Hypothyroid: Primary and Seconday?

Discussion in 'Men's Health Forum' started by susmani, Jun 16, 2009.

  1. #1

    susmani Junior Member

    Could any one of you please explain the difference between primary hypothyroidism and secondary hypothyroidism. Thank you.
  2. #2

    marianco Doctor of Medicine

    Primary hypothyroidism means something is wrong with the thyroid gland itself, so that it is unable to produce thyroid hormone in sufficient quantities. For example, in Hashimoto's thyroiditis, the immmune system destroys the thyroid gland such that it cannot produce enough thyroid hormone no matter how high TSH goes.

    Secondary hypothyroidism means there are problems outside the thyroid gland which causes thyroid hormone levels to be insufficient. For example, if the brain is unable to produce enough TSH because the nervous system is not functioning well, then the thyroid gland is not signaled well enough to produce enough thyroid hormone for the body's needs. This is secondary hypothyroidism - often called central hypothyroidism (meaning the problem lies in the central nervous system). Secondary hypothyroidism may also occur if there is enough T4 being made but the body cannot convert it to the active form, t3. For example, in Alzheimer's disease, the brain is low in thyroid hormone (localized hypothyroidism) because the astrocytes of the brain cannot convert T4 to T3. The rest of the body may have enough thyroid hormone. But the brain does not (the brain is in a separate container from the rest of the body - being separated by the blood brain barrier). In secondary hypothyroidism, the problems with thyroid signaling are outside the thyroid gland.
  3. #3

    susmani Junior Member

    Thank you so much. Very well said.

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