Chapter 38 Osteoporosis
INTRODUCTION
Description: Osteoporosis is characterized by loss of bone mass (calcium) that puts the patient at risk for fracture with minimal trauma or during activities of daily living. This process disproportionately affects older women and results in significant morbidity and mortality. Estimates of medical costs are as high as $10 billion each year in the United States.
Prevalence: Of women older than age 75 years (not receiving estrogen replacement), 40% have spine, hip, or forearm fractures; 80% of hip fractures occur in this group.
ETIOLOGY AND PATHOGENESIS
Causes: Alcohol use/abuse, chronic illness, diabetes mellitus, estrogen loss, especially early menopause, excessive caffeine use, family history of osteoporosis, high parity, high protein intake, inactivity/sedentary lifestyle, inadequate vitamin D intake or sun exposure, low body weight, medical therapy (anticonvulsants, corticosteroids, excess thyroid hormone replacement, long-term heparin or tetracycline use, loop diuretics, chemotherapy), poor diet/inadequate calcium intake (<1000 mg/day), white race or Asian, radiation therapy, smoking.
Risk Factors: Menopause (without estrogen replacement), inactivity, presence of other causes as listed previously. (Women suffer roughly a 10-fold increase in the normal rate of bone loss for a period of about 10 years beginning with the loss of ovarian function. This results in an average lifetime loss of approximately 35% of cortical bone mass and 50% of the more metabolically active trabecular bone. By comparison, men lose only about two thirds this amount.)
DIAGNOSTIC APPROACH
Workup and Evaluation
Imaging: Dual-energy x-ray absorptiometry (DEXA) or quantitative computed tomography. Routine radiographic studies (e.g., chest radiograph) do not detect changes until almost 30% of bone has been lost (approximately equal to fracture threshold, 1 g/cm2).
