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Hashimoto’s, Transient Hypothyroidism, and an Elevated RAIU

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Question

May I get your opinion on the following case: 22 year old woman with presents to her primary provider with complaints of amenorrhea times 6 months. Additional concerns include cold intolerance, dry skin, hair loss and an 18lb weight gain over the past year. In March of this year TSH 2.54.. On 8/14/02 TSH 52.43, Free T4 0.62 (nl .68-1.76). On 9/9/02 TSH 30.61, free T4 0.69, T3 118, TPO ab 972. Primary provider orders thyroid uptake and scan which are completed on 9/12/02, prior to her evaluation in the endocrine clinic 9/16/02. The scan shows a diffuse goiter. The 6 hour uptake is 32%. In endocrine clinic the above history is obtained.

Physical examination is notable only for a diffuse goiter about 2 times normal size, which is non-tender. Can we explain this mixture of findings based on an acquired defect > of iodide organification secondary to TPO ab inhibition of thyroid peroxidase? If not, what might be the cause of the high uptake at the same time as the high TSH and low free T4 levels. Would you not just go ahead and put her on L-T4 replacement therapy?

Thank-you so much for your assistance,

Karen Kartun, M.D.
Kaiser Permanente Division of Endocrinology
9985 Sierra Avenue
Fontana, CA 92335

Response 1

This patient clearly has autoimmune thyroid disease as shown by the positive TPO antibodies. There has been a very rapid change in thyroid function, from a normal TSH to a value of 50 in 6 months and then a rapid fall, with only barely reduced T4 levels at the peak of TSH and a normal T4 on the last value we are given. Although TPO antibodies may inhibit TPO enzyme activity in vitro, these data are controversial and there is no in vivo evidence to support this type of action. For instance TPO antibodies are transferred across the placenta yet the babies of such mothers with high TPO antibodies have normal thyroid function. Goitrous autoimmune hypothyroidism with an elevated TSH is a known cause of increased radioiodine uptake (1). I suspect that this is the diagnosis here and the pattern of thyroid function fits with a recovering phase of silent thyoiditis in such a gland. Whether the increased uptake is solely mediated by the elevated TSH or is due to coincidental thyroid stimulating antibodies, which occur in some patients, could only be assessed by measuring these antibodies but I do not think this test is strictly necessary. I would simply ensure that the patient is not taking iodine supplements intermittently, and monitor thyroid function regularly, say every 3- 4 weeks; the latest T4 level is normal and therefore there is no need to start thyroxine until the pattern of illness shows this is needed. If normal thyroid function resumes, regular followup will be required. 1. McDougall IR, Cavalieri RR. In vivo radionuclide tests and imaging. In Werner and Ingbar’s The Thyroid. 8th edition Eds Braverman LE, Utiger RD, Lippincott, Philadelphia pp355-375

Dr. Anthony Weetman

Response 2

May another contributor note that the last values fit with subclinical hypothyroidism, and some practitioners – (including this one) would feel safer starting replacement T4 at this time.

L De Groot, MD