Paget’s Disease
Also known as osteitis deformans, Paget’s disease is a slowly progressive metabolic bone disease characterized by an initial phase of excessive bone resorption (osteoclastic phase), followed by a reactive phase of excessive abnormal bone formation (osteoblastic phase). The new bone structure, which is chaotic, fragile, and weak, causes painful deformities of the external contour and the internal structures.
Paget’s disease usually affects one or several skeletal areas (most commonly the spine, pelvis, femur, and skull). Occasionally, the patient will have widely distributed skeletal deformity. In about 5% of patients, the involved bone will undergo malignant changes.
The disease can be fatal, particularly when associated with heart failure (widespread disease creates a continuous need for high cardiac output), bone sarcoma, or giant cell tumors.
Causes
Although the disease’s exact cause isn’t known, one theory suggests that a slow or dormant viral infection (possibly mumps) causes a dormant skeletal infection, which surfaces many years later as Paget’s disease.
Complications
Involved sites may fracture easily after only minor trauma. These fractures heal slowly and usually incompletely. Vertebral collapse or vascular changes that affect the spinal cord could lead to paraplegia. Bony impingement on the cranial nerves may cause blindness and hearing loss with tinnitus and vertigo.
Other complications include osteoarthritis, sarcoma, hypertension, renal calculi, hypercalcemia, gout, heart failure, and a waddling gait (from softened pelvic bones).
Assessment
Clinical effects vary. The patient with early disease may be asymptomatic. As the disease progresses, he may report severe,
persistent pain. If abnormal bone impinges on the spinal cord or sensory nerve root, he may complain of impaired mobility and increased pain with weight bearing.
persistent pain. If abnormal bone impinges on the spinal cord or sensory nerve root, he may complain of impaired mobility and increased pain with weight bearing.
If the patient’s head is involved, inspection may reveal characteristic cranial enlargement over the frontal and occipital areas. The patient may comment that his hat size has increased, and he may have headaches. Other deformities include kyphosis (spinal curvature caused by compression fractures of affected vertebrae) accompanied by a barrel-shaped chest and asymmetrical bowing of the tibia and femur, which typically reduces height. Palpation may detect warmth and tenderness over affected sites.
Diagnostic tests
X-ray studies performed before overt symptoms develop show bone expansion and increased bone density.
Bone scans (more sensitive than X-rays) clearly show early pagetic lesions (the radioisotope concentrates in areas of active disease).
Bone biopsy may show bone tissue that has a characteristic mosaic pattern.
Red blood cell count indicates anemia.
Serum alkaline phosphatase level—an index of osteoblastic activity and bone formation—is elevated.
A 24-hour urinalysis demonstrates elevated hydroxyproline levels. Hydroxyproline, an amino acid excreted by the kidneys, provides an index of osteoblastic hyperactivity.
Urinary collagen pyridinoline indicates rate of bone resorption and is more sensitive than the test for urinary hydroxyproline.
