Investigators have allayed concerns that long-term levothyroxine (L-T4) therapy could have an adverse effect on the bone health of thyroid cancer patients.
"Untreated hyperthyroidism and treatment with high doses of thyroid hormone are associated with osteoporosis," observe Caroline Heijckmann (University Hospital Maastricht, The Netherlands) and colleagues.
"However, their effect on bone turnover, their contribution to bone mineral density (BMD) in the context of other clinical risk factors for osteoporosis and the prevalence of vertebral fractures is not well documented."
For their cross-sectional study, the researchers examined 59 patients who were receiving L-T4 therapy for differentiated thyroid carcinoma (DTC). The mean dose of L-T4 was 2.2 µg/kg/day.
Dual X-ray absorptiometry (DXA) was performed to measure BMD of the hip, and to obtain lateral pictures of the lumbar and thoracic vertebrae. Bone resorption was assessed by measuring levels of C-telepeptides of type I collagen (ICTP), and bone formation by procollagen type I N-propeptide (PINP). Clinical risk factors for osteoporosis were also evaluated using a questionnaire.
The results showed that the BMD scores among the thyroid cancer patients were comparable to those in a reference group of men and women from the National Health and Nutrition Examination Survey III. Moreover, this was the case even after more than 10 years of L-T4 therapy. Importantly, only four patients experienced a vertebral fracture over this time.
Levels of ICTP were significantly higher in patients with DTC than in age-matched control individuals, but PINP levels were comparable in the two groups. Speculating as to why this change in balance between bone resorption and formation did not lead to long-term bone loss, the researchers suggest that the increase in bone resorption may not have been substantial enough to affect BMD.
"We conclude that patients with well-differentiated thyroid carcinoma are not at increased risk of developing low bone mass nor have a higher prevalence of vertebral fracture, at least when treated with relatively low doses of L-T4," the study authors write in the European Journal of Endocrinology.
"We suggest that specific screening for osteoporosis in this patient group is therefore not recommended, other than on the basis of the known clinical risk factors," they say.
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