When genetics disrupt the gut: Dysmotility and ganglioneuromatosis in multiple endocrine neoplasia type 2B syndrome

Abstract Multiple Endocrine Neoplasia type 2B (MEN2B) is a rare hereditary cancer syndrome characterized by medullary thyroid carcinoma, mucosal neuromas, and pheochromocytoma. Gastrointestinal involvement is common and often manifests as diffuse intestinal ganglioneuromatosis (IGN), which can impair motility and lead to severe constipation, pseudo‐obstruction, or megacolon. We report a male infant with known MEN2B who developed progressive abdominal distension and obstructive symptoms refractory to medical management. Initial rectal suction biopsies were unrevealing. Due to persistent symptoms, a diverting ileostomy was created for decompression, during which full‐thickness biopsies were obtained, ultimately establishing the definitive diagnosis of colonic ganglioneuromatosis. This case highlights the limitations of mucosal biopsies in detecting deeper neural pathology and underscores the importance of maintaining clinical suspicion for IGN in patients with MEN2B and persistent gastrointestinal symptoms despite a normal initial evaluation.