OCCULT PAPILLARY THYROID-CARCINOMA IN HASHIMOTOS-THYROIDITIS PRESENTING AS A METASTATIC BONE-TUMOR

Some occult thyroid carcinomas are hypothesized to regress and be even tually obliterated. We report here a patient whose condition supports this hypothesis. A 51-year-old male with primary hypothyroidism due to Hashimoto's thyroiditis suffered from a rib bone tumor. He had a diff use goiter with no nodular lesion. Serum FT4 and TSH concentrations we re 0.8 ng/dl and 36.4 mu U/ml on taking 100 mu g/day of T4. Anti-Tg- a nd -TPO-Ab were strongly positive (99 and 1380 U/ml). The iodine 123 s cintigraphy demonstrated clear accumulation in the rib tumor, whereas the thyroid was scarcely visible. Biopsy of the rib tumor showed papil lary proliferation of large atypical cells, which were immunohistochem ically positive for thyroglobulin. Metastatic bone tumor of papillary thyroid carcinoma was therefore strongly suspected. He underwent a tot al thyroidectomy and the thyroid was stepwise sectioned completely at 3 mm intervals. The thyroid condition was diagnosed as Hashimoto's thy roiditis demonstrating diffuse and dense fibrosis, lymphocyte infiltra tion with lymphoid follicles and flattened atrophied follicles, but no carcinomatous foci were found. He was treated with I-131 and scintigr aphy after the ingestion showed distinct accumulation in the rib tumor s similar to that before thyroidectomy. No other abnormal uptake was o bserved. It is suggested that the primary occult thyroid papillary car cinoma regressed and was obliterated possibly by some immunologic or o ther host-resistance factors after it metastasized to the distant bone .