Endocrine Abstracts

In clinical practice, most thyroid disease is due to thyroid gland dysfunction and so can be detected by measurement of TSH alone. This is because the negative feedback of thyroid hormones on the hypothalamus and pituitary gland result in TSH levels that are closely, and inversely, correlated with circulating free thyroid hormone (FT₄, FT₃) levels. However, several conditions are exceptions to this rule and can be very hard to diagnose also due to a certain lack of awareness.

Examples of situations when measurement of TSH alone might be misleading include:

– interference in TSH and/or FT₄ measurements

– central hyperthyroidism due to TSH-secreting pituitary adenomas

– central hypothyroidism

– resistance to thyroid hormone action (RTHα or RTHβ)

– disorders and drugs interfering in thyroid hormone transport and metabolism

In addition, depending on the type of thyroid hormone being taken excessively by patients, exogenous thyrotoxicosis can present with variable abnormalities of thyroid function tests, making the diagnosis of such cases very challenging.