Bronchogenic carcinoma mimicking metastatic thyroid carcinoma

We present a case of a false-positive 131I scan in the follow-up of a patient with papillary thyroid carcinoma, which developed 24 yr after radiation therapy for Hodgkin's disease. In the primary evaluation of a neck mass, histology was typical for a papillary thyroid carcinoma and thyroglobulin staining was positive. After total thyroidectomy, 131I uptake was seen in the hilum and right lung. The initial interpretation of these foci as metastatic disease was not supported by the progressive clinical course despite radioiodine treatment. Hence, repeated bronchial brushings and cytology of the pleural effusion were obtained. These specimens were negative in thyroglobulin staining and positive for synoptophysin, a marker for small-cell bronchial carcinoma. Thereby a small to medium cell undifferentiated bronchial carcinoma was demonstrated, which apparently was actively taking up iodine. In conclusion, an atypical clinical course of a suspected metastatic thyroid carcinoma should lead to a reevaluation of the initial diagnosis to prevent an inappropriate therapeutic regimen.