ABIM Exam Disease of the Week Profile: Hashimoto’s Thyroiditis
Hypothyroidism is a commonly encountered condition in primary care clinic and thus, a high yield topic for the ABIM board examination. The featured ABIM Internal Medicine disease of the week will focus on the most common cause of hypothyroidism: Hashimoto’s thyroiditis.
PATHOPHYSIOLOGY/SYMPTOMS Hashimoto’s thyroiditis is an autoimmune disease in which the thyroid gland is attacked by antibodies. It is also known as chronic lymphocytic thyroiditis.
Although this condition can present with bouts of hyperthyroidism, hypothyroidism predominates the condition. Some of the most common presenting symptoms of Hashimoto’s thyroiditis are: – Weight gain or obesity – Memory impairment/loss – Fatigue – Constipation – Infertility – Hair loss – Cold intolerance – Depression – Bradycardia – Hoarseness or change in voice – Muscle weakness or atrophy – Joint pain – Menstrual irregularities – Abnormal elevation of liver function tests and cholesterol – Fibromyalgia
DIAGNOSIS Diagnosis of this condition is based on history, physical, and laboratory findings. With the above symptoms, hypothyroidism should be near the top of the differential diagnosis. On physical exam, the thyroid gland may be firm, lobulated, and large but can also be non-palpable. The best way to diagnose hypothyroidism is by checking free T4 levels and a TSH level. With primary hypothyroidism, the free T4 level will be decreased and the TSH level will be elevated. Additionally, if a patient has antibodies to thyroid peroxidase (anti-TPO) and/or antibodies to thyroglobulin, then Hashimoto’s thyroiditis is the likely diagnosis. These antibodies can cause progressive destruction of the follicles of the thyroid gland. Additionally, T lymphocytes can invade the thyroid gland.
MANAGEMENT Management of Hashimoto’s thyroiditis is thyroid replacement therapy (levothyroxine). Individuals who have underlying heart conditions should be started on a low dose of levothyroxine therapy. The usual starting dose in these individuals is 50 mcg of levothyroxine daily. Lower doses should be initiated in these patients because starting at a high dose can cause cardiac arrhythmias, especially atrial fibrillation, to occur. Levothyroxine should be taken with a full glass of water on an empty stomach. Food should not be consumed for at least 30-60 minutes after taking the medication. Certain medications that should not be taken concurrently are antacids, oral contraceptive pills, and multivitamins as these medications can inhibit the absorption of levothyroxine, and thus, not allow patient to achieve a euthyroid state. Euthyroid state simply means that the free T4 and TSH levels are in the normal range.
Individuals who do not have underlying cardiac disease can be initiated levothyroxine based on weight. The amount of levothyroxine that should be initiated in these patients is 1.6 mcg/kg. These patients should take the medication the same way as patients who have underlying cardiac conditions.
TSH and Free T4 levels should be checked initially every 6-8 weeks and if necessary, adjustments to the medication should be made. Before making adjustments on the dosage of medication, patients should be asked first if they are taking their medication properly. If they are taking their medication properly, then decisions need to be made on what to do with the dose of the medication. Suppose after 6-8 weeks the free T4 is still low and TSH is high, then the medication dose should be increased to the next higher dose of levothyroxine, since the patient has not achieved euthyroid state. If the free T4 is high and the TSH is low, this means that the patient is taking too much thyroid medication; therefore, the dose of the medication needs to be decreased. If the free T4 is normal but the TSH is high, this patient has subclinical hypothyroidism. Usually a higher dose of levothyroxine medication should be given in patients who have a TSH level of 10 mU/L or higher.
If patients are taking their medication properly and still are not achieving a euthyroid state, another possibility to consider is that the patient may have underlying celiac disease (gluten sensitive enteropathy), which is also an autoimmune disease. To determine whether an individual has celiac disease, antibodies to tissue transglutaminase need to be checked and an EGD procedure should be done. If the patient does have confirmed celiac disease, he or she will need to follow a gluten free diet. By adhering to a gluten free diet, it will usually allow for thyroid absorption, which will allow individuals to achieve euthyroid states, even at a lower dose.
COMPLICATIONS Some of the major complications of uncontrolled or undiagnosed Hashimoto’s thyroiditis include lymphoma, myxedema coma, and Hashimoto’s encephalopathy. Another common complication in children is growth retardation. Individuals who have growth retardation due to Hashimoto’s thyroiditis may require growth hormone if the growth has been stunted significantly.
CONCLUSION Understanding Hashimoto’s thyroiditis symptoms, diagnosis, management, and complications is high-yield for the ABIM board examination. Also, in clinical practice, internists who understand how to manage Hashimoto’s thyroiditis well will not have to refer a patient to an endocrinologist. This will lead to patient satisfaction as the patient will have to see fewer physicians and, thus, decrease the cost of office visits that are incurred by seeing several specialists.
You can review all the previous ABIM Exam disease of the week blog posts at the Knowmedge Blog. You can also find additional topics and questions directly from the Knowmedge Internal Medicine ABIM Board Exam Review Questions QVault.