Iatrogenic Cushing’s syndrome
Most cases of Cushing’s syndrome are related to the use of corticosteroid medication.
Corticosteroids have two main uses. They:
- reduce inflammation in the body; this can be useful for treating conditions such as asthma, and skin conditions such as atopic eczema
- suppress the immune system, which can be useful for treating conditions, such as rheumatoid arthritis and lupus, where the immune system mistakenly attacks healthy tissue
Corticosteroids are available in a number of different forms, including tablets (oral corticosteroids), sprays and inhalers (inhaled corticosteroids), creams and lotions (topical corticosteroids) and injections.
To help prevent side effects, corticosteroids are usually prescribed at the lowest possible effective dose. However, in people with severe symptoms that fail to respond to other forms of treatment, the only effective alternative is to prescribe a long-term course of high-dose corticosteroids.
Corticosteroids contain a synthetic version of the cortisol hormone, so cortisol levels can build up over time, triggering Cushing’s syndrome. People who misuse corticosteroids or take a higher than recommended dose are also at risk of developing Cushing’s syndrome.
The risk of developing Cushing’s syndrome is higher in people who take oral corticosteroids, although the condition can also affect those who misuse inhaled or topical corticosteroids.
Endogenous Cushing’s syndrome
Endogenous Cushing’s syndrome is much less common than iatrogenic Cushing’s syndrome. It's caused by your body producing more cortisol than you actually need.
The most common cause of endogenous Cushing’s syndrome is a tumour (an abnormal growth of cells) which develops in the pituitary gland.
The pituitary gland is a pea-sized gland in your brain. It doesn't produce cortisol, it produces another hormone called adrenocorticotropin hormone (ACTH). ACTH stimulates two small organs that lie above the kidneys, known as the adrenal glands. The adrenal glands release cortisol into the blood.
The tumour can disrupt the normal workings of your pituitary gland so that it produces excessive levels of ACTH, which cause the adrenal glands to produce too much cortisol.
This type of endogenous Cushing’s syndrome is known as Cushing's disease. It's responsible for 70% of all endogenous cases and it's five times more likely to develop in women than in men.
A less common cause of endogenous Cushing’s syndrome is where a tumour develops inside one of the adrenal glands. This accounts for around 1 in 10 cases of the condition.
Another less common cause is known as ectopic ACTH syndrome. This is where a tumour develops inside the lung and starts to produce the ACTH hormone. This type of Cushing’s syndrome is more common in men.
Tumours that develop inside the pituitary or adrenal gland are usually non-cancerous. Other than the symptoms of Cushing’s syndrome, they don't usually pose a serious threat to health. Tumours that develop inside the lung can sometimes be cancerous. It's unclear why these tumours develop.
See the Health A-Z topic about Lung cancer for more information.
