Dr Jonathan Tobias
Consultant Senior Lecturer in Rheumatology, Bristol Royal Infirmary

Dr Nimesh Dayal
Specialist Registrar in Rheumatology, Bristol Royal Infirmary

Osteoporosis is the most common bone disease, affecting one in three women and one in twelve men. In this condition, the skeleton gradually loses bone material with increasing age, leading to an increase in its fragility. As a consequence, patients suffering from osteoporosis may break a bone after a relatively trivial injury or even spontaneously. Though there is an increase in risk of a fracture anywhere, the hip, spine and wrist are most commonly affected. Each year in Britain, there are around 60,000 hip, 40,000 spine and 50,000 wrist fractures, osteoporosis being an important underlying cause in many of these cases.

Patients with disorders of the pituitary may be at particular risk of osteoporosis. One of the commonest reasons is that the pituitary produces Gonadotrophins which regulate production of Sex hormones by the ovary and testes. Pituitary disorders can be associated with deficient gonadotrophin production, leading to sex hormone deficiency. Deficiency of sex hormones from any cause is known to lead to premature bone loss and predispose to osteoporosis, in both men and women.

There are several other circumstances in which pituitary disorders may predispose to osteoporosis. For example, low levels of Growth hormone, which occur in a significant proportion of patients with pituitary disorders, have also been shown to be associated with osteoporosis. This may reflect the fact that growth hormone provides an important stimulus for osteoblasts, the cells responsible for laying down bone. In addition, the pituitary has an important function in the regulation of the body's production of steroids by the Adrenal glands. In Cushing's disease, abnormally large amounts of steroids are produced by the pituitary, which causes accelerated bone loss and fractures.

Osteoporosis often goes unnoticed in the early stages, as it does not cause any problem until after a fracture has occurred. Though conventional X-rays can be used to tell if a patient has thinning of the bones suggestive of early osteoporosis, this method is relatively inaccurate. However, newer techniques are now available which are specifically designed to detect bone loss. One of the most commonly used method is a special type of x-ray called a dual energy x-ray absorptiometry (DXA) scan, which measures bone mineral density at the spine and the femur. This is a very simple test using extremely low levels of radiation. It is available at many hospitals, takes only a few minutes to do, and can be very useful in determining to what extent a given individual is likely to develop osteoporosis.

While DXA scans of the spine and hip are thought to be the most accurate way of assessing osteoporosis risk, other methods have been developed which are more portable and easier to use. For example, smaller DXA scanners have been produced which measure bone density at the forearm and ankle. In addition, specific ultrasound machines have been developed for assessing bone strength at the ankle and other sites. Blood and urine tests have also been developed for measuring the rate of bone breakdown, which may also provide useful information about an individual's risk of developing osteoporosis. Though these newer methods of diagnosing osteoporosis are still being evaluated, if proven, they offer the potential for wider access of patients to osteoporosis risk assessment.

Therefore, with the increased choice and availability of methods for diagnosing osteoporosis, there are now good opportunities for patients to have their risk of osteoporosis assessed in detail. One of the main reasons for trying to identify patients with pituitary disorders who are likely to go on and develop osteoporosis is that new drugs have recently become available which are highly effective at preventing further loss of bone. If an individual is found to be at increased risk of osteoporosis, several options are available according to how great this risk is. In relatively low risk patients, simple lifestyle changes may suffice, such as ensuring a good dietary intake of calcium.

For patients at high risk of osteoporosis, specific drug therapy should be given to prevent further bone loss and reduce fracture risk. In the case of patients with sex hormone deficiency, hormone replacement therapy (HRT) may be considered for men as well as women. Several different types of HRT are available, and it is usually possible to find a regime that is well tolerated, though it may be necessary to try several different types of HRT in the process.

Other types of drugs which are effective in treating osteoporosis include bisphosphonates such as alendronate and risedronate, and Oestrogen-like agents like raloxifene.

Patients with pituitary disorders may be at increased risk of developing osteoporosis in later life. However, new tests have been developed for detecting osteoporosis, and effective drugs are available which can prevent its progression. Protecting the skeleton should be considered an integral component of looking after patients with pituitary disorders.

More information about osteoporosis can be found on the website of the National Osteoporosis Society at www.nos.org.uk.