Reduced tissue thyroid hormone levels in fatal illness

Area of Science:

• Endocrinology
• Metabolic Disorders
• Pathophysiology

Background:

• Severe nonthyroidal illnesses (NTIs) are often associated with altered thyroid hormone levels.
• Reduced serum triiodothyronine (T3) and thyroxine (T4) are common in NTIs, but tissue-specific changes are less understood.
• Distinguishing NTI-related hormone changes from primary hypothyroidism is clinically important.

Purpose of the Study:

• To investigate whether tissue concentrations of T3 and T4 are reduced in patients with severe NTIs.
• To compare thyroid hormone levels in various organs between NTI patients and healthy controls.
• To determine the organ-specific distribution of thyroid hormone deficiency in critical illness.

Main Methods:

• Autopsy tissue samples were analyzed from 12 patients who died from severe NTIs.
• Control group consisted of 10 individuals who died suddenly from trauma.
• Serum and tissue concentrations of T3, T4, free T4 index, and thyrotropin (TSH) were measured.

Main Results:

• NTI patients showed significantly lower serum T3 (79%), T4 (71%), and free T4 index (49%) compared to controls.
• Tissue T3 levels were reduced in cerebral cortex, hypothalamus, pituitary, liver, kidney, and lung (43-76%) in NTI patients.
• Tissue T4 levels were significantly lower in the liver (66%) but not significantly different in the cerebral cortex; heart and skeletal muscle T3/T4 did not differ significantly.

Conclusions:

• Severe NTIs lead to widespread deficiency of thyroid hormones in multiple tissues.
• The degree of thyroid hormone reduction varies significantly across different organs.
• These findings highlight the systemic impact of critical illness on thyroid hormone homeostasis.