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Home > CME > Courses
The Diagnostic Approach to a Low Thyroid Stimulating Hormone, Part I

Presented by the University of Alabama School of Medicine
Division of Continuing Medical Education

Release Date: April 6, 2011
Expiration Date: April 6, 2014

Target Audience
Objectives
Source
CME Participation
Accreditation & Credit

Introduction
Case 1
Case Question #1
References and Resources

TARGET AUDIENCE:
Primary care physicians

OBJECTIVES:
Upon completion of this CME activity, participants should be able to:
  • Identify appropriate strategies for diagnosing hyperthyroidism
  • Describe appropriate management strategies for patients with hyperthyroidism
  • Recognize the variety of available tests for approaching an abnormal TSH
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SOURCE:
FACULTY:

AUTHORS:

Thomas G. Kincer, MD
Clinical Professor of Medicine

Mohammad Irfan, MD

Zhenhong Zhou, MD

Willie Jones, MD

Bethany Meredith, DO

Montgomery Family Medicine Residency Program
Montgomery, Alabama

CO-EDITOR:

Michael Schoen, PhD
Division of Continuing Medical Education
University of Alabama School of Medicine, UAB
Birmingham, Alabama

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DISCLOSURE:
The authors and editor have no commercial affiliations to disclose.

Because of the nature of preliminary studies, some products mentioned are unlabeled and investigational. Dosages, indications, and methods of use of drugs mentioned in this publication may reflect the experience of the authors, clinical literature, or other resources. Therefore, please see the full prescribing information before using any licensed product mentioned.

CME PARTICIPATION:
To participate in this online course for CME credit, please review the objectives before beginning the program. Complete the course and the self-assessment test before April 6, 2014 to receive CME credit. Your certificate will then be available online. This process should take approximately 1 hour.
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ACCREDITATION:

The University of Alabama School of Medicine is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The University of Alabama School of Medicine designates this enduring material for a maximum of 1 AMA PRA Category 1 Credit™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

The boards of nursing in many states, including Alabama, recognize Category 1 continuing medical education courses as acceptable activities for the renewal of license to practice nursing.

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DISCLAIMER:
Dosages, indications, and methods of use of any drug referred to in this publication may reflect the clinical experience of the authors, clinical literature, or other clinical resources. Therefore, please see the full prescribing information before using any product mentioned. UAB is an equal opportunity/affirmative action institution.
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INTRODUCTION:

Unraveling thyroid disorders can be confusing because of the negative feedback loop and the numerous thyroid dysfunctions. The problem is compounded by the diverse presentation of thyroid disorders in educational materials. Thyroid abnormalities can be presented according to their causes such as hypothyroidism, hyperthyroidism, thyroiditis, nodules, goiters, cancers and causes of abnormal laboratory values. Since physicians are often confronted with abnormal laboratory values, this article will highlight the diagnostic approach to a low TSH.

A quick review of the negative feedback loop reminds us that TRH is released from the hypothalamus which in turn causes the release of TSH from the anterior pituitary. TSH then binds to the TSH receptor on the thyroid gland causing secretion of T4 and to a lesser degree, T3. T4 is converted to the active form, T3, in the periphery and also acts to suppress the release of TRH and TSH thus decreasing the secretion of more T4.[1] Minor elevations in T4 can maximally suppress the release of TSH.[2] A low TSH is either due to the pituitary’s inability to produce TSH or from excess T4 or T3 suppressing production.

Excessive levels of thyroid hormone is due to all forms of hyperthyroidism, thyroid replacement medications and, rarely, exogenous thyroid hormone producing tumors, known as Struma ovarii. The most common causes of hyperthyroidism include Grave’s Disease, Toxic Multinodular Goiter, Toxic Adenoma, and Subacute Thyroiditis, also known as DeQuervain’s Thyroiditis. In these cases, the TSH would be undetectable and the T4 or T3 levels elevated.

Although uncommon, one must consider the inability of the pituitary to produce TSH as a cause of low TSH. An undetectable TSH along with low levels of T4 and T3 readily identifies this condition. Causes include pituitary tumors, infiltrative diseases such as sarcoidosis, brain injury, rapid blood loss known as Sheehan’s syndrome and infections.[3]

The clinician should use the TSH as the screening test for symptoms of thyroid dysfunction. TSH suppression or elevation is ultrasensitive to even minor changes in circulating T4 or T3. A normal TSH level indicates an intact hypothalamic-pituitary-thyroid axis. A normal TSH does not exclude the possibility of nodules, goiters and tumors. If the clinician obtains an abnormally low TSH, the next step is to obtain a free T4 and free T3. This will allow the clinician to distinguish between a thyroid and a pituitary disorder.

Radioactive Iodine Uptake, RAIU, testing will show excess uptake of iodine in the autonomously hyperfunctioning thyroid gland as in Grave’s disease, toxic multinodular goiter or toxic adenoma. In contrast, the RAIU will show little to no uptake in the hypofunctioning thyroid gland as in DeQuervain’s thyroiditis, thyroid replacement hormone usage or Struma ovarii[4]. Pain in the anterior neck, tenderness to palpation of the thyroid, a low TSH and high free T4 is often all that is needed to diagnose DeQuervain’s thyroiditis[5]. Additionally, in thyroiditis the serum thyroglobulin will be high (see table 1). In contrast, patients taking excessive thyroid hormone will have a low TSH, high free T4, low RAIU and a low serum thyroglobulin.

It is unlikely that the clinician will be able to read one article and have a comprehensive understanding of the pathophysiology and clinical approach to the management of thyroid disorders. Even the most advanced clinician may need to periodically review topics in thyroid disease and consult texts, articles and specialists if the patient’s presentation is not straight forward. This module, along with Part II, will present a variety of patient cases designed to illustrate common symptom presentations and management strategies.

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Case 1:

A 36 year old female new to town wants to get established at your office. She has a history of hypertension and a C-section 4 months ago. The patient exercises four hours daily and mentions that she is trying to get to her pre-pregnancy weight. Her only medication is lisinopril. Today she is complaining of nervousness, fatigue, insomnia and dysmenorrhea. The patient is 5’6” tall and weighs 125 pounds. Her oral temperature is 99°F, BP 125/80, Pulse 112 and respirations 22. On physical examination the patient appears anxious with a mild symmetrical tremor in her hands. You consider hyperthyroidism in the differential diagnosis.

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Case 1 of 2, Question 1 of 7

1. Which laboratory test is the most appropriate first step in diagnosing hyperthyroidism?

A. Thyroid Releasing Hormone
B. ACTH
C. TSH

D. Free T4
E. Reverse T3


 

 
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