X-linked hyper-IgM syndrome associated with poorly differentiated neuroendocrine tumor presenting as obstructive jaundice secondary to extensive adenopathy.

X-Linked Hyper IgM Syndrome (XHIGM) is a rare B-cell immunodeficiency disease. Patients with XHIGM are unable to switch immunoglobulin production from IgM to IgG, IgA, and IgE. Patients with XHIGM require periodic intravenous immune globulin to help prevent infections, and are also at risk for a variety of neoplasms. We describe a young man with XHIGM who presented with obstructive jaundice from malignant adenopathy from widespread, poorly differentiated neuroendocrine tumor. This has not previously been reported and represents a new association with XHIGM.