Definition: “Central hypothyroidism is defined as hypothyroidism due to insufficient stimulation by thyroid stimulating hormone (TSH) of an otherwise normal thyroid gland. It can be secondary hypothyroidism (pituitary) or tertiary hypothyroidism (hypothalamus) in origin.”
In centrally mediated hypothyroidism, such as hypothyroidism due to pituitary disease, TSH levels alone are unreliable for assessing the response to treatment with thyroid hormones. To monitor response to therapy requires measuring free T4 rather than TSH.
“Secondary centrally mediated hypothyroidism is caused by hypothalamic or pituitary disease in which TSH is not being produced, resulting in failure to stimulate the thyroid gland to make thyroid hormone. Standard treatment for this type of hypothyroidism is levothyroxine, but determining the response to therapy requires measuring free T4 rather than TSH.”
KTA: Central hypothyroidism is the only type of hypothyroidism in which TSH isn’t used for monitoring. T4 is used instead.
“Desiccated thyroid USP is a combination of T3 and T4 and response to treatment is usually assessed with TSH levels. T3 levels can fluctuate in patients treated with desiccated thyroid, as well as those who are on liothyronine (T3), and are therefore generally not used. TSH is also used to monitor treatment in patients with surgical hypothyroidism. Graves disease is an autoimmune disorder commonly causing hyperthyroidism, but patients usually become hypothyroid after treatment. TSH is used to monitor these patients as well.” ABFM
Further Reading / Reference
Gupta V, Lee M. Central hypothyroidism. Indian Journal of Endocrinology and Metabolism. 2011;15(Suppl2):S99-S106. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3169862/