Hypothalamic-pituitary axis dysfunction in critically ill patients with a low free thyroxine index

Area of Science:

• Endocrinology
• Critical Care Medicine
• Neuroendocrinology

Background:

• Critically ill patients often exhibit endocrine dysfunction.
• The hypothalamic-pituitary axis (HPA) and its interaction with thyroid hormones are crucial in critical illness.

Purpose of the Study:

• To investigate the association between hypothalamic-pituitary axis abnormalities and free thyroxine index (FTI) in critically ill patients.
• To compare pituitary hormone responses in critically ill patients with normal and low FTI.

Main Methods:

• Anterior pituitary gland testing using corticotropin-releasing hormone (CRF), growth hormone-releasing hormone (GHRH), thyrotropin-releasing hormone (TRH), and gonadotropin-releasing hormone (GnRH).
• Serial hormone measurements (baseline, response amplitude, time to maximal response, velocities, integrated responses) in 14 critically ill patients and 20 healthy volunteers.
• Patients were categorized into healthy, sick with normal FTI, and sick with low FTI groups.

Main Results:

• Critically ill patients (Groups II and III) showed elevated urinary and serum cortisol and serum prolactin (PRL).
• Group III (sick/low FTI) had lower baseline ACTH, slower ACTH and TSH response velocities, and decreased PRL integrated responses compared to Group II (sick/normal FTI).
• Cortisol response parameters and gonadotropin/growth hormone responses were similar across groups.

Conclusions:

• Critically ill patients exhibit hyperprolactinemia and HPA axis activation.
• A low FTI in critical illness is associated with attenuated PRL, TSH, and ACTH responses, despite preserved adrenal cortisol output.
• These findings highlight specific neuroendocrine adaptations in critically ill patients with hypothyroidism.