QUANTITATIVE BONE DENSITOMETRY (continued):

Indications for Quantitative Bone Densitometry:

• Patients receiving long term gluco-corticoid therapy. Patients with primary asymptomatic hyperparathyroidism, or other patients at high risk for osteoporosis such as amenorrhea, anorexia nervosa, alcoholism, patients with atraumatic fractures, disuse atrophy, and similar conditions.
• Assessment of early postmenopausal bone loss as an indication to initiate estrogen replacement therapy.
• Diagnosis of osteoporosis suspected from radiographic findings or from clinical risk factors.
• Serial assessment of bone density, i.e., during treatment for osteoporosis or in anticipation of rapid bone loss.

A variety of metabolic disorders such as hyperparathyroidism, renal insufficiency, Cushing's syndrome, and amenorrhea in premenopausal women as well as chronic immobilization and chronic steroid or thyroid therapy are known to influence calcium metabolism and may affect the skeleton adversely. In these cases of secondary osteoporosis, bone density measurements are of particular importance because they may prompt therapeutic decisions such as reduction in medication or surgery.

Bone turnover increases significantly at menopause with a greater increase in bone resorption than bone formation resulting in accelerated loss of bone. One-third to one-half of bone loss in women may be attributable to the loss of ovarian function. Several studies have established the bone mass-preserving effect of estrogen therapy; if begun soon after menopause it reduces the subsequent rate of vertebral fractures by 50%. The benefits derived from estrogen therapy clearly seem to outweigh its adverse effects. However, it is unacceptable for many women and the level of bone mineral density at menopause and the magnitude of subsequent loss are important considerations in assessing the future risk of fracture and a decision to begin prophylaxis can be based on such considerations.

Serial measurement of bone density is accurate, providing guidance for clinical treatment. Measurements every 1-2 years are useful depending on the disease process. Studies have shown large annual loss of bone density from sites rich in trabecular bone in patients receiving high dose steroids. Similarly, large annual gains of bone have been observed in osteoporotic patients receiving treatment with a variety of therapeutic agents such as calcitonin, fluoride, biphosphonates, or parathyroid hormone. Considering the marked effect of some types of intervention, the magnitude of postmenopausal loss of bone, and the continued improvements in measurement precision, serial quantitative bone densitometry is valuable in determining therapeutic efficacy.

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