Paget’s Disease - Metabolic Bone Disorders

PAGET’S DISEASE

Paget’s disease (osteitis deformans) is a disorder of localized rapid bone turnover, most commonly affecting the skull, femur, tibia, pelvic bones, and vertebrae. There is a primary proliferation of osteoclasts, which produces bone resorption. This is followed by a compensatory increase in osteoblastic activity that replaces the bone. As bone turnover continues, a classic mosaic (disorganized) pattern of bone develops. Because the diseased bone in Paget’s disease is highly vascularized and structurally weak, pathologic fractures occur. Structural bowing of the legs causes malalign-ment of the hip, knee, and ankle joints, which contributes to the development of arthritis and back and joint pain.

Paget’s disease occurs in about 2% to 3% of the population older than 50 years of age. The incidence is slightly greater in men than in women and increases with aging. A family history has been noted, with siblings developing the disease. The cause of Paget’s disease is not known.

Clinical Manifestations

Paget’s disease is insidious; most patients never know they have it. Some patients do not experience symptoms but have skeletal de-formity. A few patients have symptomatic deformity and pain. The condition is most frequently identified on x-ray during a routine physical examination or in the course of a workup for another problem. Sclerotic changes, skeletal deformities (eg, bowing of femur and tibia, enlargement of the skull, deformity of pelvic bones), and cortical thickening of the long bones occur.

In most patients, skeletal deformity involves the skull or long bones. The skull may thicken, and the patient may report that a hat no longer fits. In some cases of Paget’s disease, the cranium, but not the face, is enlarged. This gives the face a small, triangu-lar appearance. Most patients with skull involvement have im-paired hearing from cranial nerve compression and dysfunction. Other cranial nerves may also be compressed.

The femurs and tibiae tend to bow, producing a waddling gait. The spine is bent forward and is rigid; the chin rests on the chest. The thorax is compressed and immobile on respiration. The trunk is flexed on the legs to maintain balance; the arms are bent outward and forward and appear long in relation to the shortened trunk, giving the patient an apelike posture.

Pain, tenderness, and warmth over the bones may be noted. The pain is mild to moderate, deep, and aching; it increases with weight bearing if the lower extremities are involved. Pain and discomfort may precede skeletal deformities of Paget’s disease by years and are often wrongly attributed by the patient to old age or arthritis.

The temperature of the skin overlying the affected bone in-creases because of increased bone vascularity. Patients with large, highly vascular lesions may develop high-output cardiac failure because of the increased vascular bed and metabolic demands.

Assessment and Diagnostic Findings

Elevated serum alkaline phosphatase concentration and urinary hydroxyproline excretion reflect increased osteoblastic activity. Higher values suggest more active disease. Patients with Paget’s disease have normal blood calcium levels. X-rays confirm the di-agnosis of Paget’s disease. Local areas of demineralization and bone overgrowth produce characteristic mosaic patterns and ir-regularities. Bone scans demonstrate the extent of the disease. Bone biopsy may aid in the differential diagnosis.

Medical Management

Pain usually responds to administration of NSAIDs. Gait prob-lems from bowing of the legs are managed with walking aids, shoe lifts, and physical therapy. Weight is controlled to reduce stress on weakened bones and malaligned joints. Asymptomatic pa-tients may be managed with diets adequate in calcium and vita-min D and periodic monitoring.

Fractures, arthritis, and hearing loss are complications of Paget’s disease. Fractures are managed according to location. Healing occurs if fracture reduction, immobilization, and stability are ade-quate. Severe degenerative arthritis may require total joint re-placement. Loss of hearing is managed with hearing aids and communication techniques used with the hearing-impaired per-son (eg, lip reading, body language).

PHARMACOLOGIC THERAPY

Patients with moderate to severe disease may benefit from spe-cific antiosteoclastic therapy. Several medications reduce bone turnover, reverse the course of the disease, relieve pain, and im-prove mobility.

Calcitonin, a polypeptide hormone, retards bone resorption by decreasing the number and availability of osteoclasts. Calci-tonin therapy facilitates remodeling of abnormal bone into normal lamellar bone, relieves bone pain, and helps alleviate neurologic and biochemical signs and symptoms. Calcitonin is administered subcutaneously or by nasal inhalation. Side effects include flush-ing of the face and nausea. The effect of calcitonin therapy is evident in 3 to 6 months.

Bisphosphonates, such as etidronate disodium (Didronel) and alendronate sodium (Fosamax), produce rapid reduction in bone turnover and relief of pain. They also reduce serum alkaline phosphatase and urinary hydroxyproline levels. Food inhibits ab-sorption of these medications. Adequate daily calcium (1500 mg) and vitamin D (400 to 600 IU) are required during therapy.

Plicamycin (Mithracin), a cytotoxic antibiotic, may be used to control the disease. This medication is reserved for severely af-fected patients with neurologic compromise and for those whose disease is resistant to other therapy. This medication has dramatic effects on pain reduction and on serum calcium, alkaline phos-phatase, and urinary hydroxyproline levels. It is administered by IV infusion and requires that hepatic, renal, and bone marrow function be monitored during therapy. Clinical remissions may continue for months after the medication is discontinued.

Gerontologic Considerations

Careful assessment of the patient’s pain and discomfort is neces-sary. Patient teaching helps the patient understand the treatment regimen, the need for a diet with adequate calcium and vitamin D, and how to compensate for altered musculoskeletal function-ing. The home environment is assessed for safety to prevent falls and to reduce the risk for fracture. Strategies for coping with a chronic health problem and its effect on quality of life need to be developed.