Thyroid Stunning Revisited

TO THE EDITOR:

I read with interest the careful experimental study by Postgård et al. (1) and the accompanying editorial (2) in the Journal. This in vitro study suggested that thyroid stunning is a real phenomenon and is due to a decrease in iodide transport caused by the effects of radiation on thyroid cell iodine transport and not to cell death.

Although the investigators attempted to simulate the situation occurring in a thyroid cancer patient with residual functioning thyroid tissue who has been withdrawn from thyroid hormone replacement, there remain 2 issues:

First, in a patient who is to receive an imaging dose of ¹³¹I for cancer surveillance, functioning thyroid cells are exposed to a progressively rising thyroid-stimulating hormone level over a period of (typically) 10–14 d before administration of radiation. The investigators used a fixed pretreatment of 1 mU/mL in the experiment. Additionally, the protocol involved administration of methimazole, which would not occur in the patient setting.

Second, based on measurements of total DNA in the preparation, the authors concluded that stunning was due to decreased iodide transport and not to cell death from radiation. However, they used a nonproliferating cell culture model. Cells are most sensitive to radiation when they are dividing. This raises the possibility that the experiment may have been biased against finding cell death from radiation as a potential cause for stunning.