Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 55-year-old woman is evaluated for a new-patient visit. Medical history is significant for an eating disorder. Although she has maintained a normal weight for the past 20 years, she notes that prior to that time her weight would fluctuate in a range correlating with BMIs of 17 to 19. She has otherwise been healthy and currently feels well. She is postmenopausal and a never-smoker. Family history is significant for postmenopausal osteoporosis in her mother. Her medications are over-the-counter calcium and vitamin D supplements.

On physical examination, temperature is 36.3 °C (97.3 °F), blood pressure is 137/81 mm Hg, pulse rate is 76/min, and respiration rate is 11/min. BMI is 21. She has mild thoracic kyphosis but no skeletal tenderness. The remainder of the examination is unremarkable.

Results of laboratory studies are significant for a serum calcium level of 9.1 mg/dL (2.3 mmol/L) and 25-hydroxyvitamin D level of 40 ng/mL (99.8 nmol/L); thyroid function studies are normal.

Dual-energy x-ray absorptiometry (DEXA) scan shows T-scores of –1.8 in the femoral neck and –1.9 in the lumbar spine. Ten-year fracture risk using the Fracture Risk Assessment Tool (FRAX) is 6.9% for major osteoporotic fracture and 0.7% for hip fracture. Plain radiographs of the spine show no evidence of compression fracture.

Which of the following is the most appropriate management of this patient?

A. Begin raloxifene
B. Repeat DEXA scan in 2 years
C. Replace calcium with cholecalciferol
D. Start bisphosphonate therapy

MKSAP Answer and Critique

The correct answer is B. Repeat DEXA scan in 2 years.

A repeat dual-energy x-ray absorptiometry (DEXA) scan should be repeated in 2 years in this patient with low bone mass and relatively low 10-year fracture risk. The Fracture Risk Assessment Tool (FRAX) calculator defines the 10-year fracture risk for patients with T-scores in the −1.0 to −2.5 ranges. The FRAX calculator incorporates multiple risk factors including sex, fracture history, femoral neck bone mineral density, glucocorticoid use, smoking, BMI, age, and alcohol intake to determine projected fracture risk. If the risk of major osteoporotic fracture is greater than or equal to 20% or the risk of hip fracture is greater than or equal to 3%, then the patient’s benefit from therapy exceeds the risk, and she should be offered treatment. Because of her history of low body weight and limited nutritional intake during the time of development of peak bone mass, she is at increased risk for low bone mass or osteoporosis and is therefore an appropriate candidate for early screening. Her DEXA scan shows low bone mass. Spine film shows no evidence of fracture. Additionally, her calcium and vitamin D levels are normal. Continuing lifestyle activities (such as maximizing weight-bearing exercise and avoidance of tobacco or excessive alcohol) in addition to calcium and vitamin D supplementation is appropriate management of this patient.

Raloxifene is a selective estrogen receptor modulator (SERM) that is a treatment option for women with osteoporosis because it has been shown to increase bone mineral density and reduce the risk of vertebral (but not nonvertebral) fractures. However, raloxifene is also associated with an increased risk of thromboembolic events and vasomotor symptoms. There is limited data supporting use of raloxifene or other SERMs for treating patients with low bone mass, although some guidelines recommend considering treatment in patients with low bone mass and 10-year fracture risk determined by the FRAX calculator of greater than or equal to 20% for a major osteoporotic fracture or greater than or equal to 3% for hip fracture. Raloxifene would therefore not be appropriate therapy for this patient.

Cholecalciferol (D₃), a metabolite of vitamin D, is commonly used to supplement low serum vitamin D levels in patients with vitamin D deficiency. This patient has normal serum vitamin D levels; therefore, there is no indication for treatment with vitamin D metabolites.

Bisphosphonates are considered first-line therapy for osteoporosis, although they are not used routinely in women with low bone mass. Similar to the use of SERM therapy, guidelines recommend consideration of treatment with a bisphosphonate for low bone mass only if there is 10-year fracture risk determined by the FRAX calculator of greater than or equal to 20% for a major osteoporotic fracture or greater than or equal to 3% for hip fracture.

Key Point

• Treatment for low bone mass in postmenopausal women involves lifestyle modification (maximizing weight-bearing exercise and avoidance of tobacco or excessive alcohol) and vitamin D and calcium supplementation; the need for pharmacologic therapy is based on the 10-year estimated fracture risk (≥20% for a major osteoporotic fracture or ≥3% for hip fracture).

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