Parathyroid hyperplasia in multiple endocrine neoplasia type 1: a pathological and immunohistochemical reappraisal.

Twenty-nine parathyroid glands from nine patients with multiple endocrine neoplasia type 1 (MEN 1) syndrome were examined histopathologically and immunocytochemically to characterize better the nature of the accompanying parathyroid hyperplasia. The parathyroids showed varying degrees of nodular and diffuse (partial and total) hyperplastic involvement as well as apparently normal tissue. The nodules were usually multiple within any one gland and showed a varied cytoarchitectural 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. Apparently normal areas usually showed the strongest positive reaction. Amyloid material was observed within glandular lumens from hyperplastic areas in over half of the studied cases and stained positively for parathyroid hormone. This suggests that the hormone could be the precursor molecule of parathyroid amyloid as occurs with hormone-derived amyloid from other endocrine tumours. The overall findings indicate that the most striking feature of the parathyroid glands in MEN 1 is their variability, both morphological and functional, as indicated by their parathyroid hormone immunoreactivity.