Intravenous Immunoglobulin for PANDAS

Background: \- Some children experience a sudden onset of symptoms similar to those found in obsessive-compulsive disorder that may be caused by the body s reaction to an infection with streptococcal bacteria, most commonly seen as strep throat or scarlet fever. When the body s immune system reacts against brain cells following a streptococcal infection, the condition is known as PANDAS (pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections). The immune system response can be inactivated by treatment with a drug known as intravenous immunoglobulin (IVIG). Because there is insufficient research on IVIG s effects on the immune system of children with PANDAS, including whether IVIG is helpful in treating obsessive-compulsive symptoms related to PANDAS, researchers are interested in examining whether IVIG is an appropriate treatment for PANDAS and its associated symptoms. Objectives: \- To test the safety and effectiveness of intravenous immunoglobulin for the treatment of obsessive-compulsive disorder in children with PANDAS (pediatric autoimmune neuropsychiatric disorder associated with streptococcal infection). Eligibility: \- Children between 4 and 12 years of age who have obsessive-compulsive disorder (with or without a tic disorder) with sudden onset of symptoms following Group A streptococcal bacterial infections. Design: * Participants will be screened by telephone to obtain medical history and other information, followed by in-person screening at the National Institutes of Health Clinical Center. * Participants will be admitted to the hospital to receive 2 days of infusions of either IVIG or a placebo. Frequent blood samples, imaging studies, and other tests will be performed during this visit. * Six weeks after the inpatient stay, participants will return for further blood samples and other tests. Participants who did not receive the study drug, or who received the drug but did not respond to the initial IVIG infusion,