Far Less Common Than in Dogs, But Not to Be Overlooked
Cushing's disease — the common name for hyperadrenocorticism — is caused by chronically elevated cortisol levels in the body. In dogs, it is one of the most frequently diagnosed hormonal conditions. In cats, it is genuinely rare, but that rarity should not translate into dismissal. When it does occur, it tends to present in a distinct and clinically significant way, and it is almost always accompanied by diabetes mellitus that is difficult to control.
Cortisol, produced by the adrenal glands under direction from the pituitary gland, is a steroid hormone essential for managing stress, regulating blood sugar, modulating the immune system, and maintaining blood pressure. When something drives cortisol production into sustained excess, the consequences cascade through every major body system.
Why It Happens in Cats
As in dogs, there are two primary forms. Pituitary-dependent hyperadrenocorticism (PDH) accounts for approximately eighty per cent of feline cases and results from a tumour in the pituitary gland that overproduces adrenocorticotropic hormone (ACTH), which in turn drives both adrenal glands to produce excess cortisol. Adrenal-dependent hyperadrenocorticism accounts for the remaining cases and involves a tumour in one or both adrenal glands producing cortisol autonomously.
Iatrogenic Cushing's — caused by prolonged administration of corticosteroid medications — is the third category and occurs in cats just as it does in other species. This form resolves with careful dose tapering of the offending medication, though this must be done slowly and under veterinary supervision to avoid adrenal crisis.
Most affected cats are middle-aged to old, with a slight over-representation of females in some case series. No breed appears dramatically over-represented, though Domestic Shorthairs feature prominently in published case reports.
The Signs Are Different to Those in Dogs
Experienced dog owners or veterinary staff familiar with canine Cushing's should be aware that feline hyperadrenocorticism often looks different. The classic signs in dogs — pot-bellied appearance, hair loss on the flanks, excessive drinking — certainly occur in cats too, but the presentation is frequently dominated by skin fragility that has no real equivalent in canine disease.
Characteristic signs in cats include:
- Skin that tears or bruises extraordinarily easily — this is called feline skin fragility syndrome and can be so severe that handling the cat causes wounds
- A pot-bellied, pendulous abdomen due to muscle wasting and abdominal fat redistribution
- Symmetrical hair loss over the trunk
- Thin, paper-like skin that heals poorly
- Lethargy and generalised weakness
- Markedly increased thirst and urination
- Increased appetite
- Concurrent diabetes mellitus that is insulin-resistant
The skin fragility seen in feline Cushing's can be striking and alarming. Cats may develop large wounds or skin tears from minimal trauma, and surgical procedures carry significantly elevated anaesthetic and wound-healing risks.
Diagnosing Cushing's in Cats
Diagnosis is more challenging in cats than in dogs because the standard screening tests validated for canine Cushing's do not translate reliably. The urine cortisol to creatinine ratio is used as a screening test but has poor specificity in cats, meaning many positive results are false. The low-dose dexamethasone suppression test is the most commonly used confirmatory test in cats, though interpretation requires care and experience.
ACTH stimulation testing, widely used in dogs, has limited utility in feline Cushing's as many affected cats do not show an exaggerated response, making it less sensitive for diagnosis in this species.
Once biochemical evidence of hypercortisolism is established, imaging of the adrenal glands and pituitary is performed. Abdominal ultrasound can identify adrenal enlargement or asymmetry. CT or MRI of the pituitary provides the most detail for surgical or radiotherapy planning.
Treatment Options for Affected Cats
Trilostane
Trilostane inhibits an enzyme required for cortisol synthesis and is the most widely used medical treatment for feline hyperadrenocorticism. It requires careful dose titration and monitoring, as suppression of cortisol that goes too far can cause an Addisonian crisis — a life-threatening lack of adrenal hormones. Cats on trilostane need regular ACTH stimulation testing to guide dosing and regular clinical review.
Surgical Adrenalectomy
In cats with adrenal-dependent Cushing's, removal of the affected adrenal gland offers the possibility of cure. The surgery is high-risk in Cushing's cats due to their skin fragility, immunosuppression, poor wound healing, and concurrent diabetes. Nonetheless, in cats who are stabilised pre-operatively and operated on by experienced surgeons, outcomes can be good.
Radiation Therapy
For pituitary-dependent disease, radiation targeting the pituitary tumour has been used in specialist centres. Results in cats are less extensively reported than in dogs, but the principle — reducing ACTH output by damaging the tumour — is sound, and clinical improvement has been documented.
The Diabetes Connection
The vast majority of cats with Cushing's disease have concurrent diabetes mellitus. Cortisol is profoundly anti-insulin in its effects, promoting glucose production in the liver and reducing insulin sensitivity in peripheral tissues. As a result, diabetic cats with Cushing's typically require very high insulin doses and remain in poor glycaemic control until the cortisol excess is addressed.
Interestingly, when Cushing's is successfully treated, some cats experience diabetic remission as insulin sensitivity is restored. This underscores the importance of pursuing a diagnosis in any diabetic cat with atypical features — particularly skin fragility, unusual weight distribution, or extreme insulin resistance.
Prognosis and Quality of Life
The prognosis for feline Cushing's is guarded. Skin fragility makes these cats vulnerable to serious infections and wound complications. The concurrent diabetes adds management complexity. Pituitary tumours can grow and compress surrounding brain tissue over time. Despite this, cats whose disease is identified and treated appropriately can achieve periods of meaningful quality of life, and some do considerably better than the initial diagnosis might suggest.
Owners of affected cats benefit enormously from working with a veterinary internist or specialist, given the complexity of concurrent disease management and the risks associated with each treatment approach. As with most hormonal conditions in cats, the trajectory of the disease is shaped significantly by how promptly diagnosis is made and how consistently management is pursued.