VIP and Horner syndrome: In rare cases, patients with neuroblastoma develop Horner syndrome (disrupted sympathetic innervation on one side of the face with e.g. ptosis and miosis), or a paraneoplastic syndrome such as opsoclonus-myoclonus syndrome (development of neuroblastoma-related antineuronal antibodies with involuntary eye movements, muscle jerks, and ataxia) or a syndrome with watery diarrhea, hypokalemia and achlorhydria (WDHA syndrome) related to vasoactive intestinal peptide (VIP) secretion (5, 7-9).