Cushing's syndrome

What it is

Cushing's syndrome is a serious hormonal disorder caused by prolonged, excessive exposure to cortisol, affecting an estimated 40 to 70 people per million and women approximately three times as often as men. Also called hypercortisolism, Cushing's syndrome is the broad clinical term for any condition — whether driven by the body itself or by medication — that produces sustained cortisol excess. Most cases are diagnosed in adults between 30 and 50 years old, though the condition can occur at any age, including in children.

A critical distinction for Canadian patients: Cushing's syndrome and Cushing's disease are not interchangeable terms. Cushing's disease is a specific subtype in which a benign pituitary adenoma overproduces adrenocorticotropic hormone (ACTH), which then drives the adrenal glands to produce too much cortisol. Cushing's disease accounts for roughly 70% of endogenous (internally caused) cases. The remaining 30% arise from adrenal tumors or ACTH-secreting tumors elsewhere in the body. Exogenous Cushing's syndrome — caused by long-term corticosteroid medications — is the most common form overall and is frequently encountered in Canadian patients managing asthma, rheumatoid arthritis, or inflammatory bowel disease.

Left untreated, Cushing's syndrome substantially raises the risk of type 2 diabetes, osteoporosis, cardiovascular disease, and serious infections.

Causes and mechanism

Cortisol is produced by the adrenal glands in response to ACTH from the pituitary gland. Normally, a feedback loop keeps cortisol within a healthy range. Cushing's syndrome occurs when that loop breaks down — or is bypassed entirely.

Cause	Mechanism	Share of cases
Cushing's disease (pituitary adenoma)	Benign pituitary tumor overproduces ACTH → adrenal overproduction of cortisol	~70% of endogenous cases
Adrenal tumor (adenoma or carcinoma)	Adrenal gland produces cortisol autonomously, independent of ACTH	~15% of endogenous cases
Ectopic ACTH syndrome	ACTH-secreting tumor outside the pituitary (e.g., small cell lung cancer, carcinoid) drives adrenal overproduction	~10–15% of endogenous cases
Exogenous / iatrogenic	Long-term use of corticosteroids (prednisone, dexamethasone, hydrocortisone) mimics cortisol excess	Most common cause overall

For Canadian patients on long-term steroid therapy, the cumulative dose and duration are the key risk factors. Dose review and monitoring for metabolic effects are part of responsible prescribing under Canadian clinical standards.

Symptoms and diagnosis

Symptoms develop gradually, which is one reason Cushing's syndrome is significantly underdiagnosed. No single feature is pathognomonic, but the combination of several findings together should prompt investigation.

Physical signs include central weight gain with relatively thin limbs, a rounded "moon face," a fatty deposit at the upper back and neck ("buffalo hump"), purple or pink abdominal striae, skin thinning, easy bruising, and slow wound healing. Muscle weakness — particularly difficulty climbing stairs or rising from a chair — is common and often underreported.

Metabolic and systemic effects include hypertension, elevated blood glucose or frank type 2 diabetes, and osteoporosis with vertebral or hip fractures.

Sex-specific features: women may develop hirsutism, menstrual irregularities, or amenorrhea; men may experience reduced libido and erectile dysfunction.

Psychiatric symptoms — depression, anxiety, irritability, cognitive difficulties, and in severe cases psychosis — are well documented and can precede the physical features.

Confirmed diagnosis requires biochemical testing:

1. 24-hour urinary free cortisol — elevated levels are a strong indicator; at least two collections are recommended.
2. Late-night salivary cortisol — cortisol should be at its nadir between midnight and 2 a.m.; elevated levels are a sensitive screening marker. LifeLabs and Dynacare both process this test in Canada.
3. Low-dose dexamethasone suppression test — in healthy individuals, 1 mg of dexamethasone suppresses morning cortisol; failure to suppress suggests Cushing's syndrome.
4. ACTH levels and imaging — once cortisol excess is confirmed, plasma ACTH distinguishes ACTH-dependent from ACTH-independent causes. MRI of the pituitary or CT of the adrenal glands then localizes the source.

Treatment options

Treatment is directed at the underlying cause and aims to normalize cortisol levels.

Surgery is first-line for most forms. Transsphenoidal resection of the pituitary adenoma is the standard approach for Cushing's disease; remission rates reach 65–90% for small, well-localized tumors when performed by an experienced neurosurgeon. Adrenal tumors are typically removed laparoscopically. Recurrence after apparently successful surgery is possible, making long-term cortisol monitoring essential.

Radiation therapy is a second-line option for Cushing's disease when surgery has not achieved remission or is not feasible. Effects on cortisol levels can take months to years to manifest.

Cortisol-lowering medications — including metyrapone, ketoconazole, pasireotide, and mifepristone — are used to control hypercortisolism while awaiting surgery, after incomplete surgical cure, or as long-term management when surgery is not an option. Etomidate is reserved for acute, severe cases requiring rapid cortisol reduction. Availability and coverage of these agents vary by province; patients should confirm formulary status with their provincial drug benefit program.

Bilateral adrenalectomy — removal of both adrenal glands — is considered when other treatments have failed. It requires lifelong glucocorticoid and mineralocorticoid replacement.

Tapering exogenous corticosteroids is the primary strategy for medication-induced Cushing's. Dose reduction must be gradual and supervised; abrupt discontinuation risks adrenal insufficiency.

When to see a clinician in Canada

Seek assessment from a family physician or endocrinologist if you notice several of the following together: unexplained central weight gain with thin limbs, new purple or pink stretch marks on the abdomen or thighs, skin that bruises unusually easily, progressive proximal muscle weakness, blood pressure or blood sugar that is difficult to control, or menstrual irregularities alongside fatigue and weight changes.

In Canada, initial screening (salivary cortisol, urinary free cortisol, or dexamethasone suppression testing) can be ordered by a family physician. Referral to an endocrinologist is typically required for confirmatory testing and imaging. Wait times vary by province; patients in areas with limited specialist access may consider telehealth platforms — such as Maple, Felix, or Cleo — for initial triage, though definitive diagnosis and surgical management require in-person specialist care.

Limitations and open questions

Research is still emerging on the optimal sequencing of cortisol-lowering medications when surgery is not curative, and head-to-head trial data comparing agents like pasireotide and metyrapone remain limited. The long-term cardiovascular and bone-density outcomes after successful treatment are not fully characterized, particularly for patients who had prolonged disease before diagnosis. Health Canada has not issued a dedicated clinical guideline for Cushing's syndrome; Canadian endocrinologists generally follow the Endocrine Society's 2008 diagnostic and 2015 treatment guidelines, adapted to provincial formulary constraints. The prevalence of subclinical or mild hypercortisolism — sometimes called "possible autonomous cortisol secretion" in the context of adrenal incidentalomas — is an area of active investigation, and consensus on when to treat these cases is still evolving.