Cytologic changes simulating malignancy in thyrotoxic goiters treated with carbimazole.

The cytologic patterns in toxic goiters treated with carbimazole were studied. Most cases exhibited changes, especially the unusually large nuclei, that could be mistaken for malignancy in panoptic-stained material. Study of the nucleolar morphology by means of the toluidine blue stain, however, showed a clear difference from malignant nucleolar types, with the nucleoli displaying types as in the cells of benign euthyroid colloid goiters. No increased transcription activity was seen in the nuclei. Nucleolar staining is thus recommended to avoid diagnostic errors in these and similar atypical cases. The apparent cytostatic effect of carbimazole on thyroid cells is in accord with other reports in the literature.