Endocrine Abstracts

We studied levels of T₃, T_4, FT₃, FT₄, rT₃ and TSH concentrations in serum and FT₃, FT₄, rT₃ and TSH concentrations in cerebrospinal fluid (CSF) in 10 patients with brain tumor and 20 patients with acute stroke and compared them to 7 patients in control group (further clinical evaluation in control group did not show brain lesions). All patients were euthyroid. The study was approved by local Ethical Committee. Serum T₃ and T₄ levels were similar in all three group. The values of FT₃, FT₄ and TSH did not significantly differ to control group neither in serum nor in CSF. On the contrary, significantly elevated rT₃ was found in serum and CSF, at both group of patients. The rT₃/FT₃ ratio were the highest in patients suffering from brain tumor and were significantly elevated compared to control group (serum, CSF), as well as compared to the patients with acute stroke. The values were particularly high in CSF (4 times higher) which would suggest that changes connected with “low T₃ syndrome” in patients with brain lesion are more obvious in CSF than in serum and identify brain tumor as a prototype of serious “local” nonthyroid illness. Serum and CSF test showed positive correlation for FT₄ and FT₃ in patients with acute stroke and for rT₃ in patients with brain tumor. This suggests that hormones are passing through still functional blood-brain barrier. The study did not show correlation between elevated rT₃ or rT₃/FT₃ ratio and poor prognosis. Thyroid hormones are present in CSF at concentration lower than in serum. There are probably two mechanisms responsible: hormones are partly crossing the blood-brain barrier from serum, but also T₃ and rT₃ may derive from local conversion of T₄ within the central nervous system. The impairment of this conversion which occurs in different brain lesions could be responsible for the changes in hormones level known as “low T₃ syndrome”, which are particularly evident in CSF.