Multiple Endocrine Neoplasia Type 1 Initially Presenting as Extensive Bone Metastases from Pancreatic Neuroendocrine Tumor: A Case Report

Abstract Multiple endocrine neoplasia type 1 (MEN1) is a hereditary tumor syndrome classically involving the parathyroid glands, pancreatic neuroendocrine tumors (pNETs), and pituitary adenomas. pNETs in MEN1 usually present with hormonal symptoms or liver metastasis, while bone metastasis as the dominant initial presentation is uncommon. We report a 30-year-old female who presented with progressive low back pain and bilateral lower limb numbness. Imaging revealed multiple osteolytic bone lesions and a small pancreatic tumor. Histopathological evaluation confirmed a well-differentiated neuroendocrine tumor of pancreatic origin with bone metastases. Further workup identified primary hyperparathyroidism due to an ectopic parathyroid gland and a nonfunctioning pituitary microadenoma, establishing a clinical diagnosis of MEN1. Notably, there was marked discordance in tumor grading between the primary pNET lesion (Ki-67: 2%) and the bone metastatic lesion (Ki-67: 20%). The patient was managed with a multidisciplinary approach, including palliative radiotherapy, medical treatment for hyperparathyroidism, and somatostatin analog therapy, resulting in symptomatic improvement and stable disease at follow-up. This case highlights an unusual presentation of MEN1 with pNET manifesting predominantly as bone metastases, and underscores the importance of evaluating tumor grade across different sites. Recognition of such atypical presentations may facilitate earlier diagnosis and guide appropriate management.