Thyroid hormone therapy and the skeleton

Dr. Repas does not need my help in responding to the flurry of comments he has received following his recent blogs about thyroid hormone therapy. However there is one issue that was not raised by any of the respondents — the adverse bone effects of over-medication with thyroid HT.

The effects of thyroxine on the skeleton are very similar to those of parathyroid hormone. In fact, one of von Recklinghausen’s original cases of osteitis fibrosa was not due to primary hyperparathyroidism but resulted from the Jod-Basedow phenomenon — development of hyperthyroidism from over-replacement of iodine in communities where the available iodine was limited.

There are many published guidelines on the evaluation and management of osteoporosis and almost without exception they recommend measurement of thyroid function in all patients with a low bone density or osteoporosis.

This is much more of an issue in patients taking thyroid HT than it is in patients with endogenous hyperthyroidism. In those with endogenous hyperthyroidism the symptoms are generally not subtle and the patient seeks medical attention before too long.

In stark contrast, patients receiving only minimally excessive thyroid HT or supplements feel very well and do not seek medical attention. I see these patients when they present with markedly low bone density without obvious cause and all too often they present at a relatively young age with multiple vertebral fractures.

It is essential to monitor the thyroid-stimulating hormone on a regular basis (at least once a year) and maintain levels within the normal range, preferably in the upper half of the reference interval. Patients taking non-FDA-approved therapies may need to be monitored more often because of unrecognized variability in the tablets.

I have run into many problems when attempting to lower the dose in patients mildly “over-dosed” because they do feel well and do not feel as well when the dose is lowered. It is easier to be aggressive in patients who have already sustained fractures and are symptomatic but much more difficult in healthy patients with “abnormal” numbers, not diseases. Patients are wonderful! Patience is a virtue!