Pathological features of multiple endocrine neoplasia type IIb in childhood.

The features of two patients with multiple endocrine neoplasia type IIb are described. Patient 1, a 9-year-old boy with marfanoid features, presented with chronic constipation and failure to thrive since infancy. Patient 2, a 12-year-old boy with marfanoid features, presented with a five-year history of persistent cervical lymphadenopathy. In patient 1, the myenteric and submucosal nerve plexuses at all levels of the small and large intestines were comprised of diffusely disorganized, hyperplastic, mature ganglion cells and nonmyelinated nerve fibers. Nerve plexus dissection with morphometric analysis showed marked thickening of the myenteric plexus with a quantitative increase in neural tissue. Patient 2 had a submucosal neuroma of the tongue. Both patients had occult medullary thyroid carcinoma, and patient 2 had cervical lymph node metastases. Both neoplasms showed positive staining for cytokeratin, carcinoembryonic antigen, calcitonin, bombesin, chromogranin, serotonin, and Leu 7. Electron microscopy showed membrane-bound, intermediate-sized, dense-core neurosecretory granules in tumor cells. In patient 2, calcitonin-positive amyloid was present with localization of calcitonin by immunoelectron microscopy to cytoplasmic secretory granules and to extracellular amyloid fibrils. These cases illustrate the potential for missed or delayed diagnosis in multiple endocrine neoplasia syndromes.