Cerebrospinal Fluid Thyroxine

Total and dialyzable thyroxine in cerebrospinal fluid and in serum were measured in 33 euthyroid patients with various neurological disorders and in 2 hypo-and 2 hyperthyroid patients. Total and dialyzable thyroxine in cerebrospinal fluid were found to be influenced by the protein concentration in cerebrospinal fluid and by the thyroid parameters in serum. Mean values for free thyroxine in the whole material were found to be almost identical in serum and in cerebrospinal fluid, suggesting a free passive passage of thyroxine through the blood-cerebrospinal fluid barrier. The total binding capacity of thyroxine was found to be higher in cerebrospinal fluid than in serum samples diluted to the same protein concentration as in cerebrospinal fluid, probably due to a higher concentration of prealbumin in cerebrospinal fluid.