Thyroid Hormone Resistance vs. TSH-OMA ?


Question

I wonder if I might get an opinion on what you would do next: 74 year old male had routine physical exam and labs done by his primary care physician in May. As part of laboratory panel a TSH and free T4 were done. The TSH was 1.64 (0.4-4.0) and the free T4 was 2.03 (0.68-1.76). These were repeated 7/8/04. TSH was 1.77, free T4 was 1.98 and T3 was 149(58-184). Patient then sent to endocrinology for evaluation. Per history he has been well and specifically denied any symptoms suggestive of hyperthyroidism. He has a daughter with a history of hypothyroidism. On examination his pulse was 68, EOMI, no lid lag, visual fields were intact to confrontation, thyroid was without goiter, nodules or bruits, no hyperreflexia or tremor was present. Labs were repeated 7/29/04 with TSH 1.60 (0.4-4.0), free T4 2.24 (0.68-1.76) and T3 134 (58-184), alpha subunit was 2.2ng/ml (normal < 1.0).

Thyroid hormone resistance syndrome vs TSH secreting adenoma vs other?? What would be recommended as the next step. T3 suppresion test? Get TFTs on family members? MRI?

K K, M.D. Fontana, CA 92335

Response

Dear Dr. K,

Thank you for your recent email. Dr. DeGroot has asked me to respond. The patient you describe appears to have elevated free T4 with normal TSH and normal T3 levels. The absence of an elevated TSH makes the diagnosis of RTH or TSHoma unlikely, but does not completely rule it out. It is possible that there is a binding protein abnormality or an antibody that is interfering with the free T4 assay used (or conversely there is something interfering with the TSH measurement). Given the elevated alpha subunit at this point I would agree that an MRI of the pituitary should be done. Your suggestion to get blood tests on other family members is a reasonable approach. If you and the family are interested we can evaluate the thyroid function along with binding proteins in our laboratory at the University of Chicago. While there would be no charge for the blood tests, the family members would be responsible for the expenses of phlebotomy and shipping of the blood. I have attached instructions for shipping as well as a consent form that should be signed by all the subjects. We should obtain blood from the propositus as well as his children and their spouses for starters. If other family members have a similar thyroid phenotype genetic testing may then be performed.

Roy E. Weiss, MD, PhD, FACP rweiss@medicine.bsd.uchicago.edu