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A type of multiple endocrine neoplasia occurring as an isolated congenital presentation or as a distinct autosomal dominant disease. It is characterized by the 100% incidence of medullary thyroid carcinoma and frequent pheochromocytomas; patients seldom exhibit hyperparathyroidism. It is distinguished from MEN 2a by its characteristic physical appearance resulting from numerous neural defects including mucosal neuromas of the eyelids, lips, and tongue. The neural abnormalities also include widespread neurogangliomatosis of the gastrointestinal tract leading to abnormal gut motility. Treatment usually requires total thyroidectomy following evaluation for the presence of pheochromocytomas.