TSH fluctuation and persistent tachycardia

[Khitchin]

Thank you very much, doctor, for taking my question.

I am a 24-year-old female and have been experiencing many symptoms for the past couple of years, the most disconcerting of which are sleep problems, weight gain, anxiety/depression, memory loss, and profuse sweating.  I recently learned that I have been in tachycardia, which would explain the sudden sweating and heat intolerance.  It has been a month now since I realized that I've been above average (my resting bpm is almost consistently about 100 and escalates up to 170 with casual walking).  All of my ECGs and echocardiograms showed no congenital defects and 71% pumping volume.  I am scheduled to see an electrocardiologist in three weeks.

I went to the ER a few weeks ago and had a TSH of 8.55 with 0.8 total T3 and 2.8 free T4. One week after my ER visit, I saw an endocrinologist who tested TSH, T3, and TPO-antibodies.  TSH had dropped to 1.75 and free T3 was "normal," and TPOab was <35.  We are currently awaiting test results for TSI-antibodies, celiac disease (for persistent digestive problems), and pheochromocytomas.  If there is no cause for my symptoms found of these tests, my endocrinologist doesn't know what to do.  Hypothyroid runs rampant in the women of my family, but my endocrinologist says that my thyroid is fine, nor does he believe my pituitary is the cause.  

Aside from lab error, what would cause my TSH to fluctuate so widely (8.55 to 1.75) within just one week?

In terms of endocrinology, is there any other avenue to explore to explain the majority of my symptoms, but primarily the tachycardia?  

Could the pituitary, hypothalamus, or HPT axis be to blame for this?

I really appreciate any thoughts you are able to provide!

[Mark Lupo, M.D.]

The TSH levels may have fluctuated due to "non-thyroid illness" - in other words, the stress of the other condition threw-off the thyroid levels.  These TSH levels would not usually suggest a thyroid problem as the cause of tachycardia.  Checking for pheo is appropriate - otherwise, not likely to be endocrine related in most cases.  keep working with the cardiologist to get to the bottom of it - the electrophys evaluation is a good idea.

[Khitchin]

Another note: I have been on 25 mg metoprolol to control my heart rate, but I haven't seen a significant difference.  My cardiologist did not want to increase the dosage because my bp was low-normal, although now, it seems to be even higher than before.