Conference Coverage

How to rule out secondary causes of osteoporosis


 

EXPERT ANALYSIS FROM THE ANNUAL INTERNAL MEDICINE PROGRAM

– Everyone diagnosed with osteoporosis deserves a laboratory assessment to rule out unsuspected secondary causes, according to Sterling West, MD. And he’s got a doozy of a workup he recommends to primary care physicians as “incredibly cost effective.”

“With this workup you’ll identify 98% of abnormalities at a mean cost of $366 per diagnosis. That’s incredibly cost effective. You’re going to get a lot of information with actually not very much outlay at all,” he said at a conference on internal medicine sponsored by the University of Colorado.

Dr. Sterling West professor of medicine, University of Colorado Bruce Jancin/Frontline Medical News

Dr. Sterling West

Applying this laboratory screening regimen to all patients diagnosed with osteoporosis is warranted because unsuspected secondary causes of the skeletal disease are so common. In various studies, laboratory screening has revealed a secondary cause in up to one third of postmenopausal women with osteoporosis, in up to half of men, and in 50%-80% of premenopausal osteoporosis patients, noted Dr. West, professor of medicine at the university.

The tests he advocates that primary care physicians order in all their patients with osteoporosis include a complete blood count, a complete metabolic panel, a 24-hour urine calcium/sodium/creatinine, a serum 25-hydroxyvitamin D level, and a serum phosphorus. In addition, men with osteoporosis should have their serum testosterone measured. A thyroid-stimulating hormone level should be obtained in patients who are taking thyroxine or if they look clinically hyperthyroid.

A measurement of parathyroid hormone is warranted as part of the screen in patients with an abnormal serum calcium. If the parathyroid hormone is normal, hyperparathyroidism can be ruled out.

Ordering a serum protein electrophoresis to check for multiple myeloma is appropriate in osteoporotic patients over age 50 years with an abnormal complete blood count.

This basic laboratory workup will identify patients with the relatively common secondary causes of low bone mineral density which account for 98% of all cases. These causes include vitamin D deficiency, malabsorption, hypogonadism, hypercalciuria, and myeloma.

“Leave the other 2% to me,” the rheumatologist suggested.

Special laboratory tests Dr. Sterling recommended that are best left to bone disease specialists include bone turnover markers, a serum tryptase/urine N-methylhistamine to screen for systemic mastocytosis, antitransglutaminase antibodies for celiac disease, a 24-hour urinary free cortisol and/or overnight dexamethasone suppression test to identify patients with Cushing syndrome, and bone biopsy.

Who should be referred to a bone specialist for a more extensive workup?

“If somebody is losing bone or fracturing and they’re on appropriate therapy and you believe they’re taking their medication, that’s for sure somebody that we should see. Also, a premenopausal woman with a high Z score who has had a fracture that’s atypical. And patients with stage 4 or 5 chronic kidney disease; those are some of the toughest cases and are best referred to a bone expert,” Dr. Sterling said.

On the other hand, if an osteoporotic patient simply can’t tolerate guideline-recommended initial therapy with an oral bisphosphonate such as alendronate (Fosamax) or risedronate (Actonel), there’s no need to bring in a specialist. Simply switch the patient to denosumab (Prolia), a monoclonal antibody against receptor activator of nuclear factor kappa-B ligand, administered by subcutaneous injection once every 6 months. The cost is about $2,200 per year, but the drug is covered by Medicare Part B. Clinical trials have demonstrated that denosumab boosts bone mineral density by 6%-9%, with an absolute 5% reduction in fractures and a 40%-68% relative risk reduction, he noted.

Dr. West reported having no financial conflicts of interest regarding his presentation.

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