Secondary Osteoporosis: When and How to Work Up - Brief Article

0 Comments | Family Practice News, Nov 15, 2000

Bone mineral density testing is particularly useful in identifying patients who need a battery of blood and urine tests to find a secondary cause for their bone loss, Dr. Kohlmeier said.

A bone mineral density (BMD) value that is more than one standard deviation less than age-, ethnicity-, and gender-matched controls warrants an evaluation for secondary causes of the bone loss. And a patient whose BMD measurement shows continued bone loss or a minimal increase in BMD after 2 years of therapy also needs further testing, she said.

Clinical indicators of the need for further evaluation include signs of Cushing's syndrome, Graves' disease, or other conditions that adversely affect bone mass. A recurrent fracture in spite of antiosteoporosis therapy is another red flag.

It's important to realize that all of the major clinical trials of osteoporosis therapy were restricted to patients who had no secondary cause of bone loss. In the real world, of course, primary care physicians see lots of patients with secondary causes. Until those secondary causes are recognized and, if possible, rectified, it's unrealistic to expect the same sort of success reported for antiosteoporosis drugs in clinical trials.

To evaluate patients for possible secondary causes of bone loss, Dr. Kohlmeier recommends a basic battery of tests: a serum calcium measurement looking for primary, secondary, or tertiary hyperparathyroidism; a 24-hour urine calcium test to home in on hypercalciuria, kidney stones, or hyperparathyroidism; a liver enzyme test; a TSH level test to identify overt or subclinical hyperthyroidism; and serum creatinine and blood urea nitrogen tests to detect renal insufficiency.

If any of these tests yield abnormal results, consider referral to an endocrinologist. Or, order a serum parathyroid hormone (PTH) measurement if either the serum calcium or 24-hour urine calcium test is elevated. An elevated serum PTH level points toward possible hyperparathyroidism, renal disease, or vitamin D deficiency.

If the serum PTH level is elevated or the 24-hour urine calcium level is low, measure the level of 25-hydroxyvitamin D. This can help nail down the diagnosis of vitamin D deficiency and may uncover an underlying malabsorption syndrome.

In a patient of cushingoid appearance, a 24-hour urine cortisol test or low-dose dexamethasone suppression test is useful.

Multiple myeloma is an uncommon cause of secondary osteoporosis, but one not to be missed. A CBC and serum or urine protein electrophoresis showing a homogeneous M spike can help establish the diagnosis.