Subclinical Hyperthyroidism

Euthyroid patient with TSH suppression
1. Low but detectable TSH: 0.1 to 0.4 mIU/L
2. Suppressed TSH: <0.1 mIU/L (greatest association with adverse effects, esp. >65 years old)

Prevalence in U.S. (study included patients over age 12 years old)
1. TSH <0.4 mIU/L: 3.2%
2. TSH <0.1 mIU/L: 0.7%
3. Hollowell (2002) J Clin Endocrinol Metab 87(2): 489-99 [PubMed]
More common in older adults
1. Prevalence in age over 70 years approaches 15% in Iodine deficient regions
2. Aghini (1999) J Clin Endocrinol Metab 84(2): 561-6 [PubMed]

Over-treatment of Hypothyroidism (excessive Thyroid Replacement)
1. Prevalence approaches 20%
Multinodular Goiter (esp. Iodine-deficient regions)
Graves Disease
Functional Thyroid Adenoma
Transient Thyroiditis
1. Silent Thyroiditis (TSH normalizes within months)
2. Subacute Thyroiditis
3. Postpartum Thyroiditis
Pituitary abnormalities (Free T4 also suppressed)
Early Hyperthyroidism in transition
Partially treated Hyperthyroidism
Iodine intake
1. Recent radiocontrast administration (e.g. IVP)
2. Amiodarone
3. Other excessive Iodine intake
Medications that suppress TSH
1. Corticosteroids
2. Dopamine
Other conditions
1. Sick Euthyroid Syndrome
2. Psychiatric illness (esp. affective disorders)

Significant Hyperthyroidism symptoms absent
Nonspecific symptoms may be present
1. Malaise
2. Tachycardia
3. Nervousness or anxiety
4. Muscle Weakness

Overt Hyperthyroidism
1. TSH 0.1 to 0.4 mIU/L: 1-3% risk per year (in age over 60 years)
  1. Rosario (2010) Clin Endocrinol 72(5): 685-8 [PubMed]
2. TSH <0.1 mIU/L: 27% 27% risk in 2 years (in age over 65 years)
  1. Rosario (2008) Clin Endocrinol 68(3): 491-2 [PubMed]
3. Cause of Subclinical Hyperthyroidism impacts risk of progression
  1. Multinodular Goiter is typically stable without progression
  2. Graves Disease is more unpredictable in terms of course
Cardiovascular effects
1. Atrial Fibrillation (Relative Risk: 3-5 in age > 60 years old)
  1. Auer (2001) Am Heart J 142(5):838-42 [PubMed]
  2. Sawin (1994) N Engl J Med 331(19): 1249-52 [PubMed]
2. Increased left ventricular mass
3. Decreased Heart Rate variability
Increased Mortality in older patients
1. Mortality increased by 20% over 10 years (especially if TSH persistently <0.1)
2. Haentjens (2008) Eur J Endocrinol 159(3): 329-41 [PubMed]
3. Sgarbi (2010) Eur J Endocrinol 162(3): 569-77 [PubMed]
Increased Osteoporosis risk in postmenopausal women
1. Rosario (2008) Arq Bras Endocrinol Metabol 52(9):1448-51 [PubMed]
2. Uzzan (1996) J Clin Endocrinol Metab 81(12): 4278-89 [PubMed]
Increased Muscle Weakness and atrophy risk

Indications (American Thyroid Association) for Subclinical Hyperthyroidism with TSH persistently <0.1 mIU/L
1. Age 65 years old or older OR
2. Age <65 years old with heart disease, Osteoporosis or Hyperthyroidism symptoms
3. Age <65 years old and postmenopausal and not on Estrogen or Bisphosphonates
4. Other indications
  1. May consider same management indications as above, for patients with TSH 0.1 to 0.4
Treatment options
1. Treat underlying cause of Subclinical Hyperthyroidism
2. Radioactive Iodine (Graves Disease, Toxic Multinodular Goiter, solitary autonomous Nodule)
3. Antithyroid Drugs