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Diagnostic Tests – Hypothyroidism

by Carlo Raj, MD
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    00:01 Let’s diagnose hypothyroidism.

    00:03 Free T4 in all forms.

    00:07 TSH will be increased only in what kind of hypothyroidism? Primary.

    00:12 Anti-thyroglobulin or anti-thyroperoxidase are huge markers so that you can perhaps identify and diagnose a patient with Hashimoto.

    00:25 Hypothalamic and pituitary disease, tell me what these are respectively? You would call hypothalamic hypothyroidism - tertiary; you will call pituitary hypothyroidism - secondary.

    00:41 In both of these instances, you would expect your TSH levels to be decreased.

    00:46 Now, that first bullet point should make perfect sense that no matter what the cause of your hypothyroidism, by definition, you have free T4 in all forms.

    00:59 Hypothyroidism… synthetic thyroxine is treatment of choice, right? In other words, synthroid.

    01:06 Replacement dose typically, well, the dosage is here, you may take a look at it as you wish.

    01:12 Start a full dose in a young patient, however as it get older, you want to be careful as to how much synthroid that you give, please.

    01:23 Typically requires a dose increase when pregnant or taking oestrogen, why? If your patient presenting with hypothyroidism, you’re giving them thyroxine T4; patient pregnant oestrogen increased thyroid binding globulin, it is going to then rob or attach the free T4, therefore the administration of your synthroid that you’ve given initially is pretty much ineffective or has decreased effectiveness, doesn’t it? Increase your dosage, that you want to know.

    01:59 Adjust the T4 of replacement dose… well, here, once again, if you want to take a look at the dosage, you may do so in your own time; adjust those every six to eight weeks because you’re worried about… now, the half-life is important for you to know of approximately one week.

    02:16 You’re monitoring this patient just about as often as you can.

    02:21 Treatment, well, specific situations… subclinical hypothyroidism… controversial, we’ll let it go.

    02:28 Consider treating however if your patient has anti-thyroperoxidase given higher rate of progression to overt hypothyroidism.

    02:38 Overt meaning what? We’re going from subclinical into actual clinical so that becomes very important to you.

    02:46 The auto antibodies towards your peroxidase or perhaps your thyroglobulin.

    02:52 Huh, situation here… not good, myxoedema coma.

    02:59 You do everything in your power to slow this down.

    03:02 Look at the loading dose really high.

    03:04 Don’t worry about the dosage right now, it’s here for your reference.

    03:09 Stress dose glucocorticoid coverage often times that you find a patient with myxoedema coma is in a very, very highly stressful state.

    03:19 So, therefore, you were thinking about and very, very likely give him glucocorticoids.

    03:25 If no improvement at this point, you have no choice but to give this patient emergent IV T3.

    03:33 Hypothyroidism will make fever, tachy response to infection, lots of stress taking place; consider treating if positive for anti-thyroperoxidase given, once again, you’re worried about this patient go... given or going into overt hypothyroidism.

    03:51 Myxoedema coma is critical.

    03:54 This table here is going to give you a summary of all, I repeat, all real quick hyper and hypothyroid coverage.

    04:02 Primary hypothyroidism examples such as Graves’.

    04:05 We had a full discussion about radioactive iodine uptake previously.

    04:09 If you haven’t looked at it or if you are confused, this would be a good time to make sure that you’re perfectly clear about when you would have an increase or decrease with radioactive iodine uptake.

    04:20 If it’s primary increased free T4, decreased TSH; if it’s secondary hyperthyroidism an increase in TSH, increase in free T4, this would be a tumour that’s functioning in the anterior pituitary releasing too much TSH.

    04:33 Now, the topic at hand in this discussion is hypothyroidism.

    04:39 If it’s primary such as Hashimoto, you have a decrease in free T4, an increase in TSH.

    04:44 I wish to repeat here just one more time, this is where students keep missing is, is that in primary, not only do you have an increase in TSH, you also have an increase in TRH, thus you have hyperprolactinemia.

    04:56 Do not ever forget that.

    04:59 In secondary hypothyroidism, the problem is where? Anterior pituitary specifically.

    05:04 Anterior pituitary insufficiency is a topic that we have had in the very beginning of endocrinology where examples such as apoplexy and infarction and a non-functioning adenoma were all part… all differentials of pituitary insufficiency resulting in secondary hypothyroidism with decreased TSH and decreased free T4.


    About the Lecture

    The lecture Diagnostic Tests – Hypothyroidism by Carlo Raj, MD is from the course Thyroid Gland Disorders.


    Included Quiz Questions

    1. Tertiary hypothyroidism
    2. Hashimoto's thyroiditis
    3. Silent thyroiditis
    4. Cretinism
    5. Grave's disease
    1. Low TSH
    2. Low free T4
    3. Increased TSH
    4. Anti-TPO antibodies
    5. Anti-thyroglobulin antibodies
    1. Increased estrogen increases TBG, which lowers free T4
    2. Higher levels of T4 are required to cross the placenta
    3. Increased estrogen increases TBG, which increases free T4
    4. Systemic stress of pregnancy exacerbates hypothyroidism
    5. Pregnancy increases likelihood of sensitization to synthetic thyroxin
    1. Secondary hypothyroidism
    2. Hashimoto's thyroiditis
    3. Secondary hyperthyroidism
    4. Myxedema coma
    5. Grave's disease

    Author of lecture Diagnostic Tests – Hypothyroidism

     Carlo Raj, MD

    Carlo Raj, MD


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