Management of Subclinical Hypothyroidism

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Introduction

Dr. Joey Tabula  01:22 Good day, dearest doctors. I am Dr. Joey Tabula, Senior Medical Manager here at Merck. We are pleased to welcome you to today's webinar, where we will discuss subclinical hypothyroidism. Just a few reminders before we begin tonight's learning session, this activity is strictly for healthcare professionals, and it will be followed by the Q&A session in the latter part. You may type in your questions in the comment box at any time during the presentations.

Dr. Joey Tabula  01:59 Tonight, we are talking about the importance of early screening, diagnosis, and treatment of subclinical hypothyroidism. This expert lecture will help us learn more about the proper clinical management of this disease using the latest guideline recommendations and updates.

Dr. Joey Tabula  02:23 Our speaker for tonight is a Consultant of Endocrinology and presently heads the Thyroid Advocacy Council of the PSEDM and is in charge of the upcoming national celebration of the Goiter Awareness Week later this January. He's also a past Board of Directors of the Philippine Thyroid Association. Presently he practices in San Jose Del Monte Bulacan and Quezon City. To talk about subclinical hypothyroidism management, dear doctors, let's give a warm welcome to Dr. Nestor Eric Laplano.

Objectives: Management of Subclinical Hypothyroidism (SCH) Treatment

Dr. Nestor Eric Laplano  03:07 Thank you. Good evening, Dr. Joey Tabula, and thank you again for that very kind introduction. Good evening everyone, and Happy New Year. It is my honor and pleasure to be invited to talk about subclinical hypothyroidism. I would like to thank everyone for sharing your time and effort to watch this particular webinar, and at the end, I would like to wish everyone that you will learn a lot from managing this particular condition.

Dr. Nestor Eric Laplano  03:34 We saw that because of the pandemic; even our patients have become well-versed with the term asymptomatic. And so, for tonight, we're going to look at a thyroid condition that is usually asymptomatic but nevertheless very relevant and important and may even be more prevalent than primary hypothyroidism.

Dr. Nestor Eric Laplano  03:57 These are my disclosures, and for the next few minutes, we will just review whom you should test for possible thyroid dysfunction, and who will benefit from treating subclinical hypothyroidism, and of course, just a few clinical pearls in thyroid hormone replacement.

Thyroid Hormone Regulation

Dr. Nestor Eric Laplano  04:17 To better understand subclinical hypothyroidism, we'll just breeze through the basics of thyroidology. So we all know that thyroid hormone synthesis is largely regulated by an intact hypothalamic-pituitary-thyroid or the HPT axis via the TRH coming from the hypothalamus and the thyrotropin or the TSH (thyroid-stimulating hormone) coming from the pituitary. These two would stimulate your thyroid to produce your thyroid hormones which we call T4 and T3. Much of the T4 to T3 conversion occurs in the kidneys, in the muscles of the heart, and in the skeletal muscles in the pituitary, and the entire axis is governed by a negative feedback mechanism such that overproduction of your thyroid hormones by the thyroid will inhibit this particular HPT axis.

Dr. Nestor Eric Laplano  05:16 So TSH on your Y-axis and the T4 of the thyroid hormone on your X-axis exist in a log-linear relationship such that small, incremental changes in your T4 would result in large incremental changes in the TSH in the opposite direction. TSH secretion is exquisitely sensitive to plasma concentrations of your free thyroid hormones, providing an inherently indirect but precise and accurate barometer of thyroid hormone status, making it the single best screening test for thyroid hormone dysfunction in an impact hypothalamic-pituitary and thyroid axis.

HPT Axis Negative Feedback

Euthyroid state

Dr. Nestor Eric Laplano  06:06 So, this negative feedback mechanism and the log-linear relationship between your TSH and thyroid hormones may be further illustrated by imagining them on either side of a seesaw. Now, with the fulcrum of the center more proximal towards the side of your T4 and T3. If you have a normal T4 and T3 and normal TSH, we call that a Euthyroid state.

Subclinical hypothyroidism

Dr. Nestor Eric Laplano  06:34 A minuscule drop in your thyroid hormone production would resort to a large incremental increase in your TSH, and this condition is termed as your subclinical hypothyroidism. So please remember that subclinical hypothyroidism is characterized by an abnormal, elevated TSH in the presence of normal T4 and T3. I see a lot of patients being referred to me with subclinical hypothyroidism symptoms, but the referral patient has normal TSH and abnormal T4 and T3. So remember, subclinical hypothyroidism is characterized again by an abnormally elevated TSH in the presence of your normal T4 and T3.

Primary/overt hypothyroidism

Dr. Nestor Eric Laplano  07:24 Consequently, your thyroid hormone levels will fall below normal levels with subsequent very high levels of your TSH, and this is what we call your primary/overt hypothyroidism. Later on in the treatment of subclinical hypothyroidism, we will highlight some differences in the treatment for your subclinical hypothyroidism and primary/overt hypothyroidism.

Dr. Nestor Eric Laplano  07:53 On the other side of the spectrum, we can see that a suppressed or a very low TSH can result from minor elevations of your T4 and T3, which we call your subclinical hyperthyroidism.

Dr. Nestor Eric Laplano  08:10 Eventually, the thyroid hormones will become very high, such that you will have almost imperceptible or undetectable TSH levels. So, you will see in the laboratory result TSH less than 0.0001. So almost undetectable or imperceptible.

Subclinical Hypothyroidism Treatment Guidelines 2021

Dr. Nestor Eric Laplano  08:29 Subclinical hypothyroidism becomes more prevalent as one age because, for every decade beyond 30 years old, your TSH increases by 0.3 mU/I, and that increase is more evident in females. So the majority of our patients with subclinical hypothyroidism would be females, although it doesn't mean that males will not have subclinical hypothyroidism, and the majority of them will have a mildly elevated TSH.

Dr. Nestor Eric Laplano  09:08 Locally, we have a prevalence of 2.18%, as was studied by endocrinologists a decade ago, and that means that two in 100 adult individuals may have subclinical hypothyroidism. And you can see here that it's actually more prevalent in patients with overt/primary hypothyroidism.

Who is at risk for SCH?

Dr. Nestor Eric Laplano  09:32 So who should get tested, or who among your asymptomatic patients should get tested for possible subclinical hypothyroidism? Of course, as mentioned earlier, 

• Females, especially those who are more than 60 years old
• Persons with the autoimmune disease–this is very famous now in terms of getting vaccine clearance: those who have autoimmune diseases, those who have type 1 diabetes, pernicious anemia, or rheumatoid arthritis.
• Those who have prior hyperthyroidism. Because in the natural course of some hyperthyroidism, they will eventually become hypothyroid, and initially, they will exhibit subclinical hypothyroidism. 
• Patients with a history of head and neck radiation: those who have cancers, those who have hyperthyroidism treated with radioactive iodine or those with nodules suppressed with radioactive iodine therapy, and 
• Those on lithium and amiodarone.

AACE 2012 hypothyroidism guidelines

Dr. Nestor Eric Laplano  10:42 Of course, the AACE or the American Association of Clinical Endocrinologists gave us a hint of those conditions, who will be warranted check or be checked for thyroid hormone dysfunction, especially in the presence of adequate treatment. And yet, they still exhibit the following conditions:

• hypercholesterolemia, dyslipidemia, despite maximum statin therapy, 
• those with uncontrolled hypertension on multiple therapies, 
• those who have malaise and fatigue, 
• those with arrhythmias, 
• those who have unexplained weight gain or undeniably gaining weight, despite saying that they are not eating a lot this pandemic, 
• those who have anemia, 
• cardiac dysrhythmias 
• GI manifestations, and 
• Alopecia.

Dr. Nestor Eric Laplano  11:40 We must remember that your serum TSH can be transiently elevated. Your TSH at one point will not be able to reflect the TSH for the whole day. And therefore, in the diagnosis of subclinical hypothyroidism, it is important to repeat first your TSH after one to three months before deciding to treat your patients for subclinical hypothyroidism.

Dr. Nestor Eric Laplano  12:07 As mentioned, normalization of TSH is more likely in patients with negative antithyroid antibodies and or anti-TPO antibodies and in those patients with a TSH of less than 10. So in your patients with subclinical hypothyroidism, the decision to treat it may also be prudent to also check for your anti-TPO antibody and also for prognostication if they will eventually develop into overt hypothyroidism.

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