L-thyroxin treatment and post-menopausal osteoporosis: relevance of the risk profile present in clinical history.

Aim: Nodular thyroid disease and osteoporosis share some common factors such as: 1) elevated frequency in the general population; 2) major prevalence in the female sex; 2) incidence proportional to the age. There is a wide debate in literature regarding the real impact of chronic treatment with L-thyroxin (LT4) on the bone mineral density (BMD), especially in post-menopausal women. The aim of this study was to undertake to evaluate the effects of LT4 administration for the treatment of normo-functioning nodular thyroid disease on the BMD in post-menopausal women after one year of continuative treatment. Particular attention was paid in examining the role of some anamnestic risk factors for osteoporosis on the clinical response.

Methods: Ninety nine postmenopausal women of age comprised between 50 and 56 years were examined before and after 1 year of therapy with a fixed dose of LT4 for the treatment of nodular thyroid disease by monitoring the following laboratory parameters: thyroid stimulating hormone (TSH), FT4, FT3, antithyroglobulin antibodies [AbTG], hyroid peroxidase antibodies [AbTPO], serum calcium and alkaline phosphatase levels and 24-urinary excretion of calcium and hydroxyproline. Bone mineral density (BMD) was measured by dual X-ray absorptiometry of the lumbar vertebrae.

Results: The results of this study showed that the patients on treatment with LT4 have a slight, but significant reduction of the BMD after 1 year of treatment, associated with increased serum levels of alkaline phosphatase and urinary excretion of hydroxyproline. Comparison between patients with unsuppressed (group A) or suppressed (group B) TSH following LT4 treatment showed that group B patients had significantly lower BMD. The following risk factors influenced, in a statistically significant manner, the BMD: 1) Body Mass Index <19 kg/m(2); 2) the onset of menarche after the age of 15 years; 3) history positive for period of amenorrhoea; 4) nulliparity; 5) surgical menopause; 6) lack of hormonal replacement therapy; and 7) presence of auto-antibodies against thyroid antigens.

Conclusion: LT4 treatment in postmenopausal women reduced significantly the BMD. This treatment should be therefore prescribed with caution in this condition and particularly when the following risk factors are present: surgically driven menopause, constitutional thinness, history of nulliparity, absence of hormonal treatment, positive history of secondary amenorrhoea during the reproductive age, autoimmune thyroid disease and delayed menarche.