Sick Euthyroid Syndrome
  • Overview
    • Changes in thyroid hormone economy
      • (thyroid hormone economy refers to processes including thyroid hormonal synthesis, hormone transport in circulation, action and metabolism in peripheral tissues, and regulatory mechanisms)
    • Change caused by:
      • physical trauma
      • physiologic stress
      • severe illness
    • Sick euthyroid syndrome abnormalities:
      • altered transport
      • altered metabolism
      • altered TSH secretion regulation
      • altered thyroid function
    • Sick thyroid syndrome is associated with altered circulating thyroid hormone levels (both total & free)
  • Sick euthyroid syndrome (SES)-probably more common cause of thyroid hormone level abnormalities than intrinsic thyroid disease
  • SES classification:
    • Normal-T4 variant-
      • decreased T3 production secondary to decreased (inhibited) peripheral 5'- monodeiodination of T4.
      • Reduced serum T3 levels-reflecting disease severity
    • Low-T4 variant-
      • serum T4 levels reduced sufficiently to attain hypothyroid concentrations
        • secondary to significantly reduced T3 production rates and reduce serum total & free T3.
      • Typically associated with inappropriate TSH hyposecretion (unknown cause)
    • High-T4 variant-
      • Unusual (frequency = 1% of SES)
      • Most frequently observed in elderly women
    • Abnormal hormone binding in SES:
      • Associated with reduced T4 binding pre-albumin (transthyretin,TTR)
        • T4 & T3 are nearly entirely plasma protein-bound:
          1. thyroxine-binding globulin (TBG)
          2. T4-binding pre-albumin (transthyretin,TTR)
          3. albumin
  • SES Importance:
    • Changes in thyroid hormone will serum concentrations due to SES should not be interpreted in terms of intrinsic thyroid/pituitary dysfunction
    • Most patients with SES maintain normal levels of serum T4 & T3 -- normal-T4 variant of SES
    • Unknown whether SES is a beneficial or harmful response to illness
    • Patients with love T4 & T3 levels due to SES do not benefit from blurred hormonal treatment
Wartofsky, L., Diseases of the Thyroid, In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, pp 2012-2034