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Hypothyroidism: Primary Versus Secondary

The causes of hypothyroidism are broadly classified as primary and secondary.

Primary hypothyroidism relates to defects/disease of the thyroid itself and are further delineated below. The most common cause is an autoimmune mechanism, where the body perceives healthy and normally functioning thyroidal tissue or products as foreign and attacks them.
  • Primary hypothyroidism– Related to the THYROID itself
    • Autoimmune interference with production
    • Insufficient supplies to make the hormones
    • Defective or blocked receptors
    • Faulty processing of hormone synthesis

Secondary hypothyroidism is attributed to an insufficient stimulation of the thyroid, most commonly due to lack of thyroid-stimulating hormone (TSH) production from the pituitary gland.
  • Secondary hypothyroidism– Related to the pituitary or hypothalamus; lack of stimulus
    • Insufficient TSH production from pituitary (COMMON)
    • Insufficient thyrotropin-releasing hormone (TRH) production from hypothalamus (rare)