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Thyroid Cyst, and Mild Hyperthyroidism, in Pregnancy

Last Updated: · Doctors


I am an endocrinologist in Salisbury, NC. I saw a 37yo WF in her first trimester with a distant history of solitary thyroid cyst. The pt was clinically euthyroid. On exam she had a readily palpable 3+ cm R sided thyroid nodule. Her tsh was <0.003 and FT4 was 1.00 (upper limit of nl 1.54).Old records requested. Could only retrieve FNA x 2 done in ~1994 and the second done 1995. The first was read as benign and the second was without sig cellularity butwithout any suspicious findings. Apparently an US had been done but not available. No old labs either. My assessment: subclinical thyrotoxicosis, solitary thyroid cyst, recurrence probable, pregnancy.

My question: Now pt is in her second trimester with stable thyroid indices. I have not recommended thionamides given her clinically euthyroid status and her mild biochemical levels. However, I wonder whether I should re-biopsy the cyst now. I have not thus far biopsied because of the fact of her earlier benign report and because of my concern for the cyst/nodule now being autonomous and that biopsy would lead to misleading results.I cannot do an I123 scan on her now. Do you think this management plan is reasonable? I have advised her to strongly consider surgical excision in an elective fashion in the postpartum setting.


Carey Robar


The situation is surely complicated. It is unlikely that the TSH suppression is due just to the normal high hCG of early pregnancy. It is also surprising that it could be due to a thyroid cyst. So one wonders about a functional thyroid lesion (probably adenoma) associated with the prior cyst, or Graves disease, since she does not have hyperemesis syndrome.

I would recheck TSH, freeT4 and T3 to be certain of the degree of hyperthyroidism. I would also do an US, and anti-TPO and anti-TG antibodies, as well as TSAb.

Although one can argue the merits, I would trend to treat the hyperthyroidism with anti-thyroid drugs, even if mild. If the US shows one lesion with a cystic and solid component, it would be of interest to biopsy the solid area. Fortunately the chance of malignancy would be small. If the an t ibodies are positive, it would suggest that the cyst/adenoma is incidental, and that the patient has mild Graves' Disease. Let us know what further develops.

L De Groot, MD