To determine if differing degrees of levothyroxine (LT4) suppression therapy for benign and malignant thyroid disease are associated with proportionately increased rates of bone loss, this longitudinal assessment of bone densitometry changes (single-photon and dual-photon absorptiometry) was conducted in three groups of subjects: 24 thyroid cancer patients who were treated with near-total thyroidectomy, radioiodine ablation, and aggressive LT4-suppression; 44 patients who were treated with more conservative LT4-suppression for benign thyroid disorders; and 24 normal controls. Bone densitometry values were adjusted for age, weight, height, and menopausal status. The rates of bone loss in benign LT4-suppressed patients were greater than those in controls at the midradius, distal radius, lumbar spine, and femoral neck. The rates of loss in the thyroid cancer patients were also greater than those in the controls at all four sites and greater than in the benign LT4-suppressed patients at the midradius, distal radius, and femoral neck but not in the lumbar spine. Rates of bone loss were not significantly correlated with LT4 dose or with the serum level of T4 or TSH. LT4-suppression therapy for benign thyroid disease is associated with accelerated bone loss. More aggressive LT4-suppression for thyroid cancer is associated with even greater bone loss, particularly in cortical bone regions. These risks must be weighed against the benefits of LT4 therapy in individual patients.

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Primary hyperparathyroidism (HPT) presents most commonly as a mild elevation of the serum calcium concentration in an asymptomatic individual. There are conflicting data regarding the effects of mild primary HPT on bone mass. This cross-sectional study was conducted to examine this question further and to determine whether estrogen replacement therapy (ERT) in postmenopausal women with primary HPT might be beneficial. We measured bone mass in 59 women with mild asymptomatic primary HPT, of whom 43 (HPT) had never taken and 16 (estrogen-replaced HPT) were currently taking ERT. We also studied 84 healthy normocalcemic women who were not on ERT (controls) and 45 who were on ERT (estrogen-replaced controls). After adjustment for age, height, and weight, mean bone mass values in the HPT group were significantly reduced in the midradius (20%), distal radius (20%), lumbar spine (17%), and femoral neck (11%) compared with the controls. The estrogen-replaced HPT group had mean bone mass values greater than those in the HPT group, similar to those in the controls, and lower than those in the estrogen-replaced controls. Mild asymptomatic primary HPT results in bone loss from both the appendicular and axial skeleton, and ERT in postmenopausal women with primary HPT may ameliorate this loss.

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