NORMALIZATION OF SERUM THYROTROPIN BY MEANS OF RADIOIODINE TREATMENT IN SUBCLINICAL HYPERTHYROIDISM - EFFECT ON BONE LOSS IN POSTMENOPAUSALWOMEN

BACKGROUND Patients with subclinical hyperthyroidism (reduced serum TS H and normal free T4 and T3 concentrations) have slightly increased bo ne turn-over and might have reduced bone mass, especially among postme nopausal women (due to concomitantly reduced oestrogen production), as also seen during suppressive L-T4 treatment, OBJECTIVE We have evalua ted whether normalization of serum TSH using radioiodine treatment (RA I) in postmenopausal women with a nodular goitre and subclinical hyper thyroidism, protects against bone loss? DESIGN Prospective, non-random ized study, out-patients, 2 years follow-up, PATIENTS Postmenopausal w omen with a nodular goitre, biochemically subclinical hyperthyroidism (TSH < 0.2 mU/l, and signs of a growing goitre or compression symptoms , Sixteen were treated with RAI (median dose 555 MBq) (+RAI), whereas 12 were followed without treatment (-RAI), MEASUREMENTS Serum TSH (thi rd generation technology), free T4 and T3 indices, and bone mass (BMD) as measured by Dual Photon Absorptiometry (4 in each group) (only spi ne) or Dual X-ray Absorptiometry (DEXA) (both spine and hip), were mea sured yearly for up to 2 years, RESULTS The two groups did not differ regarding age, thyroid hormone parameters, and absolute levels of BMD at spine and hip. RAI resulted in normalization of TSH in all 16 women , and FT4I as well as FT3I decreased to 78% after one year (P < 0.01). These parameters did not change in the untreated group, thus serum TS H remained reduced, BMD at the spine tended to increase (n.s.) after R AI to (median) 101.9% after one year, and 101.5% after 2 years, In con trast the -RAI group experienced a continued fall in BMD to 97.3% afte r one year, and 95.5% after 2 years, both reduced as compared to the RAI group (P < 0.02), BMD of the hip also increased after RAI, to 102. 3% after one year, and 101.7% after 2 years. In contrast BMD in the -R AI group decreased to 94.8% after one year, and 98.0% after 2 years, b oth lower than in the +RAI group (P < 0.01). CONCLUSIONS Subclinical h yperthyroidism due to a nodular goitre in postmenopausal women resulte d in a continued loss of bone mass of about 2% per year. Radioiodine t reatment resulting in normalization of serum TSH prevented this contin ued bone loss for at least 2 years. Our study supports earlier interve ntion in such patients.