Paget's disease and back pain.

Paget's disease of bone is a rare cause of back pain, often diagnosed on non-contrast radiography performed for other purposes or when the patient discovers swelling of the long bones. Early in the disease, bone is resorbed and the affected areas become vascularized. Resorption is followed by formation of new Paget's bone, which is deposited compactly and non-structurally. The process of bone resorption and formation is very active, with the rate of bone turnover increasing 20-fold over the normal rate. This process results in a characteristic pattern on non-contrast radiography that includes areas of bone resorption called localized osteoporosis. The areas of new bone formation are irregularly expanded cortex and compact substance, a striated pattern with areas of varying density, reflecting the chaotic nature of new bone formation.

The prevalence of Paget's disease is approximately 2% and is rare in India, Japan, the Middle East, and Scandinavia. Although patients with Paget's disease are most often asymptomatic and their disease is an incidental finding on radiographs performed for other reasons, they often present with back pain. The etiology of back pain in Paget's disease is thought to be multifactorial. The pain may be caused by the resorption process itself or by deformation of the facet joints by new bone formation. Both of these processes alter the functional stability of the spine and worsen existing facet arthropathy.

Patients with Paget's disease may also have thickening and widening of the long bones and enlargement of the skull due to new bone formation. Rarely, excess bone growth at the base of the skull may cause compression of the brainstem, with catastrophic consequences. Secondary hearing loss may occur due to compression of the eighth cranial nerve by newly formed bone or direct involvement of small bones in the pathological process. Occasionally, excess bone formation in the spine may cause compression of the spinal cord, which, if untreated, may lead to paraplegia. Pathologic fractures due to excessive vertebral resorption may cause acute back pain. Secondary hip pain due to calcific periarthritis may also occur. Kidney stones and gout are common, especially in men with Paget's disease. In less than 1%, the bone lesion may develop into a malignant osteosarcoma.

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Symptoms of Paget's disease

Although the disease is asymptomatic, pain is a common complaint that ultimately leads the physician to diagnose Paget's disease. Seemingly minor trauma may result in pathologic vertebral compression fractures. Pain with motion in the affected bones is often detected on physical examination, as is excessive bone growth by palpation of the skull or other affected bones. Neurologic signs may be present due to secondary nerve compression from both the bone growth and pathologic fractures. Pain with motion in peripheral joints, especially the hip due to calcific periarthritis, is a common finding in patients with Paget's disease. Hearing loss is also noted.

Survey

As noted above, Paget's disease is often diagnosed incidentally when a patient undergoes radiographic examination for an entirely unrelated reason, such as intravenous pyelography for kidney stones. The classic radiographic appearance of areas of bone resorption with surrounding dense areas and chaotic bone structure suggest the diagnosis of Paget's disease. Radionuclide bone scanning can be used in patients with Paget's disease to determine the extent of the lesion, since not all bone lesions are clinically evident. MRI is indicated in all patients with suspected Paget's disease who have evidence of spinal cord compression. Serum creatinine and blood chemistry including serum calcium are indicated in all patients with Paget's disease. Alkaline phosphatase levels are elevated, especially during the resorptive phase. Given the increased incidence of hearing loss in patients with Paget's disease, audiometric testing is indicated.

Differential diagnosis

Many other bone diseases, including osteoporosis, myeloma, osteopetrosis, and primary and metastatic bone tumors, can mimic the clinical features of Paget's disease. Acromegaly is also a common clinical feature. Metastatic tumors from the prostate or breast can cause pathological fractures of the spine and ribs and metastases to the bones of the skull, which may be mistaken for Paget's disease.

Treatment of Paget's disease

Many patients with asymptomatic Paget's disease require only psychological support. Treatment of pain associated with Paget's disease should begin with acetaminophen, NSAIDs. Narcotic analgesics may need to be added for severe pain associated with pathological fractures. Orthopedic devices such as the Kesh brace and rib bandage help stabilize the spine and ribs and should be used for pathological fractures. Local heat and cold applications may also be helpful. Repetitive movements that trigger the syndrome should be avoided. In patients who do not respond to these treatments, injections of local anesthetics and steroids into the affected areas in the form of intercostal and epidural blocks are indicated. In special cases, spinal administration of narcotic analgesics may be effective.

In patients who do not respond to these treatments, calcitonin and zoledronate have been used with some success. Rarely, if bone destruction is excessive, cytostatic agents such as dactinomycin may be required. High-dose pulse steroid therapy has also been shown to be symptomatic.

Side effects and complications

The primary complications of Paget's disease are related to the bone resorption and formation phases. Excessive bone resorption may result in vertebral compression fractures, rib fractures, and occasional long bone fractures. Excessive bone formation results in compression of neural structures, which may cause hearing loss, myelopathy, and paraplegia. Renal stones and gout are seen with increased frequency, especially in men with Paget's disease. Rarely, new bone formation is so extensive that it causes secondary hypersystolic heart failure due to increased blood flow. As discussed above, malignancy of the affected bone occurs in approximately 1% of patients with Paget's disease.

Careful evaluation of patients with Paget's disease is necessary to prevent possible complications of the disease. The clinician should be alert for subtle signs of compression of the brainstem and spinal cord. Epidural and intercostal injections of local anesthetics and steroids may provide good temporary relief of pain associated with Paget's disease that has not been controlled by pharmacotherapy.