Trial of Naproxen Sodium for the Treatment of OCD in Children With PANDAS

Inclusion Criteria: 1. significantly interfering Obsessive-Compulsive Disorder (OCD) symptoms 2. ages 6- to 15-years-old 3. new-onset of OCD symptoms within the previous 18 months 4. sufficient fluency of English to understand study staff, procedures and questionnaires, 5. able to take medication in pill form 6. parent/legal guardian who can provide informed consent. Patients must also meet all criteria for PANDAS, which are: 1. prepubertal symptom onset 2. acute onset of symptoms (from no/minimal symptoms to maximum severity within 24-48 hours) and/or an episodic (relapsing-remitting) course 3. temporal association between symptomatic periods and infections with Group A Streptococcus (GAS) infection 4. presence of neurological abnormalities (e.g. handwriting deterioration, choreiform movements). The onset/exacerbation of OCD symptoms must also be accompanied by at least three of the following clinical signs and symptoms, including: 1. Markedly increased level of anxiety, particularly new onset of separation anxiety 2. Emotional lability, irritability, aggressive behavior and/or personality change 3. Sudden difficulties with concentration or learning 4. Developmental regression ("baby-talk", temper tantrums). 5. Sleep disorder (insomnia, night terrors, refusal to sleep alone) 6. Handwriting deterioration or other sign of motoric dysfunction (including new onset of motor hyperactivity, presence of choreiform finger movements, pronator drift or truncal instability) 7. Urinary frequency or increased urge to urinate; daytime or night-time secondary enuresis These co-occurring symptoms must be "severe" or "dramatic" and proceed from no/minimal symptoms to maximum severity within the same 24-48 hour interval during which the OCD symptoms arose. In addition to these inclusion criteria, PANDAS subjects will be required to provide documentation of a positive GAS infection via medical records. As the time between a documented GAS infection and the onset of PANDAS symptoms has not been defined in the PANDAS diagnostic criteria, the investigators will use a guideline of approximately six weeks or less between a documented GAS infection and the onset of OCD symptoms for inclusion into the study. Exclusion Criteria: 1. child who is acutely psychotic or suicidal 2. child has a serious neurological disorder or impairment (e.g. brain damage, blindness, deafness), an intellectual disability, or autism 3. history of immune modulating therapies for OCD/PANDAS symptoms 4. pre-existing liver, kidney, GI bleeding or clotting disorders (GFR \<75 mL/min/1.73m2) 5. history of ulcers in the digestive system 6. history of restricted fluid intake, as this could exacerbate side effects 7. concurrent antibiotic treatment or antibiotic treatment within one-week of baseline 8. pregnant or becomes pregnant 9. currently engaged in an intensive outpatient cognitive behavioral treatment program (more than weekly) 10. concurrent selective serotonin reuptake inhibitor (SSRI) or other psychoactive medication treatment except and unless the dose has been stable for at least 6 weeks (i.e. no recent titration, initiation, or change in dosage) 11. concurrent medications that do not meet the above criteria (e.g., other psychotropic medications or anti-inflammatory agents) 12. history of severe asthma or currently uncontrolled asthma