April 1980

Primary Hypothyroidism Misdiagnosed as Combined Hypothalamic Hypothyroidism and Secondary Adrenal Insufficiency

Author Affiliations

Adelaide, South Australia, Australia

Arch Intern Med. 1980;140(4):583. doi:10.1001/archinte.1980.00330160143056

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To the Editor.  —We spent some time trying to understand the pathophysiology of the patient claimed by Farese et al (Archives 139:99-100, 1979) as having a case of combined hypothalamic hypothyroidism and adrenal insufficiency and finally arrived at a simpler diagnosis. We think the following findings are relevant to the hypothalamic-pituitary-thyroidal axis: (1) biochemical hypothyroidism with decreased total thyroxine (T4) and decreased triiodothyronine resin uptake; (2) increased thyroid-stimulating hormone (TSH) level illustrating hypothalamic-pituitary response to hypothyroidism; (3) thyroidal response to exogenous TSH indicating submaximal stimulation by endogenous TSH; and (4) hyperreactive TSH response to thyrotropin-releasing factor (TRF) suggesting that the pituitary was responding appropriately for primary hypothyroidism. We interpret these findings as indicating primary hypothyroidism with impaired hypothalamic function because of decreased free T4 concentrations in the hypothalamus.1With regard to the hypothalamicpituitary-adrenal axis, the decreased basal serum cortisol concentration, lack of response to a single dose

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