Introduction to Osteoporosis

Introduction

In osteoporosis, a metabolic bone disorder, the rate of bone resorption accelerates while the rate of bone formation slows down, causing a loss of bone mass. Bones affected by this disease lose calcium and phosphate salts and thus become porous, brittle, and abnormally vulnerable to fracture.

Osteoporosis may be primary or secondary to an underlying disease. Primary osteoporosis is commonly called senile or postmenopausal osteoporosis because it’s most common in elderly, postmenopausal women.

Causes
The cause of primary osteoporosis is unknown; however, a mild but prolonged negative calcium balance, resulting from an inadequate dietary intake of calcium, may be an important contributing factor—as may declining gonadal adrenal function, faulty protein metabolism due to estrogen deficiency, and a sedentary lifestyle.

Causes of secondary osteoporosis include 

• prolonged therapy with steroids or heparin, 
• total immobilization or disuse of a bone (as with hemiplegia, for example), 
• alcoholism, 
• malnutrition,
•  malabsorption,
•  scurvy, 
• lactose intolerance, 
• hyperthyroidism, 
• osteogenesis imperfecta, and 
• Sudeck’s atrophy (localized to hands and feet, with recurring attacks).

Signs and symptoms
Osteoporosis is usually discovered when an elderly person bends to lift something, hears a snapping sound, and then feels a sudden pain in the lower back. Vertebral collapse, producing a backache with pain that radiates around the trunk, is the most common presenting feature. Any movement or jarring aggravates the backache.
In another common pattern, osteoporosis can develop insidiously, with increasing deformity, kyphosis, loss of height, and a markedly aged appearance. As vertebral bodies weaken, spontaneous wedge fractures, pathologic fractures of the neck and femur, Colles’ fractures after a minor fall, and hip fractures are all common.
Osteoporosis primarily affects the weight-bearing vertebrae. Only when the condition is advanced or severe, as in Cushing’s syndrome or hyperthyroidism, do comparable changes occur in the skull, ribs, and long bones.

Diagnosis
Differential diagnosis must exclude other causes of rarefying bone disease, especially those affecting the spine, such as metastatic carcinoma and advanced multiple myeloma. Initial evaluation attempts to identify the specific cause of osteoporosis through the patient history. Diagnostic tests include the following:

• X-rays show typical degeneration in the lower thoracic and lumbar vertebrae. The vertebral bodies may appear flattened and may look denser than normal.
• Bone mineral density (BMD) shows demineralization. Loss of bone mineral becomes evident in later stages.
• Dual- or single-photon absorptiometry allows measurement of bone mass, which helps to assess the extremities, hips, and spine.
• Serum calcium, phosphorus, and alkaline phosphatase levels are all within normal limits, but parathyroid hormone level may be elevated.
• Bone biopsy shows thin, porous, but otherwise normal-looking bone.

Treatment
Effective treatment aims to prevent additional fractures and control pain. A physical therapy program, emphasizing gentle exercise and activity, is an important part of the treatment. In women, estrogen, to be started within 3 years after menopause, may be given to decrease the rate of bone resorption; sodium fluoride, to stimulate bone formation; and calcium and vitamin D, to support normal bone metabolism. However, drug therapy merely arrests osteoporosis and doesn’t cure it.
Similar therapies are used in men. Testosterone replacement may be used to increase BMD in men with low levels. (It’s contraindicated in men with prostate cancer.) A digital rectal examination and prostate-specific antigen test are performed before therapy and yearly thereafter.