Clinical Thyroidology® for the Public

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THYROID CANCER
Bone density testing intervals in TSH suppression for thyroid cancer

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BACKGROUND
Thyroid cancers such as papillary and follicular carcinoma account for approximately 90% of all cases of thyroid cancer. Initial therapy for thyroid cancer includes surgery to remove the thyroid. In higher risk thyroid cancers, surgery is followed by radioactive iodine therapy. Thyroid hormone therapy is begun after surgery in all cancers where the entire thyroid has been removed (total thyroidectomy) and in many where only a lobe was removed (lobectomy). In patients where the cancer is at high risk for a recurrence, high doses of thyroid hormone are often prescribed to turn off TSH levels (TSH suppression therapy). Since TSH stimulates thyroid cell growth, long-term suppression of TSH, particularly in more advanced cases of thyroid cancer, may decrease the risk of cancer recurrence. However, the benefit of TSH suppression must be balanced with the risks of doing so, which include a higher risk of osteoporosis.

A bone mineral density (BMD) test is used to diagnose osteoporosis and predict one’s risk for bone fractures. BMD uses the T-score to compare a patient’s bone density to the average bone density of young, healthy adults of the same gender. The lower the T-score, the higher the risk of fracture. Specifically, a T-score between -1.0 and -2.5 is diagnostic of low bone mass or osteopenia, and a T-score of -2.5 or below is diagnostic of osteoporosis. TSH suppression during the treatment of thyroid cancer can lead to a decrease in BMD, especially in postmenopausal women. BMD testing is recommended ever 2 years in patients at risk for developing osteoporosis or to monitor those on treatment for osteoporosis. However, there are no guidelines to help determine the frequency of BMD testing in thyroid cancer patients who require TSH suppression therapy. In the present study, the authors evaluate the progression to osteoporosis and the timing of BMD testing in thyroid cancer patients on TSH suppression.

THE FULL ARTICLE TITLE
Park H et al 2022. Bone‐density testing interval and transition to osteoporosis in differentiated thyroid carcinoma patients on TSH suppression therapy. Clin Endocrinol 97:130–136.

SUMMARY OF THE STUDY
The authors studied 658 thyroid cancer patients on TSH suppression therapy who underwent BMD testing more than twice at the Samsung Medical Centre in Korea between January 2007 and January 2020 . This thyroid cancer group was matched with a group of healthy women without thyroid cancer to compare the timing of BMD tests between thyroid cancer and non-thyroid cancer patients. Participants were divided into four groups based on their baseline T-score: Normal [-1.00 or higher], mild osteopenia [-1.01 to 1.49] moderate osteopenia [-1.50 to -1.99] and severe osteopenia [-2.00 to -2.49]. The 10% of patients in each group who progressed to osteoporosis were analyzed in the hope that this measure could guide future recommendations for BMD testing intervals in thyroid cancer patients. The authors also examined other general factors associated with worsening BMD in the study population.

In the thyroid cancer group, 14.7% of patients developed osteoporosis during the follow-up period while 13.6% of patients in the non-thyroid cancer developed osteoporosis. The estimated BMD testing interval for 10% of patients who developed osteoporosis in the thyroid cancer group compared to the non-thyroid cancer group was 7.1 versus 8.2 years for patients with initially mild osteopenia, 5.4 versus 4.8 years for those with moderate osteopenia, and 1.3 versus 1.1 years for those with severe osteopenia. Thus, the progression rate from osteopenia to osteoporosis was statistically no different between the two groups. However, baseline t-score and duration of TSH suppression were independent risk factors for the development of osteoporosis in the thyroid cancer group.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that, despite a trend towards more rapid progression to osteoporosis in thyroid cancer patients on TSH suppression therapy, there was no significant difference compared to patients not on thyroid hormone over the duration of the study. This is important for patients and physicians to show that requiring TSH suppression due to advanced thyroid cancer does not have a major adverse effect on bones. This also suggests that more frequent BMD testing in not indicated in thyroid cancer patients.

Since the appropriate testing interval was the same for thyroid cancer patients on TSH suppression as non-thyroid cancer patients, a patient’s baseline T-score should to determine the interval between tests.

— Phillip Segal, MD

ABBREVIATIONS & DEFINITIONS

Bone mineral density (BMD): measurement of bone strength that is used to diagnose osteoporosis and predict one’s risk for bone fractures. BMD uses the T-score to compare a patient’s bone density to the average bone density of young, healthy adults of the same gender. The lower the T-score, the higher the risk of fracture. Specifically, a T-score between -1.0 and -2.5 is diagnostic of low bone mass or osteopenia, and a T-score of -2.5 or below is diagnostic of osteoporosis.

Osteoporosis: a decrease in bone mineral density in which the individual is at a significantly increased risk for fractures with little or no trauma or force. This occurs with a bone mineral density T score of >-2.5. The areas at highest risk for osteoporotic fractures are the wrist, spine and hip.

Osteopenia: a decrease in bone mineral density in which the individual is at a slightly increased risk for fractures with little or no trauma or force. This occurs with a bone mineral density T score between -1 and -2.5.

TSH: thyroid stimulating hormone — produced by the pituitary gland that regulates thyroid function; also the best screening test to determine if the thyroid is functioning normally.