Clinical thyroidology: beyond the 1970s' TSH-T4 Paradigm.

Area of Science:

• Endocrinology
• Thyroidology
• Clinical Medicine

Background:

• The 2012 American endocrine guidelines perpetuated the 1970s TSH-T4 Paradigm for hypothyroidism, defining it as hypothyroxinemia and relying on TSH and T4.
• This paradigm, despite acknowledged "pitfalls," discouraged consideration of patient symptoms and free T4/T3 levels, hindering individualized diagnosis and treatment.
• Decades of research have advanced understanding of thyroid hormone pathways, emphasizing the critical role of T3 effects for health.

Purpose of the Study:

• To critique the limitations of the current TSH-T4 Paradigm in hypothyroidism diagnosis and treatment.
• To advocate for a revised physiological definition of hypothyroidism based on tissue T3 effects.
• To highlight the importance of clinical symptoms and free T4/T3 levels over TSH for optimal patient management.

Main Methods:

• Critical analysis of existing hypothyroidism guidelines and the TSH-T4 Paradigm.
• Review of scientific advancements in thyroid hormone metabolism and signaling.
• Emphasis on clinical assessment (signs, symptoms) and serum free T4/T3 levels for diagnosis and treatment guidance.

Main Results:

• The TSH-T4 Paradigm has led to overdiagnosis, underdiagnosis, and inadequate treatment, causing patient dissatisfaction.
• TSH is an unreliable indicator of T3 status and can be misleading with standard T4 or T4/T3 therapy.
• Normalizing TSH or low FT4 with T4 alone often fails to achieve optimal T3 effect.

Conclusions:

• Hypothyroidism should be physiologically defined as insufficient tissue T3 effect, assessed via symptoms and FT4/FT3 levels.
• T4/T3 combination therapy, guided by clinical criteria, is more effective than T4 monotherapy.
• Informed clinical judgment, considering patient-specific factors, is essential for effective hypothyroidism management.