Subclinical Hyperthyroidism

Clinic A/P, adults, ENDOCRINOLOGY, Hospital A/P, Adults

Vignette: You have a patient with a TSH of 0.27 and normal T3 and T4 levels. How would you handle this patient?
-Dx: likely 2/2 central hypothyroidism, nonthyroidal illness, hyperthyroidism recovery, excessive ingestion biotin, etc
-Pt is asx at this point.
-Will f/u  closely because about 15% pts progress to overt hyperthyroidism in 2yrs. Also, there is an increased risk of CAD, AF, Osteoporosis.
-Will recheck labs in 3-6 mo to document resolution vs. persistent. If persistent and TSH < 0.1, will consider treatment and RAIU.
-If TSH between 0.1-0.5, we will consider treatment when elderly, symptomatic, or with CV disease.
-Definition: Subclinical Hyperthyroidism = normal T4 & T3 concentrations in the presence of low TSH
-Most common causes of subclinical hyperthyroidism are treatment with T4 (exogenous) and autonomously functioning thyroid adenomas and multinodular goiters (endogenous).

Will get the following labs/studies:

  • Serum TSH (initial)
  • Repeat TSH and do free T4, T3 serum levels if initial TSH <0.5 to establish a diagnosis.
  • Monitor: repeat TSH, T4, T3 in 1-3 months
  • Radioactive iodine uptake
  • Thyroid US to r/o nodules.
  • Thyrotropin receptor antibodies (TRAb) or TSI confirms Graves
  • Will any underlying condition as in overt hyperthyroidism
  • Will evaluate and f/u for possible complications such as atrial fibrillation (older adults), decreases bone mineral density (post-menopausal women)

 

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Subclinical hyperthyroidism is defined as normal serum free thyroxine (T4) and triiodothyronine (T3) in the setting of a subnormal Thyroid-Stimulating Hormone (<0.5 mU/L). Patients taking thyroid hormone replacement are at risk of developing subclinical hyperthyroidism, and up to 25% of patients on levothyroxine develop low serum TSH. Among other causes of endogenous subclinical hyperthyroidism, the most common are thyroid adenomas, multinodular goiters, and thyroiditis.

Ddx: Central hypothyroid, Nonthyroidal illness, Recovery from hyperthyroidism, Excessive biotin intake (artifactually low TSH), Shifting in TSH distribution in healthy patients (African descendants).

https://www.uptodate.com/contents/subclinical-hyperthyroidism-in-nonpregnant-adults?source=search_result&search=subclinical+hyperthyroidism&selectedTitle=1%7E46

http://www.aafp.org/afp/2011/0415/p933.html

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