Metastatic Malignant Peritoneal Mesothelioma Mimicking an Autoinflammatory Syndrome in a 12-Year-Old Boy.

A case of a malignant peritoneal mesothelioma mimicking an autoinflammatory syndrome in a 12-year-old boy is reported. The patient initially presented with lymphadenopathy and weight loss but without abdominal pain. Three things confounded the initial diagnosis: a positive test result for a gene related to cryopyrin-associated periodic syndrome, a positive response to the autoinflammatory syndrome treatment, and a lymph node biopsy which showed "hyperplastic mesothelial cells in the lymph sinuses.