Brain tumor as a prototype of severe brain lesion in patients with "low T3 syndrome".

The purpose of our study was to contribute to better understanding of cerebrospinal fluid (CSF) as a valuable biological material in the research of brain tumors within the "low T3 syndrome", and to discuss the role of thyroid hormones in the central nervous system in subjects with severe cerebral lesions. We studied the levels of total triiodothyronine (tT3), total thyroxine (tT4), free triiodothyronine (fT3), free thyroxine (fT4), reverse triiodothyronine (rT3) and thyrotropin (TSH) in serum, and fT3, fT4, rT3 and TSH levels in CSF of patients with brain tumor, and compared the results with control group. Study results indicated a statistically significantly higher level of rT3 in serum and CSF of brain tumor patients vs. control group (p < 0.05). The rT3/fT3 ratio was highest in CSF and serum of brain tumor patients, yielding a statistically significant difference (p < 0.05). These results could suggest higher permeability of the blood-brain barrier in brain tumor patients. We also assume that rT3, in the framework of"cerebral low T3 syndrome", is also generated through local intracerebral conversion. Disruption of this process in severe cerebral lesion can lead to increased rT3 concentrations, i.e. development of the "low T3 syndrome".