Parathyroid hyperplasia in tertiary hyperparathyroidism: a pathological and immunohistochemical reappraisal

Thirty‐one parathyroid glands from 11 patients with tertiary hyperparathyroidism were examined histologically and immunohistochemically to characterize better the nature of the accompanying parathyroid hyperplasia. The parathyroids showed varying degrees of nodular and diffuse hyperplastic involvement as well as apparently normal background tissue. The nodules were usually multiple within any one gland and, together with diffuse hyperplastic tissue, showed a varied cyto‐architectural pattern. All glands studied showed both cellular argyrophilia and parathyroid hormone immunoreactivity. The staining pattern for parathyroid hormone ranged from negative or weak to strong, and from patchy to diffuse in hyperplastic tissue from different glands and within the same gland, regardless of the cell type. Apparently normal areas usually showed only patchy weak to moderately strong parathyroid hormone positivity. From the data obtained the most striking feature of the parathyroid glands in tertiary hyperparathyroidism is their extreme variability, both morphological and functional, as indicated by parathyroid hormone immunoreactivity. Furthermore, the generally lesser degree of parathyroid hormone immunoreaction observed in apparently normal parathyroid tissue may reflect suppression of hormone synthesis, with accompanying morphological regression to normal of pre‐existent diffuse hyperplasia by autonomous hyperfunctioning nodules associated with tertiary hyperparathyroidism.