ACCELERATED BONE DEGRADATION IN THYROID-CARCINOMA PATIENTS DURING THYROXINE TREATMENT, MEASURED BY DETERMINATION OF THE CARBOXYTERMINAL TELOPEPTIDE REGION OF TYPE-I COLLAGEN IN SERUM

We studied the effects of long-term suppressive thyroxine treatment on serum markers of bone collagen synthesis and degradation in thyroid c arcinoma patients, and the relationship of these effects to the serum concentrations of thyrotropin, free thyroxine and free triiodothyronin e were investigated. Thirty-seven thyroid carcinoma patients receiving a stable thyroxine dose, and thirty-five controls participated in a c ross-sectional study. Bone collagen synthesis and degradation were mea sured by using specific radioimmunoassays to determine the serum conce ntrations of carboxyterminal propeptide of type I procollagen, and car boxyterminal telopeptide region of type I collagen, respectively. Seru m thyrotropin, free T-4 and free T-3 were measured by time-resolved fl uoroimmunoassays (Delfia(R)). Serum carboxyterminal telopeptide region of type I collagen concentrations of thyroid carcinoma patients were significantly higher than those of the controls (p = 0.0012). Serum ca rboxyterminal propeptide of type I procollagen concentrations did not differ significantly between the patients and controls (p = 0.85). Sig nificant associations between age or physical activity, and carboxyter minal propeptide of type I procollagen or carboxyterminal telopeptide region of type I collagen were found in the controls, but not in the p atients. Thyrotropin, free T-4 or free T-3 were not significantly asso ciated with carboxyterminal propeptide of type I procollagen or carbox yterminal telopeptide region of type I collagen in either the control or patient group. From these results it is concluded that long-term su ppressive thyroxine treatment seems to accelerate bone degradation, bu t not bone formation, and therefore carries a risk for osteoporosis. T hyrotropin or free thyroid hormones were not able to predict the accel erated bone degradation within the patient group. The normal regulatio n of bone metabolism is altered during long-term. high dose thyroxine treatment, as evidenced by the fact that the effects of age and physic al activity were not seen in patients. Differentiated thyroid cancer i s generally diagnosed in young people, and patients may receive high-d ose thyroxine treatment for decades. Problems due to side effects, lik e accelerated bone degradation, may arise gradually. This risk should be taken into account in the management of thyroid carcinoma patients.