A 65-year-old white woman presents for an annual examination. She feels well except for occasional nocturnal leg cramp and mild abdominal bloating. She takes a multivitamin and a supplement containing 600 mg calcium carbonate and 200 international units of vitamin D twice daily. She takes no prescription medications. Physical examination is unremarkable for her age. In completing the appropriate screening tests, you order a dual x-ray absorptiometry (DXA) to evaluate whether the patient has osteoporosis. DXA results reveal a T-score of −3.0 at the total hip and −2.7 at the femoral neck (osteoporosis: less than −2.5). Since her Z-score is −2.0, you proceed with an evaluation of secondary osteoporosis. Laboratory evaluation reveals
What is the likely cause of her osteoporosis?A) Hypoparathyroidism
Screening for osteoporosis in women is recommended at age 65 for most women and at age 60 for those with risk factors, including hyperparathyroidism, corticosteroid use greater than 3 months, cigarette smoking, low body weight, or documented fragility fracture. Although most women with osteoporosis will have primary osteoporosis, her hypocalcemia and low vitamin D levels suggest that this woman’s osteoporosis is due to a secondary cause. The GI symptoms and the iron deficiency anemia suggest that her hypovitaminosis D is due to intestinal malabsorption. Celiac sprue is relatively common (as high as 1% of the Caucasian population) and often presents with mild symptoms. A tissue transglutaminase or antiendomysial antibody test will provide important diagnostic information. Hypoparathyroidism causes hypocalcemia but is not associated with vitamin D deficiency or osteoporosis. Estrogen deficiency is an important contributing factor to the skeletal loss of calcium that occurs in women at the time of menopause, but is associated with normal calcium and vitamin D levels and would not account for the iron deficiency. Hypercalciuria of any cause will lead to kidney stones but does not cause hypocalcemia or hypovitaminosis D. Although primary biliary cirrhosis may present with mild symptoms (usually pruritus) and vitamin D deficiency, the alkaline phosphatase is always elevated (often three to five times upper normal) in this disease. Again, recent studies show that sprue (gluten-sensitive enteropathy) is much commoner than PBC.