What about treating pandas with plasma exchange or immunoglobulin (ivig)?

No verdict. This is not a slam dunk decision. There may be something to it but the final word is not yet in. There is ongoing research in this area. The treatments you mention can be risky, especially for a child. Also in many cases symptoms of pandas improve spontaneously with the passage of time. For more information try this nih link: http://intramural.Nimh.Nih.Gov/pdn/web.Htm.
Sophisticated questn. Pediatric autoimmune neuropsychiatric disorders assoc. With strep. Infections occurs rapidly (@3-12 y/o) after a throat strep infection (similar to rheumatic fever/heart disease), causing obs-compulsive behavior, tic disorders, episodic periods of symptoms. Rx is geared toward the ocd/tics (ssri and/or behavioral rx). Pl xchng or ivig may or may not help (per studies). Get referral from the nimh.