Health Centres - Cushing's syndrome
What is Cushing's syndrome?
Cushing's syndrome describes a cluster of symptoms caused by the effect of excessive steroid hormones, known as glucocorticoids, upon the body.
The production of glucocorticoids, in the form of the hormone cortisol, is a normal function of the adrenal glands. There are two adrenal glands, one on top of each kidney which comprise an inner part (the medulla) and an outer part (the cortex). Each part produces different hormones. Cortisol is produced by the cortex.
The adrenal glands are themselves under hormonal control - from the pituitary gland at the base of the brain. The pituitary produces a hormone called adrenocorticotrophic hormone (ACTH), which stimulates the adrenal cortex to produce cortisol.
The pituitary gland is in turn controlled by the part of the brain immediately above it - the hypothalamus. The hypothalamus produces a hormone called corticotrophin releasing hormone (CRH) which controls the pituitary's function in this regard. Therefore it is a complex system with several steps, and problems can arise from faults occurring at different stages in the control process.
What are the causes of Cushing's syndrome?
The commonest of all causes is the use of steroid medication. Powerful steroids may need to be used for severe asthma and many other conditions, in which case some degree of Cushing's syndrome may have to be accepted. The smallest possible dose that achieves the desired results should always be the aim when using long-term steroid treatment.
Overproduction of cortisol can occur directly from causes within the adrenal cortex, or if there is too much ACTH or too much CRH production.
Cushing's disease is the name given to the rare occurrence of an ACTH-producing tumour within the pituitary gland. ACTH can also be produced in excess by tumours elsewhere in the body - the commonest of these are lung cancers called oat-cell carcinomas or much more benign tumours called bronchial carcinoids.
Finally, temporary overproduction of cortisol may occur in conditions such as alcoholism, depression and anorexia nervosa. This is called pseudo-Cushing's syndrome.
What are the symptoms of Cushing's syndrome?
There are many symptoms of Cushing's syndrome, including the following:
- central obesity, with fat accumulation, particularly around the trunk and between the shoulders, but with thin arms and legs
- purple stretch marks of the skin on the abdomen and breasts
- weight increase
- reduced muscle mass and strength
- headache and back pains
- spots on the face, chest or shoulder, which may be infected
- thirst and increased frequency of passing urine (which may be a sign of high blood sugar levels)
- impotence
- disturbance of periods (less frequent or none)
- osteoporosis (brittle bones)
- hypertension (increased blood pressure)
- growth disturbances in children
- thinning of the skin generally and excessive hairiness
- depression .
How is Cushing's syndrome diagnosed?
A careful history to ensure that steroid medication is not being taken should be done first. Some steroid creams are very potent and can give rise to the condition.
An initial examination and investigation can be performed by a GP, but full investigation is best performed by a specialist in hormone disturbances (endocrinologist).
The diagnosis will be confirmed by performing special urine and blood tests showing high cortisol levels.
Several tests are done to see whether the excess cortisol is of hypothalamic, pituitary, adrenal or 'non-adrenal' origin. For example, the synthetic steroid dexamethasone, when given to a healthy person, will normally 'switch off' cortisol production from the adrenal gland because the pituitary gland recognises dexamethasone as if it were a surge in output of cortisol, in response to which the pituitary production of ACTH falls very quickly. This forms the basis of the 'dexamethasone suppression test'.
Someone who has an adrenal tumour as the cause of their Cushing's syndrome would continue to produce excessive amounts of cortisol in the dexamethasone suppression test, as the tumour would not be responsive to the controlling effect of ACTH.
Further tests would include scans of the pituitary and adrenal glands and lungs to exclude other possible sources of cortisol or ACTH.
Possible complications
-
Diabetes.
-
Hypertension (increased blood pressure).
- Tendency to infections.
- Bone fractures due to osteoporosis and obesity.
- Pituitary gland tumours may enlarge and put pressure on neighbouring parts of the brain.
Treatment
When secondary to steroid treatment the dose of steroid should be reviewed to ensure that it is being used at the minimum effective level.
Cushing's disease is generally treated by surgery to remove the pituitary tumour, and gives a cure rate of over 80 per cent.
Drug therapy can be used to reduce adrenal steroid production if this fails or is unsuitable. The usual medications are metyrapone or ketoconazole (unlicensed use).
Adrenal tumours - both benign and malignant - are treated by surgery. ACTH-producing tumours of the bronchial carcinoid type can be treated by surgery as they are slow-growing but oat-cell cancers of the lung are usually very aggressive, and best treated by chemotherapy.
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