HYPERPARATHYROIDISM ASSOCIATED WITH A CHRONIC HYPOTHYROID STATE

Reports of the coexistence of hyperparathyroidism and thyroid disease have raised the issue of a possible etiologic relationship. The presen t study tests the hypothesis that chronic elevation of thyroid-stimula ting hormone (TSH) is related to the development of hyperparathyroidis m. Four groups of 60 female rats were treated as follows: group 1, con trol; group 2, propylthiouracil (PTU) 0.0025%; group 3, PTU 0.0025% pl us thyroxine, 5 mu g two times per week; and group 4, only thyroxine. The animals' serum calcium, phosphorus, TSH, thyroxine, and parathyroi d hormone (PTH) levels were evaluated at 0, 6, 12, and 18 months. Sign ificant elevation of TSH was sustained throughout the 18 months in gro ups 2 and 3. The PTH levels were also significantly elevated in both g roup 2 and group 3 animals (P = 0.02), The histopathologic features of the parathyroids were evaluated at 18 months. In the group 2 (PTU onl y) animals, which had profound hypothyroid, 44% developed parathyroid adenomas. In the group 3 (PTU plus thyroxine) animals, who had mildly elevated TSH levels, 53% developed parathyroid adenomas. These finding s are consistent with the hypothesis that prolonged TSH stimulation ma y lead to hyperparathyroidism in the rat model.