The purpose of this study is to find out whether an early three-day course of an oral steroid medication (dexamethasone) can improve the physical and mental recovery and wellbeing for children with Sydenham's chorea.

Sydenham's chorea is a condition that impacts approximately 12% of children with acute rheumatic fever. It is caused by inflammation in the brain following an abnormal immune response to Group A streptococcus bacterial infection. Sydenham's chorea is a movement disorder that causes children's faces, hands, and feet to move quickly and uncontrollably, and can also affect mood and concentration. The physical recovery from Sydenham's chorea can take two to six months but the mental recovery (e.g. mood and concentration) can take longer to resolve. Sydenham's chorea remains endemic in Māori, Pacific Islander, Aboriginal and Torres Strait Islander children in New Zealand and Australia.

There is limited evidence to direct treatment of Sydenham's chorea, and clinical practice differs widely around the world. Dexamethasone is an oral steroid which targets the abnormal immune response and successfully treats other immune-mediated brain disorders, with good tolerability.

TREAT-SC is a randomized, double-blinded, placebo-controlled trial which will investigate whether a three day course of oral dexamethasone safely and effectively treats the movement disorder and psychiatric symptoms of Sydenham's chorea. The trial will recruit 80 participants from study sites in Australia and New Zealand.

Aim: The aim of the trial is to determine whether an early, short course of oral dexamethasone is a safe and effective treatment to reduce morbidity associated with Sydenham's chorea in New Zealand and Australian children.

Objectives:

• The primary objective is to determine whether oral dexamethasone is an effective treatment to reduce Sydenham's chorea severity in New Zealand and Australian children at one month
• The secondary objectives are to determine whether oral dexamethasone is an effective treatment to reduce Sydenham's chorea severity at different time points, relapse and recurrence rates at three and 12 months, total hospital length of stay at three months, treatment failure at 14 days, use of adjunctive chorea treatments, Universidade Federal de Minas Gerais (UFMG) Sydenham's Chorea Rating Scale (USCRS) subscores, and psychiatric symptoms scored by the Strengths and Difficulties Questionnaire at one, three and 12 months. The safety of oral dexamethasone use will be assessed at study visits on days three and seven and at one month to monitor for any adverse events which may relate to dexamethasone use.

Research Design: TREAT-SC is a pragmatic parallel-group, double-blinded, placebo-controlled, 1:1 randomized efficacy trial comparing a three-day course of oral dexamethasone with placebo to treat Sydenham's chorea in New Zealand and Australian children. TREAT-SC will be a multi-site trial with participants recruited from hospitals in New Zealand and Australia.

Inclusion Criteria:

1. Sydenham's chorea of any severity diagnosed by a paediatrician or neurologist based on national ARF guidelines
2. Child or adolescents aged 4 years to <18 years of age

Exclusion Criteria:

1. Administered steroids or intravenous immunoglobulin since onset of the current Sydenham's chorea episode
2. Evidence of concomitant severe, acute infection
3. History of hypersensitivity to dexamethasone or its excipients
4. Pregnancy
5. Confirmed exposure of an unimmunised child to measles, mumps, rubella or chickenpox within the previous four weeks
6. Receipt of a live vaccine within the previous four weeks
7. Medical condition or treatment with medication which in the opinion of the trial investigators would make the child unsuitable for the trial

De-identified data would be shared with researchers conducting meta-analysis study if robust research plan is provided and request emailed to PI.

Blinding will be achieved by over-encapsulation of tablets so that placebo cannot be distinguished from dexamethasone