Parallels between Sydenham chorea (SC), the neurologic manifestation of rheumatic fever, and childhoodonset OCD suggest that the two disorders may have a shared etiopathogeneis. 1 The disorders have similar regional localization—both OCD and SC have evidence of basal ganglia dysfunction, particularly in the caudate nucleus, which is thought to disrupt signals traveling along the orbitofrontal-striatal pathways. Further, over 70% of children with SC report that they have experienced an abrupt onset of repetitive, unwanted thoughts and behaviors 2–4 weeks prior to the onset of their chorea. 2 The obsessions and compulsions peak in intensity concomitantly with the chorea and wane away slowly over the ensuing months. A subgroup of patients with childhood-onset OCD was noted to have a similar symptom course. The OCD exacerbations occurred following GAS infections, accompanied by a cluster of comorbid symptoms, including emotional lability, separation anxiety, and attentional difficulties. The children were young (6–7 years old at symptom onset), predominantly male, and often had comorbid tics. 3 To indicate their shared clinical features (and presumed etiopathogenesis), the subgroup was identified by the acronym PANDAS—Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections. 3

The postulated pathophysiology of Sydenham chorea and PANDAS involves a series of factors, including the ‘rheumatogenic’GAS bacteria, genetic susceptibility, and abnormal immune responsivity. As shown in Figure 1, the proposed model not only provides a framework for understanding the etiology of OCD and tic disorders, but also for the development of novel intervention and prevention strategies. The major distinguishing feature of the PANDAS subgroup is the temporal association between neuropsychiatric symptom exacerbations and GAS infections—that is, positive (or rising) antistreptococcal antibody titers or a positive throat culture during neuropsychiatric symptom relapses and evidence of GAS negativity during periods of remission. 3 This one-toone correlation is necessary to distinguish GAS-triggered exacerbations of the PANDAS subgroup from the