The Lab investigation of a patient shows lower limit of normal T4, & increased TSH. Which of the following is the most likely diagnosis-

Typically, in Hashimoto's thyroiditis, the pituitary gland in the brain will make more TSH (your blood test for TSH comes back high) because it thinks the thyroid is not making enough thyroid hormone. (Your T4 blood test may be below normal or on the low end of normal) . Ref - davidsons 23e p668