Controversy has raged concerning whether or not streptococcal infection can be implicated in the genesis of Tourette syndrome or obsessive-compulsive disorder (OCD). A recent study suggests that there is no causal correlation. Small studies did find a correlation between strep throat and OCD, but a larger study involving 255 participants between the ages of 2 and 25 did not show a correlation. Of the group, 129 were diagnosed with OCD and 126 were diagnosed with Tourette syndrome. The researchers compared both groups with 4,519 of similar ages who lacked these problems.
Approximately 15 percent in the OCD group had been exposed to a possible strep infection within two years. The same was true, however, of those without OCD. Those with Tourette syndrome had a 10 percent chance of having been diagnosed with the disease within two years of diagnosis.
Nevertheless, some researchers believe that OCD may be the result of an autoimmune disease, in at least some cases. These researchers think that the streptococcal infection may trigger an autoimmune response whose biological pathway is similar to that of Sydenham’s chorea. Those who begin to exhibit OCD or tics following streptococcal infections are described as having been afflicted with “pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections,” or PANDAS. The researchers argue that neuorimaging studies suggest increased volume in the basal ganglia, and it is believed that there is a cross-reaction of streptococcal antibodies with basal ganglia tissue. That is, antistreptococcal antibodies are believed to have cross-reacted with tissue from the basal ganglia. Indeed, OCD is thought to be caused by basal ganglia dysfunction.
Those with PANDAS have been found to have significantly elevated antineuronal antibodies. This is true of related neuropsychiatric disorders in such children. An MRI study of participants with PANDAS have higher antistreptococcal antibodies, and this was correlated with increased basal ganglia volumes in children with either OCD or ADHD. This is what one would expect from an autoimmune-mediated inflammation of this part of the brain. Nevertheless, it remains unclear as to whether this autoimmune response is specific to OCD only or if it may have relevance to other childhood psychiatric problems. Indeed, some have suggested that there is a significant correlation between high antistreptococcal antibody titres and a diagnosis of ADHD. It is possible that some children have be genetically predisposed to develop PANDAS due to a genetic predisposition to formation of antistreptococcal antibodies which cross-react with neuronal proteins or neurotransmitter imbalance. It is also possible that they suffer from an immune dysregulation.
Higher rates of OCD have been found in first-degree relatives of children diagnosed with PANDAS, which is typical of what is found in relatives with OCD. There therefore may be a degree of genetic vulnerability to PANDAS. It is also possible that cytokine levels may have something to do with the genesis of OCD. Some studies suggest that children with OCD exhibit a skewing toward type 1 cytokine production in their cerebrospinal fluid.