Thyroid

Escape from Wolff-Chaikoff effect is presumed to be due to formation of inactive NIS dimers
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Though it is well known fact that initially FT4 is investigation of choice in the setting of antithyroid drug therapy for hyperthyroidism,when TSH recovers(≥ 3 months), it becomes the best method to follow on.
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How to calculate amount of daily iodine intake(DII) from urine iodine concentration?
-Median 24-hour urine volume is 0.9 ml/kg/hr
-24hr urine volume is 1.5 L
-Normal bioavailability of iodine is 92%
Hence DII= weight(kg) × 0.92×0.0009 L/kg/hr × 24 hr/day
Simplified,
DII=weight(kg) × 0.0234 × urine iodine(microgram/L)

For example, 100 µg/L urine iodine in a 50 kg man means DII of 117 µg.
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For diagnosing substernal extension of goiter investigation of choice is CT. 99mTcO4 doesnt help much as surrounding radioactivity of heart and great vessels is also high.Better to go for 123I scan.
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How to look for etiology of post-radioablative hypothyroidism,if previous records are not available,except for 99mTC04 scan showing diffuse uptake?
A:Clinically there are no residua of TAO/acropachy/pretibial myxedema.Anti-TSH-R abs even might not help as we know their titer decrease in accordance with decrease in thyroid volume.All this meaning ending up in presumptive diagnosis?
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Most common cause of acute thyroiditis is Staphylococcus aureus in adults and streptococcci in children,with mixed infections(anaerobes & gram negative bacteria) in almost 30%.My choice of antibiotics are vancomycin, piperacillin-tazobactam and metronidazole in combination.Corner stone management is hospital admission, parenteral antibiotics, I & D and not to forget to do barium swallow,CT/MRI to look for pyriform sinus (which is located normally just lateral to arytenoid cartilage) fistula.
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Growth of goiter during LT4 treatment for autoimmune thyroid disease indicates possibility of lymphoma and its should be FNAB
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Nodule with elevated TSH has 30% risk of carcinoma compared to a nodule with TSH in usual range.hence it is FNAB prior to LT4 suppressive therapy.
( K. Boelaert, J. Horacek, R. L. Holder, J. C. Watkinson, M. C. Sheppard, and J. A. Franklyn.Serum Thyrotropin Concentration as a Novel Predictor of Malignancy in Thyroid Nodules Investigated by Fine-Needle Aspiration.J. Clin. Endocrinol. Metab., Nov 2006; 91: 4295 - 4301.)
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One case ive encountered is 24 year-old-female with history of weight gain and found to have S.TSHof 3.2 µIU/ml with T4 of 4 ug/dl(N,5.5-11) who has been on LT4 150 µg/day.In such scenario ( total T4 is low and serum TSH is not elevated), TBG deficiency, central hypothyroidism, or euthyroid sick syndrome should be considered.Serum free T4 concentration is normal in TBG deficiency.
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Thyrotoxic Graves' disease with normal thyroidal 99m Tc pertechnetate uptake
Recently ive encountered one such case,a 26 year old goitrous male and not received antithyroid medications and having stare and upper eye lid retraction but no proptosis where biochemically and clinically patient was thyrotoxic and Tc scan was showing uptake in upper limit of normal (in contrast to low or no uptake in subacute/silent thyroiditis).Such things have been documented earlier(Annals of Nuclear Medicine,Vol 4,No2,43-48,1990) which interpret such cases are in initial phases of evolving thyrotoxicosis