work up of thyroid disorders

8/3/2019 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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