Elevated free triiodothyronine: an uncommon form of hyperthyroidism

Area of Science:

• Endocrinology
• Thyroidology
• Internal Medicine

Background:

• Hyperthyroidism diagnosis traditionally relies on elevated serum thyroxine (T4) levels.
• Triiodothyronine (T3) elevations, particularly isolated ones, are recognized in specific thyroid conditions like nodular disease.
• The diagnostic spectrum of hyperthyroidism is generally understood to involve increased thyroid hormone levels.

Observation:

• This report details rare instances where hyperthyroidism was diagnosed despite normal or even low circulating T4 and T3 concentrations.
• The study highlights a diagnostic challenge where standard biochemical markers for hyperthyroidism are not met.
• Clinical presentation and other diagnostic modalities may be crucial in these atypical cases.

Findings:

• Hyperthyroidism can manifest biochemically with normal or low T4 and T3 levels, contrary to typical presentations.
• The findings suggest that reliance solely on T4 and T3 levels may lead to missed or delayed diagnoses in a subset of patients.
• Isolated T3 elevations in nodular thyroid disease represent a known variant, but normal/low levels are exceptionally rare.

Implications:

• Clinicians should consider hyperthyroidism even with non-elevated thyroid hormone levels, especially if clinical suspicion is high.
• Further research is warranted to understand the pathophysiology and diagnostic markers for this rare form of hyperthyroidism.
• Diagnostic algorithms for hyperthyroidism may need refinement to encompass these unusual biochemical presentations.