Jacqueline Jonklaas: Researching Better Treatments for Thyroid Deficiencies
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About 5 percent of the U.S. population has hypothyroidism, which occurs when the thyroid gland does not produce enough thyroid hormone to meet the body’s needs. Without enough of this hormone, the body’s processes often begin to slow down.
Standard current thyroid therapy for this condition, as well as those whose thyroid has been surgically removed or disabled by radioactive iodine, is hormone replacement. This is achieved most commonly with the medication levothyroxine (LT4), which is administered to replace thyroxine (T4). In some cases combination therapy is used, to replace also the second thyroid-secreted hormone, triiodothyronine (T3). Thus far, trials evaluating the combination therapy have failed to demonstrate any consistent advantage over the T4 therapy alone.
However, work being done by Jacqueline Jonklaas, MD, PhD, assistant professor of Endocrinology and Medicine in GUMC’s Department of Medicine, may change how this condition is treated. Jonklaas led a four-year study of Georgetown patients – 37 women and 13 men, ages 18 to 65 – all with normal thyroid function but scheduled for total thyroidectomy for goiter, benign nodular disease, suspected thyroid cancer or known thyroid cancer. The study’s objective was to determine whether T3 levels in patients treated with T4 therapy alone were truly lower than native thyroid function in the same patients. Following thyroidectomy, patients were prescribed LT4. All were maintained on a brand name medication (generic medications have different inert ingredients that can affect absorption). By the end of the study, there were no significant decreases in T3 concentrations in patients receiving LT4 therapy compared with their prethyroidectomy T3 levels, a result suggesting that it is not necessary to administer T3 to maintain serum T3 values at their endogenous prethyroidectomy levels.
Dr. Jonklaas points out that T3, with its short half-life, requires patients to take medication two or three times a day, making it difficult to maintain steady levels and increasing possible side effects; T4 therapy is administered only once a day. She notes, however, that her study indicated that there may be a small subset of patients who are unable to make T3 as effectively as other patients from T4 replacement alone.
“They may have certain genes that affect the ability to generate sufficient T3 for some tissues. Future studies could look at this smaller number of patients to see if they might benefit from combination therapy,” says Dr. Jonklaas.
There is also anecdotal information that some patients report feeling better on combination therapy. Factors such as memory or mood and well-being were not a part of this current study, since participants had undergone major surgery that could have had independent subjective effects.
Since hypothyroidism usually affects women, research such as Dr. Jonklaas can have a significant impact on women’s health in particular. Both hypothyroidism and thyroid cancer are more prevalent in women.
“Optimization of therapy for hypothyroidism is critical not only for the health of the individual, but also for optimization of fertility and pregnancy outcomes,” says Dr. Jonklaas.
Other studies are underway. Working with other institutions, Dr. Jonklaas is examining the impact of various treatments for thyroid cancer; current thyroid cancer management including thyroid surgery, radioactive iodine treatment, and the use of thyroid hormones to suppress thyroid stimulating hormone (TSH) levels. Dr. Jonklaas is also studying ways to minimize the side effects of radioactive iodine, which is a valuable tool for thyroid cancer treatment.
For more information or to refer a patient for thyroid treatment, please call the Georgetown University Hospital Physician Access line at 202-342-3300 or 800-442-4200.
By Eve Katz, PhD, excerpted from the Summer 2008 issue of Georgetown Physician Update
