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RISK FACTORS
Pathophysiologic factors
Current understanding of osteoporosis suggests that four distinct pathophysiologic
factors contribute to development of the disease.5
In any given patient, each factor may contribute independently to osteoporosis;
however, it is easiest to consider each factor separately.
Low peak bone mass is one determinant of osteoporosis risk in that the higher the mass, the more bone that must be lost before the osteoporosis threshold is reached.5 Genetic factors probably contribute to most of the variance in peak bone mass between individuals, but other factors, including level of activity and nutrition, are also probably important in that they allow the skeleton to achieve its genetically pre-determined maximum.7
The bone loss that occurs due to age and menopause have been discussed previously.
The NOF in collaboration with a multidisciplinary coalition of clinical experts, recommends that all postmenopausal women be evaluated for risk of fracture. During evaluation, the organization recommends that particular attention be paid to modifiable and nonmodifiable risk factors and to known secondary causes of osteoporosis.11
Nonmodifiable:
Potentially modifiable:
Note that poor health and fraility, which may or may not be modifiable, appear under both headings. The four items in bold face-personal history of fracture as an adult, history of fracture in first-degree relative, smoking, and low body weight- were demonstrated in a large, ongoing prospective US study to be key factors in determining the risk of hip fracture (independent of bone fracture). |
If more than one risk factor is present, BMD testing may be indicated to further direct appropriate therapy. If a secondary cause of osteoporosis is suspected, both biochemical tests and BMD measurements may help determine the course of management.
Secondary causes of osteoporosis represent additional risk factors in those patients at risk of developing involutional, or age-related, osteoporosis.5,11 Several diseases or conditions, and drugs associated with secondary osteoporosis are enumerated.
Diseases and drugs associated with an increased risk of generalized osteoporosis in adults11
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DISEASES
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DRUGS
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Conditions resulting in a relative excess of circulating corticosteroids, such as Cushing's syndrome or exogenously administered steroids, cause accelerated bone loss. This is due to an increased rate of bone resorption and a decreased rate of bone formation.12 Reductions are more pronounced in trabecular bone, from 10-40% in patients receiving a high cumulative dose. Bone loss is reversible upon withdrawl of glucocorticoid treatment. Comprehensive guidelines for the prevention and treatment of osteoporosis in patients on corticosteroid therapy have been released.13 It appears from these guidelines that oral steroid doses of > 7.5 mg per day of prednisone for 6 months or more contribute to rapid bone loss. The long term effects of inhaled corticosteroid therapy on bone density and fracture risk is currently unknown.14
Hyperthyroidism (whether endogenous or due to exogenously administered thyroid hormone) leads to increased bone turnover.5,15 Hyperthyroidism is associated with loss of both trabecular and cortical bone.15 Chronic use of enzyme-inducing anticonvulsant drugs (phenytoin or phenobarbital) leads to diminished bone mineral density secondary to enhancement of vitamin D degradation.5 Methotrexate use has also been associated with an increase in fracture risk.5 GnRH analogs used to treat endometriosis; excessive use of aluminum-containing antacids, thyroxine; heparin and certain drugs used in cancer treatment also causes osteoporosis.
Individuals who have undergone gastrectomy have a well-documented increase in fracture risk, presumably due to decreased dietary absorption of vitamin D or other metabolic changes. Prolonged bed rest and sedentary lifestyle are also important risk factors for osteoporosis.11
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