Subclinical Hypothyroidism

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Contents 1 Etiology 2 Epidemiology 3 Laboratory 4 Complications 5 Management 6 More General Terms 7 Additional Terms 8 References

Etiology

• auto- immune
• pharmaceutical agents

• lithium
• amiodarone or pharmaceuticals containing iodide

Epidemiology

• 11% of eldery, 3% of younger population [9]

Laboratory

• normal levels of serum T3 & serum T4
• increased levels of serum TSH

• values of 5-15 mU/L are characteristic

• anti-thyroid antibodies may herald a failing thyroid

• anti-thyroid peroxidase
• anti-thyroglobulin antibody

• lipid panel (elevated LDL cholesterol)

Complications

• possible increased risk of atherosclerosis & myocardial infarction [2]
• increased risk of adverse outcomes of pregnancy

• placental abruption ( RR = 3.0)
• preterm delivery ( RR = 1.8)
• respiratory distress
• admission to NICU

• increased risk of hip fracture in men ( HR=2.3), but not women [13]

Management

• patients are presumably mildly symptomatic & could benefit from treatment with thyroxine if

• serum TSH > 10 uU/ mL, or
• elevated LDL cholesterol, or
• positive anti-thyroid antibodies makes it likely disorder will progress to frank hypothyroidism

• benefits of treatment may include:

• improved cognition
• enhanced cardiac performance
• more favorable lipid profile
• reduced risk of cardiovascular events in patients < 70 years of age [8,13] (39% reduction) [13]

• no evidence to support treatment [4]

• USPSTF recommends against routine treatment [4]
• no evidence for treating elderly subjects with T4 to improve cognition [11]

• prognosis:

• may progress to overt hypothyroidism [4]

• 6%* with serum TSH of 5.0-9.0 mIU/L (52% normalize TSH) [5]
• 86%* with serum TSH of 15.0-19.9 mIU/L [5] * progression to overt hypothyroidism within 3.5 years

• no evidence that early treatment is of benefit [4]
• TSH generally normalizes within 5 years if TSH < 10 mIU/L [7]

More General Terms

• hypothyroidism

Additional Terms

• subclinical hyperthyroidism

References

1. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 15, American College of Physicians, Philadelphia 1998, 2006, 2009
2. Journal Watch 20(6):51, 2000 Hak AE et al Subclinical hypothyroidism is an independent risk factor for atherosclerosis and myocardial infarction in elderly women: the Rotterdam Study. Ann Intern Med 132:270, 2000 PMID: [1]
3. Solomon DH, in: UCLA Intensive Course in Geriatric Medicine & Board Review, Marina Del Ray, CA, Sept 12-15, 2001
4. Journal Watch 24(5):41, 2004 US Preventive Services Task Force (USPSTF), Ann Intern Med 140:125, 2004 [2] Helfand M, Ann Intern Med 140:128 <PubMed> PMID: [3] <Internet> [4]
   - Surks MI et al Subclinical thyroid disease: scientific review and guidelines for diagnosis and management. JAMA 291:228, 2004 PMID: [5]
5. Journal Watch 24(23):174-75, 2004 Diez JJ, Iglesias P. Spontaneous subclinical hypothyroidism in patients older than 55 years: an analysis of natural course and risk factors for the development of overt thyroid failure. J Clin Endocrinol Metab. 2004 Oct;89(10):4890-7. PMID: [6]
6. Prescriber's Letter 12(1): 2005 Subclinical Hypothyroidism: To Treat or Not to Treat Detail-Document#: [7] (subscription needed) [8]
7. Journal Watch 25(6):50, 2005 Casey BM, Dashe JS, Wells CE, McIntire DD, Byrd W, Leveno KJ, Cunningham FG. Subclinical hypothyroidism and pregnancy outcomes. Obstet Gynecol. 2005 Feb;105(2):239-45. PMID: [9]
8. Rodondi N et al, Subclinical hypothyroidism and the risk of heart failure, other cardiovascular events, and death Arch Intern Med 2005; 165:2460 PMID: [10]
   - Walsh JP et al, Subclinical thyroid function as a risk factor for cardiovascular disease Arch Intern Med 2005; 165:2467 PMID: [11]
   - Crapo LM Subclinical hypothyroidism and cardiovascular disease Arch Intern Med 2005; 165:2451 PMID: [12]
9. Surks MI & Hollowell JG Age-specific distribution of serum thyrotropin and antithyroid antibodies in the US population: Implications for the prevalence of subclinical hypothyroidism. J Clin Endocrinol Metab 2007, 92:4575 PMID: [13]
10. Lazar L et al Natural history of thyroid function tests over 5 years in a large pediatric cohort. J Clin Endocrinol Metab 2009 May; 94:1678 PMID: [14]
11. Parle J et al. A randomized controlled trial of the effect of thyroxine replacement on cognitive function in community-living elderly subjects with subclinical hypothyroidism: The Birmingham Elderly Thyroid Study. J Clin Endocrinol Metab 2010 Aug; 95:3623. PMID: [15]
12. Lee JS et al. Subclinical thyroid dysfunction and incident hip fracture in older adults. Arch Intern Med 2010 Nov 22; 170:1876 PMID: [16]
13. Razvi S et al. Levothyroxine treatment of subclinical hypothyroidism, fatal and nonfatal cardiovascular events, and mortality. Arch Intern Med 2012 Apr 23 <PubMed> PMID: [17] <Internet> [18]
14. National Guideline Clearinghouse Subclinical thyroid disease: scientific review and guidelines for diagnosis and management. ngc-guideline: [19]

subclinical hypothyroidism