A Brief Synopsis of AFP's "Hypothyroidism: An Update"

A brief synopsis of: Hypothyroidism: An Update,DAVID Y. GAITONDE, MD; KEVIN D. ROWLEY, DO; and LORI B. SWEENEY, MD, Dwight D. Eisenhower Army Medical Center, Fort Gordon, Georgia

Am Fam Physician. 2012 Aug 1;86(3):244-251.

http://www.aafp.org/afp/2012/0801/p244.pdf

     Hypothyroidism is caused by either thyroid gland failure (primary) or poor stimulation of the thyroid gland from the pituitary gland or hypothalamus (secondary). Primary gland failure can be congential, autoimmune, or  iatrogenic. Common symptoms of hypothyroidism are weight gain, fatigue, depression, constipation, cold intolerance, dry skin, or hair loss. In children and infants, the most common signs are lethargy and failure to thrive. Menstrual irregularities and infertility are a common feature in women.  Cognitive decline may be the only symptom present in older adults.  Common signs are peripheral edema, brittle hair, goiter, pleural effusion, megacolon, and pericardial effusion. Patients may have ECG abnormalities including bradycardia and flat T waves. Lab findings may include hyponatremia, hypercapnia,  hypoxia, hyperprolactinemia,  hyperlipidemia, and elevated CK.
    Although universal screening is not recommended, patients who are symptomatic, or have risk factors,  including a history of autoimmune disease, previous radioactive iodine therapy, or a positive family history, should have a serum TSH drawn. If the TSH is elevated, then a T4 should be checked. A low T4 is seen in primary hypothyroidism and a normal T4 is seen in subclinical hypothyroidism.  A low TSH and low T4 signifies secondary hypothyroidism. Since the TSH level fluctuates, its best to check it in the morning.
     Most patients require lifelong levothyroxine (synthetic T4). The typical patient is started on 1.6 mcg/kg/day, given in the morning 30 minutes before breakfast. Certain patients need different dosages. Older patients with coronary heart disease are given 25-50 mcg/day, and increased by 25 mcg each 3-4 weeks until the optimal dose is found (a full dose could cause tachyarrhythmia and ischemia). Pregnant patients should get an extra 2 doses during the pregnancy.
     Patients with persistent symptoms should be checked for alternative causes, such as adrenal insufficiency,  depression, liver disease,  obstructive sleep apnea or chronic kidney disease. It can also be from deficiencies in B12, iron, or vitamin D. It is important to know that switching between name brand and generic medications for hypothyroidism is a bad idea because they have different bioavailabilities. myxedema coma is an extremely rare situation and should be treated in a ICU by an endocrinologist.