Change in mean syndrome symptom indexes with continuous administration of low-dose naltrexone (LDN) with dose escalation, monthly intravenous immunoglobulin (IVIg) starting 2 months later and a 2-week course of rifaximin. MCAS, mast cell activation syndrome; POTS, postural orthostatic tachycardia syndrome; SIBO, small intestinal bacterial overgrowth. Change in mean syndrome symptom indexes with continuous administration of low-dose naltrexone (LDN) with dose escalation, monthly intravenous immunoglobulin (IVIg) starting 2 months later and a 2-week course of rifaximin. MCAS, mast cell activation syndrome; POTS, postural orthostatic tachycardia syndrome; SIBO, small intestinal bacterial overgrowth. Leonard B Weinstock et al. BMJ Case Reports 2018;2018:bcr-2017-221405 ©2018 by BMJ Publishing Group Ltd