PANDAS

Pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections is a controversial hypothetical diagnosis for a subset of children with rapid onset of obsessive-compulsive disorder (OCD) or tic disorders.
Symptoms are proposed to be caused by group A streptococcal (GAS) and more specifically, group A beta-hemolytic streptococcal (GABHS) infections.
OCD and tic disorders are hypothesized to arise in a subset of children as a result of a post-streptococcal autoimmune process.
The proposed link between infection and these disorders is that an autoimmune reaction to infection produces antibodies that interfere with basal ganglia function, causing symptom exacerbations, and this autoimmune response results in a broad range of neuropsychiatric symptoms.
As the clinical spectrum of PANDAS appears to resemble that of Tourette syndrome / disorder (TS or TD), some researchers hypothesized that PANDAS and TS may be associated

Characteristic: Abrupt onset of symptoms, including motor or vocal tics, obsessions, or compulsions

PANDAS hypothesis is unconfirmed and unsupported by data, and two new categories have been proposed:
- PANS (pediatric acute-onset neuropsychiatric syndrome)
- CANS (childhood acute neuropsychiatric syndrome)
PANS is a hypothesized disorder characterized by the sudden onset of OCD symptoms or eating restrictions, concomitant with acute behavioral deterioration or neuropsychiatric symptoms.
CANS and PANS hypotheses include different possible mechanisms underlying acute-onset neuropsychiatric conditions, but do not exclude GABHS infections as a cause in a subset of individuals.
PANDAS, PANS, and CANS are the focus of clinical and laboratory research, but remain unproven.
Whether PANDAS is a distinct disease and differing from other cases of tic disorders or OCD is debated.
PANS eliminated tic disorders as a primary criterion and placed more emphasis on acute-onset OCD, while allowing for causes other than streptococcal infection.
PANS, CANS and PANDAS are also hypothesized to be autoimmune disorders.

The mechanism is hypothesized to be similar to that of rheumatic fever, an autoimmune disorder triggered by streptococcal infections, where antibodies attack the brain and cause neuropsychiatric conditions.
The molecular mimicry hypothesis is a proposed mechanism for PANDAS: this hypothesis is that antigens on the cell wall of the streptococcal 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 develop Sydenham's.

In some rheumatic fever patients, autoantibodies may attack heart tissue, leading to carditis, or cross-react with joints, leading to arthritis.
In PANDAS, it is believed that tics and OCD are 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. It is thought that similar to Sydenham's, the antibodies cross-react with neuronal brain tissue in the basal ganglia to cause the tics and OCD that characterize PANDAS.

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