PANDAS

# Background
PANDAS is an abbreviation for Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections. This diagnosis is used to describe a set of children who are thought to have developed obsessive-compulsive disorder (OCD) and/or tic disorders such as Tourette syndrome following group A beta-hemolytic streptococcal (GABHS) infections such as "strep throat" and scarlet fever. Whether this condition exists is controversial and has been disputed, as some scientists think this sub-set of patients do not differ in any significant way from the remainder of the patient population and that infections do not increase the risk of Tourette syndrome. Consequently, the PANDAS model is a complex and rapidly-moving area of medical research.  PANDAS is currently not listed as a diagnosis in the ICD or DSM.

# Identification
Children with PANDAS are clinically identified by dramatic, "overnight" onset of symptoms, including motor or vocal tics, obsessions, and/or compulsions, although this has not been consistent in all studies. Indeed some studies have shown no acute motor exacerbations among clinically defined PANDAS subjects whilst others have shown a profound one.
In addition to the motor symptoms, it is also thought that children may have psychiatric manifestations, becoming moody, irritable or show concerns about separating from parents or loved ones. In the PANDAS model, this abrupt onset is thought to be preceded by a strep throat infection. As the clinical spectrum of PANDAS appears to resemble that of Tourette's syndrome, some researchers hypothesize that PANDAS and Tourette's may be associated. This idea is controversial and a focus for current research.
Concerns have been raised that PANDAS may be overdiagnosed, as nearly a third of patients diagnosed with PANDAS by community physicians did not meet the criteria when examined by specialists, suggesting that the PANDAS diagnosis is conferred by community physicians without scientific evidence.

# Proposed mechanism
At present, whether the group of patients diagnosed with PANDAS have developed tics and OCD through a different mechanism (pathophysiology) than seen in other people diagnosed with Tourette syndrome is unclear. However, researchers at the NIMH are pursuing a hypothesis that the mechanism is similar to that of rheumatic fever, an autoimmune disorder triggered by streptococcal infections, where antibodies attack the brain and cause neuropsychiatric conditions.
In every bacterial infection, the body produces antibodies against the invading bacteria, and the antibodies help eliminate the bacteria from the body. However in rheumatic fever, the antibodies mistakenly recognize and "attack" the heart valves, joints, and/or certain parts of the brain. This phenomenon is called "molecular mimicry", which means that antigens on the cell wall of the strep. bacteria are similar in some way to the proteins of the heart valve, joints, or brain. Because the antibodies set off an immune reaction which damages those tissues, the child with rheumatic fever can get heart disease (especially mitral valve regurgitation), arthritis, and/or abnormal movements known as Sydenham's chorea or "St. Vitus Dance". In PANDAS, it is believed that Tourette syndrome is produced in a similar manner. One part of the brain that may be affected in PANDAS is the basal ganglia, which is believed to be responsible for movement and behavior. Thus, the antibodies damage the brain to cause the tics and OCD that characterize Tourette syndrome, instead of Sydenham's chorea. However, current data neither disprove nor support this hypothesis, indeed one recent study found no association between streptococcal infections and the risk of PANDAS symptoms.

# Experimental treatments
As both the PANDAS diagnosis and the hypothesis that symptoms in this subgroup of patients are caused by infection are controversial, anti-infective treatments for Tourette syndrome are experimental.  According to the Advisory Boards of the Tourette Syndrome Association and the NIH, this diagnosis has engendered the use of dangerous and unproven treatment methodologies for children with tics and OCD, such as intravenous immunoglobulin (IVIG), plasma exchange, and the use of prophylactic antibiotics for the prevention of streptococcal infections.
The results from these experimental treatments have been mixed, although an initial study with 37 children found no effect of antibiotic treatment on either infection rate or obsessive-compulsive or tic symptom severity, a smaller study on twenty-three children later suggested that antibiotics were beneficial. However, the methods in the latter study have been criticized.