The dance of the immune system: why children move like marionettes

Health · Published 18 October 2026 Swipe more like this →

In short: Imagine a child suddenly developing erratic, writhing movements that resemble dancing. This neuropsychiatric disorder, known as Sydenham's chorea, occurs when an immune response to a common strep throat infection mistakenly attacks the brain. It creates involuntary motions in the limbs and face, often appearing months after the initial bacterial infection.

Sydenham's chorea is a neuropsychiatric disorder characterized by rapid, uncoordinated jerking movements, often affecting the face, hands, and feet. It is primarily an autoimmune response triggered by an infection with Group A beta-hemolytic Streptococcus, the same bacteria responsible for strep throat and rheumatic fever. The condition typically emerges in children aged 5 to 15, appearing a few weeks to six months after the initial infection. While it is the most common form of acquired chorea, it is relatively rare in developed nations due to the widespread use of early antibiotics.

The underlying mechanism is believed to be 'molecular mimicry.' The immune system produces autoantibodies to fight the streptococcal infection, but these antibodies cross-react with the host's own tissues, specifically the cerebral basal ganglia. Research has identified cross-reactive antigens like the M protein and N-acetyl-beta-D-glucosamine. While dopamine receptor autoantibodies have been reported to correlate with symptoms, scientists are still investigating whether these are the direct cause of the movement disorder or merely a byproduct of the immune response.

Clinically, the condition is distinctive. Patients may exhibit the 'milkmaid sign' (fluctuating grip strength), 'jack-in-the-box' tongue (involuntary sliding of the tongue), or 'piano-playing' finger movements. Beyond motor issues, it can cause emotional lability, anxiety, and attention deficits. Diagnosis can be challenging because biological tests like Anti-DNAse B or Anti-streptolysin O may be negative if the infection occurred months prior. In some cases, advanced imaging like FDG PET/CT is required to visualize alterations in the caudate nucleus or putaminal enlargement.

Management focuses on clearing the remaining bacteria with penicillin and managing symptoms with medications like sodium valproate. While steroids have shown success in reducing the duration of severe symptoms in some trials, the primary goal is preventing cardiac complications. Although most children make a full recovery, about 16–40% of cases may recur, sometimes years later. Long-term neuropsychiatric difficulties, including obsessive-compulsive disorder and executive function disturbances, are also increasingly recognized as potential lingering effects.

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