Changes of Thyroid Hormones and Their Binding Proteins during Plasma Exchange for Polyneuropathy in a Patient with Substituted Hypothyroidism due to Hashimoto's Thyroiditis.

Background: Pharmacodynamic studies and data concerning adaptation of thyroid substitution in patients with substituted hypothyroidism during plasma exchange (PE) is not available.

Case Report: We measured TSH, fT3 and fT4, total T4, thyroxin binding globulin (TBG), and albumin before and after 5 PE procedures in a 37-year-old women who underwent PE for a therapy-resistant polyneuropathy. Thyroxin was increased empirically by 8% resulting in a dose of 1.95 µg/kg per day.

Results: Despite larger reductions of total T4 and TBG over a series of 5 PEs (40-50% from baseline), only small reductions of 8% in fT3 and fT4 concentrations were documented with a concomittant increase in TSH level. Changes of fT4, fT3, and TSH remained within normal range.

Conclusions: i) Despite a significant decrease in total thyroid hormone pool following PE, fT4, fT3, and TSH concentrations changed only slightly. ii) Based on this observation, a general increase in thyroid replacement therapy before PE cannot be recommended, but considered in case of a high normal TSH level.