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Central Hypothyroidism?

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Question

I am presenting a patient who I need some advice as to how I can make a diagnosis. A 66 year old female with h/o primary hypothyroidism (TSH:7.103 in 6/01) started on synthroid 50 mcg/ day and repeat TSH was 3.318 on 8/01. Pt then was lost to f/u and the next TSH available was :12/31/02 : 0.00, pt was taken off her LT4 and repeat TSH’s was : 2/28/03 : TSH :0.02 (0.34 – 5.00) 6/4/03) TSH :0.04 (0.34- 5.00) 10/6/03: TSH 0.00 (0.34 -5.00) 10/14/03: I131 uptake at 24 hours: 8.9% 12/03/03: TSH: 0.151 (0.350-5.5) FT4: 0.86 (0.89 – 1.8) FT3: 2.9 (2.3 – 4.2) Pt ‘s only complaints are dry itchy skin and low energy. Medications: Paxil 12.5 mg/day, lasix 20mg, provera 5mg, estrogen patch, prevacid, relfen, centrum silver and cod liver oil capsules. Past medical history is only significant for hypertension, depression, GERD. Her physical exam is unremarkable.My working diagnosis was Central hypothyroidism.In order to evaluate the pituitary the foll tests were asked for. 1. MRI of pituitary: Normal with no masses 2. FSH: 14.8 (PT is on HRT) 3. LH: 10.3 4. Prolactin: 4.8 5. IGF :108 6. Cortisol (AM) 12.8) In summary a 66 year old female with central hypothyroidism and normal pituitary imaging. 1. Is a TRH test indicated here. 2. Could her hypothyroidism be secondary to a hypothalamic etiology. Thank you,

Bindubal Balan, MD

Response

Although the natural first assumption is that she has only central hypothyroidism, itseems to me that the situation is probably more complicated than that. She began with an elevated TSH, which is possible in central hypothyroidism, but it responded to treatment, she has no sign of tumor, and the rest of the evaluation is negative. Further, without treatment , her hormone levels are near normal and her RAIU is near normal (depending on Iodine supply). We do not know findings by thyroid US or antibody tests, which should be evaluated. TRH testing would be of interest, if a good response occurred,but it often does not tell more than the basal TSH.It is rare for the TSH to be 0.00 in any situation except suppression by elevated thyroid hormone, or some sort of TSH testing error. I would guess that she has some hypothalamic/pituitary problem making her TSH set point low and easily suppressed, and this has been reported in elderly patients. This is also hard to prove. I think she also was exposed to higher than normal levels of T4 at some point so that her pituitarywas suppressed. I would follow her without treatment at this point and see if her TSH gradually return s toward normal. It would be of interest to measure TSH in a different lab to rule out some error due to heterophile antibodies. The duration of suppression of her TSH while off T4 is truly prolonged , but not incompatible with this evaluation of the problem. If the evaluation provides no further avenues of understanding, and hormone levels remain at the current level, mild T4 supplementation could be reinstituted. Please let us know any follow-up.

Leslie J De Groot,MD