Long-term treatment with supraphysiological doses of thyroid hormone in affective disorders — effects on bone mineral density

Abstract

To investigate the long-term effects of supraphysiological, TSH suppressive doses of levothyroxine (TSDL) on bone mineral density (BMD) in patients with affective disorders during an average treatment duration of 69 months. In 22 patients, BMD of the spine (lumbar vertebrae L1-4) and femur (femoral neck) was measured by dual energy X-ray absorptiometry (DXA). Forty (40) measurements from the prior study and 48 new follow-up measurements were included. BMD was expressed as Z-scores as a population standard reference. We used a linear mixed model to investigate the duration of TSDL as an explanatory factor for change in BMD compared to an age and gender matched reference population. We found no significant differences in bone loss between the study and the reference population. The estimated non-significant decrease in Z-score compared to the reference population found was: a) lumbar spine (L1-4): -0.00069/month (p=0.9759) b) neck region of femur: -0.01405/month (p=0.4436). We did not find the factors age, thyroxine-dose or postmenopausal state as predictors for a decline in BMD. Small sample size, no bone density assessment prior to treatment with TSDL, no patient control group with mood disorders who did not receive TSDL, variable bone density follow-up intervals. This study did not demonstrate evidence that long-term treatment of affectively ill patients with TSDL accelerates loss of BMD compared to an age- and gender-matched reference population.