Chorea Differential and Sydenham Chorea
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Direct answer
Chorea is brief, irregular, dance-like involuntary movement that flows from one body part to another. Sydenham chorea is its common acquired form in children, following group A streptococcal infection through molecular mimicry, and it is usually self-limiting over weeks to months. Huntington disease, drug-induced chorea and Wilson disease form the main differential, and the family and drug histories usually decide between them.
What you must remember
- Huntington disease: autosomal dominant, caused by an expanded CAG repeat in the HTT gene on chromosome 4, with chorea, cognitive decline and psychiatric change.
- Sydenham chorea: post-streptococcal chorea in children, typically aged 5 to 15 years, appearing weeks to months after pharyngitis.
- Emotional lability: a common accompaniment of Sydenham chorea, often alongside clumsiness and jerky, purposeless limb movements.
- Jones criteria: chorea is a major criterion for acute rheumatic fever, and when it is the sole manifestation it can establish the diagnosis without evidence of preceding streptococcal infection, because the latent period is long and the antistreptolysin O titre may have normalised.
- Secondary prophylaxis: benzathine penicillin G is given to prevent recurrence of rheumatic fever after an episode of Sydenham chorea.
- Drug-induced chorea: levodopa, dopamine agonists and amphetamines increase dopaminergic activity and cause chorea that resolves when the drug is stopped.
- Hemiballismus: violent flinging of one limb, from a lesion of the contralateral subthalamic nucleus, most often from a stroke.
Comparing the main causes of chorea
A 9-year-old girl has three weeks of clumsiness, emotional lability and jerky hands after a sore throat. The table compares her picture with the two main alternatives in the differential.
| Feature | Huntington disease | Sydenham chorea | Drug-induced chorea |
|---|---|---|---|
| Typical age | Adult onset, commonly 30 to 50 years | Children, about 5 to 15 years | Any age |
| Trigger | Inherited CAG repeat expansion | Group A streptococcal infection | Dopaminergic drug |
| Course | Progressive, with dementia | Self-limiting over weeks to months | Resolves when the drug stops |
| Key test | HTT CAG repeat testing | Clinical diagnosis, echocardiography, streptococcal serology if available | Drug history |
| Treatment | Dopamine blockade or a VMAT2 inhibitor | Penicillin prophylaxis and symptomatic relief | Stop or reduce the drug |
A childhood chorea after a sore throat should prompt the Sydenham question, while adult-onset chorea with a family history points to Huntington disease. Drug-induced chorea is the simplest to reverse, which is why a careful drug history comes first in every case, before any genetic or serological test is ordered.
Where the exam tries to catch you
The stem usually provides one clue in the history that changes the diagnosis.
- Trap: assuming every childhood chorea is idiopathic Correct: post-streptococcal Sydenham chorea is the commonest acquired cause in children and needs echocardiography and streptococcal serology, though normal serology does not exclude it.
- Trap: stopping prophylaxis once the chorea settles Correct: secondary prophylaxis against rheumatic fever recurrence remains necessary after an episode.
- Trap: dismissing a family history of chorea with dementia as psychiatric Correct: an autosomal dominant pattern with cognitive decline suggests Huntington disease, confirmed by CAG repeat testing.
- Trap: blaming hemiballismus on a peripheral cause Correct: violent flinging of one limb points to a contralateral subthalamic nucleus lesion.
Frequently asked questions
Which test supports a diagnosis of Sydenham chorea?
Sydenham chorea is a clinical diagnosis, and raised antistreptolysin O or anti-DNase B titres support recent group A streptococcal infection, though they may be normal because of the long latent period. Echocardiography is essential to look for carditis.
How long does Sydenham chorea usually last?
Sydenham chorea is self-limiting, and most children recover over weeks to months. Symptomatic drugs such as haloperidol or valproate are reserved for severe or disabling movements, while the course is monitored closely.
What is the genetic basis of Huntington disease?
Huntington disease is caused by an expanded CAG trinucleotide repeat in the HTT gene on chromosome 4, and it is inherited in an autosomal dominant pattern. Longer repeats are associated with earlier onset, and genetic testing confirms the diagnosis.
Which drugs cause chorea?
Levodopa, dopamine agonists and amphetamines can cause chorea by increasing dopaminergic activity. Stopping or reducing the offending drug usually resolves the movements, which makes a careful drug history essential.
Where does hemiballismus arise in the brain?
Hemiballismus arises from a lesion of the contralateral subthalamic nucleus, most often from a stroke. It causes violent, flinging movements of one limb and is a severe form of chorea.