Effect of Plasma Exchange in Thyroid Storm With Consideration of Its Distribution Into the Extravascular Space

Plasma exchange (PE), which directly removes some plasma thyroid hormones, is a treatment option for thyroid storm. However, the effect of PE has not been accurately assessed yet. Here we assessed the effect of PE in a patient with thyroid storm while taking into consideration the distribution of thyroid hormones in the extravascular space. A 51-year-old woman with thyroid storm underwent 2 PE procedures at our hospital. By measuring changes in thyroid hormone levels in plasma, fresh frozen plasma (FFP) used, and waste fluid during each 2.5-hour PE procedure, we calculated the efficiency of thyroid hormone removal based on the hypothesis that total thyroid hormone content before and after PE is the same. During the patient's first PE procedure, the estimated thyroxine (T₄) balance in the extravascular space (ΔX) was -70 μg, which corresponds to approximately 19% of T4 in the waste fluid. During the second PE procedure, ΔX was -131 μg, which corresponds to approximately 52% of T4 in the waste fluid. These data indicated that the source of removed T4 during PE varies. The amount of T₄ removed from the extravascular space should be taken into account during assessment of the effect of PE in thyroid storm.