Mast Cell Activation Syndrome can show up in ways beyond the expected anaphylactic allergic reactions…since mast cells live in tissues, they can affect nearly every system of the body. MCAS may show up as IBS, migraines, atrial fibrillation, muscle/joint pain…the list is long. This long-overlooked condition is becoming more prominent and treatments are starting to emerge. Read about symptoms, diagnosis and treatments in this article.