A 38-year-old woman presents for a routine physical. Other than urgent care visits for 1 episode of influenza and 2 upper respiratory illnesses, she has not seen a physician for a physical in 5 years. She denies any significant medical history. She takes naproxen occasionally for chronic right knee pain. She does not use tobacco or alcohol. Recently, she has started using a meal replacement shake at lunchtime for weight management. She performs aerobic exercise 30 to 40 minutes per day, 5 days per week. Her family history is significant for type 2 diabetes mellitus, arthritis, heart disease, and hyperlipidemia on her mother’s side. She is single, is not currently sexually active, works as a pharmacy technician, and has no children. A high-risk human papillomavirus test was normal 4 years ago.
A review of systems is notable for a 20-pound weight gain over the past year, worsening heartburn over the past 2 weeks, and chronic knee pain, which is greater in the right knee than the left. She denies weakness, fatigue, nausea, diarrhea, constipation, or abdominal pain. Vital signs reveal a blood pressure of 146/88 mm Hg, a heart rate of 63 bpm, a temperature of 98°F (36.7°C), a respiratory rate of 16, a height of 5’7’’ (1.7 m), a weight of 217 lbs (98.4 kg), and a peripheral capillary oxygen saturation (SpO2) of 99% on room air. The physical exam reveals a body mass index (BMI) of 34, warm dry skin, and coarse brittle hair.
Lab results reveal a thyroid-stimulating hormone (TSH) level of 11.17 mIU/L (reference range, 0.45-4.5 mIU/L) and a free thyroxine (T4) of 0.58 ng/dL (reference range, 0.8-2.8 ng/dL). A basic metabolic panel and hemoglobin A1C level are normal.
What would you recommend?
In the United States, the prevalence of overt hypothyroidism (defined as a TSH level > 4.5 mIU/L and a low free T4) among people ≥ 12 years of age was estimated at 0.3% based on National Health and Nutrition Examination Survey (NHANES) data from 1999-2002.1 Subclinical hypothyroidism (TSH level > 4.5 mIU/L but < 10 mIU/L and a normal T4 level) is even more common, with an estimated prevalence of 3.4%.1 Hypothyroidism is more common in females and occurs more frequently in Caucasian Americans and Mexican Americans than in African Americans.1
The most common etiologies of hypothyroidism include autoimmune thyroiditis (eg, Hashimoto thyroiditis, atrophic autoimmune thyroiditis) and iatrogenic causes (eg, after radioactive iodine ablation or thyroidectomy) (TABLE 1).2-4
Initiating thyroid hormone replacement
Factors to consider when starting a patient on thyroid hormone replacement include age, weight, symptom severity, TSH level, goal TSH value, adverse effects from thyroid supplements, history of cardiac disease, and, for women of child-bearing age, the desire for pregnancy vs the use of contraceptives. Most adult patients < 50 years with overt hypothyroidism can begin a weight-based dose of levothyroxine: ~1.6 mcg/kg/d (based on ideal body weight).3
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