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Osteoporosis Explained


Healthy bones are important for good health. As discussed in the last issue, bones give not only structural strength and a rigid framework for our body but also provide for attachment of muscles so that movements of our body are possible. Further, bones act as a reservoir of calcium and phosphate. They also enclose bone marrow which has many vital functions including production of cells of the blood and bones also provide protection to vital organs such as the brain, heart, lungs, etc.

It is a surprise to many people to learn that bone is a dynamic structure undergoing constant remodelling throughout life. The two main types of bone are compact bone and cancellous bone. Compact bone gives mechanical strength and offers protection from injury while the looser cancellous bone acts as the main site for storage of and exchange of minerals like calcium and phosphorus with the rest of the body.

Bone is composed of a matrix of organic (mainly protein) and inorganic (the minerals - calcium and phosphate) components along with cells. Amongst the important cells of bone are osteocytes, osteoblasts and osteoclasts. Osteoblasts mainly active in laying down bone while osteoclast activity is predominantly related to resorption of bone.

Osteoporosis is a very widely prevalent disorder in which the bone mass is reduced along with deterioration of its micro-architecture. This results in increased fragility of bone and fractures with even trivial trauma. It is much commoner in Caucasian and Asian women and especially so after stoppage of menopause around 45 to 50 years of age.

Most people with osteoporosis are not aware of its presence till they suffer fractures often after trifling falls or injuries. The hip, the wrist and vertebrae (the spine) are favoured spots for osteoporosis related fractures. Osteoporosis is also responsible for the decrease in height and the stooping of old age.

Diagnosis depends almost wholly on imaging methods. Laboratory tests including measurements of calcium and phosphorus levels in blood are often normal. The enzymes that measure bone turnover maybe raised at times of high activity in bones for example following a fracture. However, they are often normal in other cases and are not too sensitive in diagnosing osteoporosis.

Amongst the imaging tests available, the simplest and most readily available is an X-ray. The site from which symptoms are originating is the one usually X-rayed while in patients in whom it is done for screening purposes, the spine is the best site. Low bone density on an X-ray suggests osteoporosis. However, this is not appreciable till almost 30 per cent of bone mineral is lost and is obviously not going to be of use in picking up early osteoporosis. Further, if the exposure of the X-ray is not proper, it is very easy to both miss the diagnosis or to wrongly diagnose osteoporosis.

Bone mineral density measurement is much more reliable in predicting the risk of fracture. Bone densitometry is reported as a T-score which compares the density of the bone of the tested individual against a healthy young adult. If the score is within one standard deviation, a commonly used statistical parameter, of the normal value as per WHO guidelines, her bones are considered to be having normal density. If the value is between -1 and -2.5 standard deviation of this normal, the bone density is considered as deficient but not frank osteoporosis which is diagnosed when the value is below 2.5 standard deviations.

A confounding factor can be difference in bone density in different bones. Especially when following up a patient, the bone densitometry reading is always therefore desirable for the same site.

The measurement of bone density is carried out by what is called DXA scan or a quantitative CT scan can be used. DXA scan is the usually utilized method since it is less expensive and also the patient is subjected to less radiation. Since osteoporosis is so common, estimated to affect maybe a third of women and one in eight men it becomes a debatable point as to who should go for this test. It is obviously not practical or economically viable for the entire population to undergo this test. Basically all women over 65 years of age and those below 65 years but having risk factors or those who have been on hormone replacement therapy for long periods as well as persons of both sex with unexplained bony symptoms or fractures are considered as candidates for this test.

Prevention is generally the best treatment and this holds good in osteoporosis too. Adequate dietary intake of calcium and vitamin D is considered desirable. Whether this in fact prevents osteoporosis is not too certain with different studies giving differing results. These nutrients are probably most helpful in deficient individuals but unlikely to be too useful in other individuals in preventing or treating osteoporosis. A minimum intake of 1 gramme calcium is considered advisable in all adults with the recommendation rising to 1.5 gramme in persons at risk of osteoporosis such as women after menopause. For vitamin D, the usual recommended intake is between 400 to 800 units.

Weight bearing exercise for thirty minutes at least three times a week is also believed to be helpful in osteoporosis prevention. This sort of exercise is recommended throughout life rather than only after menopause ceases.

Smoking is a significant factor in enhancing bone loss and this obviously needs to be avoided. This is important not only from the point of view of healthy bones but also prevention of heart disease, lung cancer, emphysema, chronic bronchitis, etc.

Use of steroids is another major risk factor for osteoporosis. Since steroids, especially for long-term use, are recommended only for significant medical disease and that also when there are no safer options it is very difficult to avoid them. However, taking the least possible dose is something that both patient and doctor have to strive for.

Amongst the treatment modalities, one of the most commonly used is Hormonal Replacement Therapy known by its acronym as HRT. The hormones from the ovaries which become deficient in the body after onset of menopause are replaced by oral pills of these hormones or their synthetic analogues. Oestrogen is the important hormone as far as the bones are concerned. HRT is quite effective in preventing osteoporosis but expectedly the effect is lost once tablets are discontinued. Further, since long-term use of these hormones is itself not free from risk it is not the ideal treatment except in persons with significant symptoms or risk and in them also the decision on how long to continue the drug is a debatable one.

Raloxifene is a drug which modulates the effect of oestrogen in bones without modulating the oestrogen receptors in the uterus. In effect, it is a selective modulator of oestrogen response acting on these receptors in the bones. The advantage is that the desired effect on the bones is achieved whilst avoiding the undesirable effects on the uterus.

Biphosphonates are the second group of drugs found to be effective in treating osteoporosis. Alendronate was the first drug to be introduced in this class but subsequently a number of other related molecules have been approved by medical authorities. They are fairly safe though some patients find difficulty in tolerating them because of acidity disorders affecting the food-pipe and stomach. Again, the problem of how long a person with osteoporosis or at risk of this disease needs to take them is disputed. Logically the drug would need to be taken life long since the bones again start losing mass when the drug is stopped.

While female hormones are given as HRT, the male hormone (testosterone) can also be utilised. These are by and large used only in men with osteoporosis or at risk for this problem. Again, long-term use has its own risks and complications.

All the above forms of therapy act by reducing bone resorption rather than by promoting formation of new bone. Thus, only one part of the problem is tackled. Some newer therapies offer hope of better results by targeting the promotion of new bone formation. Amongst them is a hormone called Parathormone, also know as PTH. This is normally produced by the parathyroid glands which are located close to the thyroid gland in the neck. PTH regulates calcium and phosphate metabolism in the body and a synthetic derivative has found good results in trials.

Calcitonin is another hormone that has been found to be of use in osteoporosis, this time however reducing bone resorption rather than promoting new bone formation.

Fluoride has also been suggested as a potential agent for treating osteoporosis as it promotes bone formation. However, there are concerns about its safety as well as the quality of new bone formed and is currently not recommended for treating osteoporosis.

Any fractures or deformities occurring as a result of osteoporosis merit prompt attention to ameliorate their effects on the quality of life and mobility of these often elderly individuals with usually a number of other old-age related diseases.

Courtesy : Gulf today

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