Osteoporosis in a premenopausal woman is a rare diagnosis. Nevertheless, I am constantly surprised by the number of younger women labeled with this diagnosis. The rate is higher than expected because the diagnosis is being applied incorrectly. A low bone density alone does not establish a diagnosis of osteoporosis. In premenopausal women, the association of bone mass and fracture risk is not the same as for postmenopausal women. The number of fractures that occur in premenopausal women is very low compared with the frequency of fractures in older postmenopausal women. At any given level of bone density, the risk of fracture increases with age because of progressive loss of bone microstructure.
LOW BONE DENSITY ON DXA SCAN
Screening bone density scans are not recommended for premenopausal women. When bone density machines were new and first installed in many doctors' offices or clinics, staff members acted as volunteers to test the machines. Commonly, the staff members were young women who happened to have low bone density. If the criteria for postmenopausal women were applied using their T-score results, their diagnosis would be “osteopenia” or osteoporosis. Understandably, these staff members went into panic mode when they were given one of these diagnoses. However, T-scores are not used in premenopausal women, men under the age of fifty, or children, according to guidelines established by the International Society of Clinical Densitometry.
Z-scores that compare the bone density results to individuals of the same age, ethnicity, and sex are used instead. For example, if you were a thirty-twoyear-old Asian woman, your results would be compared with other thirty-twoyear-old Asian women in the database. If the Z-scores were higher than -2.0, the results would be considered “within the expected range for age.” If the lowest Z-score were -2.0 or lower, the results would be considered “below the expected range for age.” Approximately 2.5 percent of premenopausal women will fall into this category.
Since bone density measured by DXA scan is two-dimensional, it does not take into account bone size. A petite woman with small bones will have a result lower than a woman with larger bones, although they may have the same actual bone mineral content. This is a limitation of the measurement device.
One low bone density measurement does not mean you are actually losing bone. Serial measurements are needed to determine loss. Bone density for the US female population is distributed from low to high in a bell-shaped curve. This means that not everyone can be average or above normal. A low bone density may mean that you are on the low end of the bell-shaped curve.
Measurement of bone density is recommended only in situations such as disease or medicine exposure that may cause bone loss or low-trauma fracture of the hip or spine.
UNDERLYING CAUSES
A thorough history and physical examination may provide the majority of clues that explain low bone density. Additional investigation with appropriate laboratory evaluation is also indicated in searching for an explanation for major fracture or low bone density below the expected range for age.
Research has shown that the most common cause of fracture or unexpectedly low bone density in younger women is steroid use. Other underlying causes were found in at least half of women, including other medicines (cancer chemotherapy or older seizure medicines), low estrogen status, and malabsorption. Low estrogen status can be the result of medicines (such as low-dose birth control pills, Depo-Provera®, and treatment of endometriosis) or the lack of menstrual periods. Diseases affecting the intestine (celiac disease or inflammatory bowel disease) may prevent adequate nutrition and absorption of vital nutrients, including vitamin D and calcium.
Recent research has raised concern about other medicines, including anti-depressants, called SSRIs, and acid reflux medicines, called proton pump inhibitors (PPIs). The bone connection with common problems and medicines are explored in more detail in subsequent sections.
The majority of premenopausal women with low bone density and no fractures have stable bone density and no underlying causes. This means that repeat DXA scans do not show significant bone loss. Most likely, these women have low peak bone mass and their short-term risk of fracture is low.
MANAGEMENT
The usual general measures of good nutrition to maintain a healthy weight, exercise, and adequate calcium and vitamin D are indicated for everyone. Decreasing risk factors, such as avoiding smoking and limiting alcoholic beverages, will also help.
If an underlying cause is found, lessening the effect of the medicine or disease is the goal. Osteoporosis prescription medicines are approved for use only in premenopausal women who are taking steroids. Although data is limited, treatment studies show that premenopausal women taking steroids, such as prednisone, do not appear to be at high risk for fracture. The bisphosphonates, Fosamax and Actonel, are FDA-approved for premenopausal women taking steroids. These medicines should not be given to women who are actively trying to become pregnant or are breastfeeding.
Sometimes the cause of low bone density is decreased bone formation. Therefore, bisphosphonates would not be expected to improve bone density. Treatment with Forteo, which increases bone formation, is being evaluated in research studies. Therapy with Forteo may be an option in the future for select premenopausal women.
The perimenopause-to-menopause transition period is an appropriate time to readdress bone density and fracture risk. With the loss of estrogen, bone loss accelerates unless measures are taken to prevent bone loss.
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The Bare Bones
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