Bone mineral density in premenopausal women receiving long-term physiological doses of levothyroxine
A. W. Kung and K. K. Pun
Department of Medicine, University of Hong Kong, Queen Mary Hospital.
Total body and regional bone mineral density (BMD) levels were determined
in 26 premenopausal women with Hashimoto's thyroiditis receiving long-term
physiological doses of levothyroxine sodium replacement therapy. The BMD
levels of each patient were compared with the mean of the BMD levels of
age-matched normal controls. The mean levothyroxine sodium dose was 111 +/-
6 micrograms/d, and the mean duration of treatment was 7.5 +/- 5.3 years
(range, 1 to 24 years). Dietary calcium intake was similar in both groups,
as were serum thyroxine, triiodothyronine, free thyroxine index, and
thyrotropin levels. Women receiving the levothyroxine treatment had normal
total body BMD levels but had significantly lower BMD levels at the femoral
neck (-5.7%), femoral trochanter (-7.0%), Ward's triangle (-10.6%), both
arms (right, -7.8%; left, -8.9%), and pelvis (-4.9%). In contrast, lumbar
spine BMD levels were similar in the two groups. There was no correlation
between the total body or different regional BMD levels and the duration or
dosage of levothyroxine treatment or thyroid function test results.
However, the z score of the femoral neck of these patients showed a
significant negative correlation with their serum free thyroxine index
levels. We conclude that patients receiving physiological doses of
levothyroxine may have decreased bone density. Thyroid functions in
patients receiving long-term levothyroxine treatment should be closely
monitored and bone densitometry should be performed in patients at risk for
osteoporosis.
