Very low TSH, no symptoms

[ellied1]

     Two blood tests in the last 3 months have shown my TSH going from 0.05 to 0.04, and my family doctor is cutting levothyroxine from 112 mcg to 100 mcg daily. Nine months ago, my TSH was at 0.76.  That was before surgery to remove a 24-cm (benign!) ovarian tumor, and complete hysterectomy.  From the months before surgery through the month after, I lost about 35 pounds, then stablized.  Since surgery, I've begun walking briskly for about a half-hour a day.  This kind of consistent exercise is new for me, at least in the last 25 years.
     I'm 70 years old.  I was diagnosed with Graves about 20 years ago, and have been taking levothyroxine since a few months after radioactive iodine treatment.  I was relatively stable as to dose for quite a few years, but have had more adjustments in recent years, all downward.
     I can remember fairly clearly the symptoms when I was acutely hyperthyroid.  I'm experiencing nothing like that now.  My resting heart rate ranges from mid-50's to low 60's.  My muscle tone is good, no weakness.  I sleep as well as I ever did, and if anything I'm more intolerant of cold than heat.
     The only other medication I take is 10mg enalapril daily.  Oh, and 800mg of calcium and 1000 iu of vitamin D.
     So I'm really confused about what's happening and WHY.  

[ellied1]

Thank you so much --- I do hate not understanding what's going on, but I will try to be patient until the next blood test!      

[Mark Lupo, M.D.]

This is not clear why you're TSH is low on a similar dose of levothyroxine but I agree with decreasing the dose and rechecking and 2-3 months.  If there is continued decreased requirements in an investigation into production of thyroid hormone from your thyroid (very unlikely) would be necessary.