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QUESTION--I would be thankful if you could kindly guide me on this clinical situation I come across so often.

Patients of various age groups are frequently referred with persistent subclinical hyperthyroidism. TSH suppression can be mild or less than 0.2 mIU/l. Patients may be asymptomatic or having symptoms that may or may not be secondary to subclinical hyperthyroidism.

On many occasions I do not find any underlying cause, thyroid antibodies including TSH receptor antibodies are negative, pertechnetate thyroid uptake scans are normal with no hyper functioning nodules are demonstrated.

How should these patients be managed. Which of these patients are candidates for antithyroid medications. How long should they be treated.

Young or old, should these patients have bone densitometry scan in order to decide about treatment.

Is there any role of urine iodine measurement and replacement if found low rather than initiating patients on antithyroid patients first or can have combined treatment with antithyroid medication and iodine replacement. What is the dose for iodine replacement, or patients can only have fortified iodine food products.

Medical literature I read recommend treatment of the underlying cause depending upon patients age and severity of TSH suppression, cardiovascular and bone health. But they do not say anything what to do if no underlying cause is found.

Many thanks for your response.  Dr S Aziz

RESONSE--It could take a search to figure this all out, but I doubt that your patients have a serious medical problem. Lacking a clear diagnosis, or evidence of a problem, I would purse diagnosis or exclusion of disease, and not treatment.
1 Is the finding consistent and reproducible in the patient?. Is it reproducible in a different lab?  IS there any prior personal or family history that suggests a diagnosis?
2.Values of TSH of 0.2 or 0.3uU/ml in the absence  of elevated fT4 and  elevated fT3 and without symptoms  are probably close enough to normal to ignore, and would be considered normal by some MDs, and in pregnant women..
3.Does your lab have actual data  on 100-200 ”normal” assays for TSH, fT4 and fT3,  using their exact technique, for non-pregnant adult women and men for you to use as the local gold standards?

4. you have presumably already checked TG,TPO  and TSHR antibodies., and probably ruled out autonomous thyroid nodules, and the thyroid is not enlarged, nodular  or tender.
5. If all of these approaches fail, next check RAIU using iodine isotope to see if it is suppressed. If not, that would rule out most causes of true functional hyperthyroidism.

6.Some outliers remain. TSHoma (alpha subunit and MRI), excess iodine (check urinary iodine), surreptitious ingestion of thyroid hormone such as T3 in a diet supplement, Hashimoto’s but would expect at least an enlarged thyroid, SAT (unlikely but one can check elevated T4, CRP, absent RAIU, etc), amiodarone, hydatiform mole, IL-2 or interferon treatment, Campath treatment
If none of these fall out, it may be time to start collecting cases and making a real scientific study. Please let us know how your investigations proceed. L De Groot,  MD.