Work Up of Thyroid Disorders
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Transcript of Work Up of Thyroid Disorders
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WORK UP OF THYROID
DISORDERS
Dr.Vijay Anand M S
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TESTS OF THYROID FUNCTION
No single test sufficient to assess thyroidfunction in all situations.
Results interpreted in context of clinicalcondition.
Serum TSH only test necessary in mostpatients with clinically apparent euthyroidnodules
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SERUM TSH
Normal 0.5-5.5 microunits/ml
Ultrasensitive chemiluminometric assay
Most sensitive & specific test for diagnosis for hyper andhypothyroidism and for optimizing T4 therapy
Reflects the ability of ant pituitary to detect free T4 levels
Inverse relationship between free T4 levels and log of TSHconcentration.
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TOTAL T4 & T3
T4 level 55-150 nmol/L
T3 level 1.5-3.5 nmol/L
RIA
Both free and bound forms
Total T4 reflect the output from thyroid gland
Total T3 in nonstimulated thyroid gland reflectsperipheral metabolism hence not suitable for screeningtest
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Total T4 levels increased not only in hyperT, butalso in those with elevated Tg levels sec. tocongenital, pregnancy, estrogen/progest use
Total T4 levels decreased in hypoT, decreased Tglevels such as anabolic steroid use,protein losingdisorders
Total T3 levels measured in clinically hyperthyroidpts with normal T4 levels
( T3 thyrotoxicosis )
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FREE T4 & T3
RIA
End organ resistance to T4 : REFETOFF syndrome T4 levels increased but TSH levels N
FT3 early hyperthyroidism
FT4 measured indirectly using T3 resin uptake
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TRH
Useful to evaluate pit TSH secretory function
500 mic of TRH iv measure TSH >30-50 min
N indiv TSH raise by 6 micIU/ml from baseline
Previously used to assess pts with borderlinehyperthyroidism
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THYROID ANTIBODIES
Anti Tg, AMA or Anti TPO, thyroid stimulatingimmunoglobulin TSI
Anti Tg, Anti TPO levels dont determine thyroidfunction,rather indicate underlying disorder, usuallyautoimmune thyroiditis
80% of Hashimoto-elevated Ab levels
Also increased in Graves, MNG, occasionallythyroid neoplasms
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SERUMTHYROGLOBULIN
Tg - only made by normal or abnormal thyroidtissue
Increases dramatically in destructive thyroid
processes-thyroiditis and overactive states such asGraves or toxic MNG
Most important usemonitoring patients with
differentiated thyroid cancers for recurrence,particularly after total thyroidectomy and RAIablation
Check for Anti Tg Ab
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SERUM CALCITONIN
0.4 pg/ml basal
Secreted by C cells
Function to lower serum calcium levels
Minimal physiologic effects in humans
Sensitive marker of Medullary thyroid cancer
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PLAIN FILMS
Not routinely ordered
May show:
Tracheal deviation
Pulmonary metastasis
Calcifications (suggests papillary or medullary)
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THYROID ULTRASOUND
Thyroid vs non-thyroid
Good screen for thyroid presence in children
Cystic vs. solid
Localization for FNA or injection
Serial exam of nodule size2-3 mm lower end of resolution
May distinguish solitary nodule from multinodular goitre
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THYROID ULTRASOUND
Findings suggestive of malignancy
* Presence of halo
* Irregular border
* Presence of cystic components
* Presence of calcifications
* Heterogeneous echo pattern
* Extrathyroidal extension
No findings are definitive
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NUCLEAR MEDICINE
Concept
Uses
Metabolic studiesImaging
Iodine is taken up by gland and organified
Technetium trapped but not organified
Usually only for papillary and follicular
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NUCLEAR MEDICINE
Radioisotopes:
I-131I-123
I-125
Tc-99m
Thallium-201
Gallium 67
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TECHNETIUM 99M
Most commonly used isotope (some authors)
99m: m refers to metastable nuclide
Decay product of Molybdenum-99
Administered as pertechnate (TcO4-)
Images can be obtained quickly
One-Stop evaluation
Hot nodules need f/u Iodine scan
Discordant nodules higher risk of malignancy
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IODINE
I 127 only stable isotope of iodine
I 123
Half-life 13.3 hr
Expensive, limited availabilityLow radiation radiation-exposure to patient
I 131
Half-life 8 days
Cheap, widely available
Better for mets (diagnostic and therapeutic) (high radiationexposure)
I 125 no longer used
Long half half-life (60 days); high radiation exposure with poorvisualization
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RADIOIODINE UPTAKE & SCAN
Radio labeled Iodine ( I-123) is given to thepatient which is actively trapped and concentratedby the thyroid gland.
It can assess:
Function Uptake
MorphologyScan
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RADIOIODINE UPTAKE
Uptake:
Measurements of % of the administered doselocalizing to the gland at a fixed time.
Reflects gland function.
Normal 24 hour uptake is ~10 to 30%.
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OTHER IMAGING MODALITIES
CT
Keep in mind iodine in contrast
MRI
PET
Not first line, but may be adjunctive
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FINE-NEEDLE ASPIRATION BIOPSY
Technique:
25-gauge needle
Multiple passesIdeally from periphery of lesion
Reaspirate after fluid drawn
Immediately smeared and fixed
Papanicolaou stain common
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