Hypothyroid, but no antibodies?!

[Hannah1986]

Hi,
For the past year and a half, I've been having some very strange symptoms. About a year ago, I had a very severe bout of mononucleosis that lasted for months on end.   After I recovered, the fatigue never went away, and I gained a significant amount of weight which i was not able to lose despite diet and exercise. I had problems with very strange muscle weakness while exercising, and I also developed a huge problem with my concentration and memory...i am a student so this became a major issue in my life. Autoimmune disorders run in my family, so on a hunch, I had my thyroid tested. It turns out I am very slightly hypothyroid. My TSH before I had mono was 2.1. It is now 5.4, and my T4 is borderline low. The doctors originally told me I had an early case of Hashimoto's, but when they tested my blood for antibodies, I was negative. My question is, what could be causing this hypothyroidism, if i don't have hashimoto's? Isn't that the most common cause? Could I still have Hashimoto's even without any antibodies? or could my thyroid have been somehow damaged by epstein-barr infection? Nobody seems to have any answers for me.
Thanks,
Hannah

[Pearlie]

My Doctor wants to put me on 25mcg synthroid because my T-4 level is 0.7and my TSH is 0.86. My prolactin level is 22.7. I do not have any symptoms of hypothyroidism and I have always had a little prolactinemia. I am 38 y.o.female. Is this appropriate treatment?

[Mark Lupo, M.D.]

hashi is the most common cause -- about 10% of hashi patients may have normal antibody levels.  In these cases I usually repeat the TSH in 6 weeks and if still elevated consider treatment. Also, an experienced thyroid ultrasonographer can detect subtle inflammation in the thyroid which may also suggest hashi in the absence of antibodies.