FORT LAUDERDALE, FLA. — Biochemical screening of patients with Paget's disease of bone should always include measurement of parathyroid hormone levels, Dr. Maria Luisa Brandi advised at a meeting sponsored by the Paget's Foundation for Paget's Disease of Bone and Related Disorders.
The coexistence of Paget's disease of bone and hyperparathyroidism, first described in 1948, is still not well understood. In studies, approximately 12%–18% of Paget's disease patients have elevated levels of parathyroid hormone (PTH), most of which represent secondary hyperparathyroidism. Yet measurement of PTH is still not routine, and “hyperparathyroidism in Paget's disease of bone is often overlooked,” said Dr. Brandi, professor of endocrinology and metabolism at the University of Florence, Italy.
Both Paget's disease and hyperparathyroidism are capable of causing bone pain, and bone biomarkers are elevated in both disorders. Increased marrow fibrosis and vascularity are common histologic features of both. But the two disorders differ in several histologic features. Hypercalcemia and hypercalciuria, only occasional findings in Paget's disease, are commonly seen in hyperparathyroidism. Malignant bone tumors are present in up to 1% of Paget's disease patients but are rare in hyperparathyroidism, she said at the conference, also sponsored by the National Institutes of Health and Columbia University, New York.
Increasing lines of evidence suggest that the cooccurrence of primary hyperparathyroidism with Paget's disease is due to the chance association of two diseases that are common in the elderly. Autopsy studies in Paget's disease patients failed to uncover consistent parathyroid gland abnormalities.
Furthermore, the prevalence and gender distribution of primary hyperparathyroidism in Paget's disease resembles that of the elderly population as a whole.
Most genetic studies have failed to find overlapping genes in the two disorders, but recent data suggest there might be some interactions among gene products, she noted.
Regardless of etiology, an excess of PTH is likely to have an exaggerated impact at skeletal sites affected by Paget's disease. Therefore, biochemical screening of patients with Paget's disease should include evaluation of serum calcium, phosphate, and PTH.
Parathyroidectomy is indicated in patients found to have both disorders. Conversely, patients who have primary hyperparathyroidism and high bone turnover after parathyroidectomy should undergo diagnostic screening for Paget's disease, Dr. Brandi recommended.
Secondary hyperparathyroidism can also result directly from the increased bone turnover in Paget's disease—a consequence of increased calcium demands during periods of pagetic bone formation—or from bisphosphonate treatment. Dietary supplementation with calcium and vitamin D can protect against this problem in patients undergoing bisphosphonate treatment, she said.