itself that secretes cortisol directly. Distinguishing between these two causes often involves imaging and hormone testing, and the distinction influences which management approaches may be considered.

Diabetic Ketoacidosis

Cats with Cushing's disease often have concurrent diabetes mellitus, and the excess cortisol makes the body more resistant to insulin, sometimes requiring higher doses to maintain control. In cases where diabetes becomes very poorly controlled, ketoacidosis can develop, particularly if the underlying Cushing's disease has not been identified or managed.

Steroid Hepatopathy

Sustained high levels of cortisol, whether from Cushing's disease or long-term corticosteroid medication, can cause a characteristic pattern of change in the liver called steroid hepatopathy. Blood tests in cats with Cushing's disease may show elevated liver enzymes reflecting this hepatic response to chronic cortisol exposure.

Cats with Cushing's disease often live with other conditions that share metabolic or hormonal links, and understanding these connections can be helpful. The Longevity & Healthspan pillar explores how different systems interact as cats age, and how changes in one area may influence another. For cats managing both Cushing's disease and diabetes, patterns of blood glucose control, skin health, and appetite may all shift as treatment progresses, and these are conversations that can unfold over time rather than all at once.