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POSSIBLE RTH-BETA?    12/12/15

Last Updated: · Doctors

QUESTION- I recently saw a 68-year-old female who started experiencing shortness of breath and fatigue.  She was evaluated by primary care provider who found her to be in atrial fibrillation with rapid ventricular rate.  She was started on anticoagulation and metoprolol.  Echocardiogram revealed ejection fraction 308 with mild left aortic enlargement and wall motion abnormalities and severe left atrial enlargement.  Thyroid panel revealed TSH 3.4 mIU/L, free T4 of 2.0 ng/dL (normal 0.9 to 1.7) and free T3 elevated at 3.7 (normal 2.0 to 3.5 pg/mL).  Repeat TSH was elevated at 4.75 with free T4 normal at 1.6 mg/dL but free T3 still elevated at 3.6 pg/mL.

This is her thyroid panel (over the last 2 months):

12/15   11/15    10/15

TSH                  4.7      4.75      3.44  (0.27-4.29 mIU/L)

Free T4          1.5       1.6         2.0   (0.9-1.7 ng/dl)

Free T4D          2.3                          (0.8-2.0 pg/dl)

FT3                  3.5       3.6        3.7  (2.0-3.5 pg/dl)

TSI                    <1.0

Alpha subunit of pituitary 0.7.

No previous thyroid test available. No known family history of thyroid problems.

Is this most likely resistance to thyroid hormone?

Should I have family members tested vs. genetic testing?

Cardiologist wants to cardiovert but would like to thyroid function to normalize before cardioverting. If this is resistance this may not happen and should we just continue beta blocker? Thank you. Hammad Hussain, MD, ECNU, CCD, CDE, Rochester, MN

RESPONSE–It is possible that the mild elevation of both free T4 and T3 are due to resistance to thyroid hormone (RTH) of the beta type,. However, this will need confirmation by THRB gene sequencing. Quest laboratories will do the gene analysis.

You are correct in your conclusion that  if she had RTH-beta you just continue beta blocker and further, the cardiologist should proceed with  cardioversion with her current tests will not reflect thyrotoxicosis. Hope this helps, Samuel Refetoff, M.D.