Pathophysiology & Genetics of Chorea

Question	Answer
1. What is the definition and pathophysiology of Chorea?	Chorea is an involuntary, rapid, jerky, irregular, non-stereotyped, purposeless movement that flits continuously from one body part to another; in Sydenham's Chorea, it is caused by post-streptococcal autoimmune molecular mimicry where host antibodies against Group A $\beta$-hemolytic streptococcal (GABHS) N-acetyl-$\beta$-D-glucosamine cross-react with surface gangliosides and tubulin in neurons of the Caudate Nucleus and Subthalamic Nucleus of the Basal Ganglia, inducing hyperdopaminergic disinhibition of the thalamus and motor cortex.
2. Why is the latent period of Sydenham's Chorea unusually long (1 to 6 months)?	Unlike post-streptococcal arthritis or carditis (which appear in 2–3 weeks), it requires several months for cross-reactive anti-basal ganglia IgG antibodies to breach the blood-brain barrier, bind to neuronal receptors, and trigger neurotransmitter upregulation.
3. What is the anatomical neurocircuitry abnormality responsible for chorea?	Destruction or functional downregulation of the indirect pathway of the basal ganglia (caudate $\rightarrow$ globus pallidus externus $\rightarrow$ subthalamic nucleus), leading to loss of inhibition over the thalamocortical motor projections and generating excess involuntary motor output.
4. What are the common secondary causes of chorea in children?	1. Sydenham's Chorea (most common, ~70%); 2. Autoimmune (SLE, Antiphospholipid Syndrome, PANDAS); 3. Metabolic (Wilson disease, Glutaric aciduria type 1, Fahr disease / idiopathic basal ganglia calcification); 4. Drug-induced (Phenytoin, Methylphenidate, Haloperidol tardive chorea); 5. Genetic (Huntington disease, Benign Hereditary Chorea / NKX2-1 mutation).
5. What is PANDAS, and how does it relate to Sydenham's Chorea?	Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections (PANDAS) is characterized by acute-onset Obsessive-Compulsive Disorder (OCD) or motor/vocal tics following GABHS pharyngitis without true chorea, sharing a similar autoimmune basal ganglia pathogenesis.

Clinical Manifestations & Semiologic Signs

Question	Answer
1. Name and describe the 5 pathognomonic semiological signs of Chorea.	1. Pronator Sign: Hyperpronation of forearms turning palms outward when arms are raised above head; 2. Choreic Hand (Dish/Spoon hand): Wrist flexion with hyperextension of metacarpophalangeal joints on arm extension; 3. Milkmaid's Grip: Inability to maintain sustained grip, causing rhythmic milking contractions; 4. Chameleon / Jack-in-the-box Tongue: Tongue involuntarily retracts back into mouth within seconds of protrusion; 5. Hung-up (Gordon's) Reflex: Knee jerk extension is briefly suspended at its apex before returning pendularly.
2. Why does generalized hypotonia accompany choreic movements?	Basal ganglia disinhibition disrupts gamma motor neuron activity and muscle spindle resting sensitivity, causing marked flaccidity and passive joint hyperextensibility.
3. What is "Chorea Paralytica"?	A severe, extreme variant of Sydenham's chorea where profound muscle hypotonia and weakness completely mask the choreic movements, rendering the child completely bedridden, flaccid, and unable to speak or swallow (often mistaken for Guillain-Barré syndrome or myopathy).
4. Why do choreic movements disappear during sleep and worsen with emotional stress?	Involuntary basal ganglia motor discharges require cortical vigilance and awake motor readiness; during deep non-REM sleep, thalamocortical drive is suppressed, silencing choreic twitches; emotional stress upregulates central catecholamines, amplifying basal ganglia motor noise.
5. What is "Semi-purposeful Camouflage" in a choreic child?	When an involuntary choreic movement jerks the child's arm, the child instinctively converts the involuntary twitch into a socially acceptable purposeful act (e.g., smoothing the hair, adjusting eyeglasses, or scratching the ear) to hide the movement from peers.

Revised Jones Criteria & Rheumatic Workup

Question	Answer
1. Is the presence of Sydenham's Chorea alone sufficient to diagnose Acute Rheumatic Fever?	YES. According to the 2015 Revised AHA/Jones Criteria, Sydenham's Chorea is one of the two exceptional presentations (along with insidious indolent carditis) where a standalone clinical diagnosis of ARF can be made without requiring other major/minor criteria or documented evidence of preceding streptococcal infection, because of the long latency period during which serology often normalizes.
2. Why is 2D Echocardiography mandatory in every child with suspected isolated chorea?	Up to 30–50% of children presenting with "pure" Sydenham's chorea have subclinical rheumatic carditis (mitral regurgitation) detectable on echocardiography, which fundamentally changes their long-term secondary penicillin prophylaxis duration.
3. Why might ASO titres and acute phase reactants (ESR, CRP) be completely normal in Sydenham's Chorea?	Because chorea emerges 1 to 6 months after the acute streptococcal pharyngeal infection, by which time acute systemic inflammation has completely resolved and anti-streptolysin O titers have declined; testing Anti-DNase B yields a much higher positivity rate.
4. What are the 2015 Revised Jones Criteria Major Manifestations for Moderate-to-High Risk Populations?	1. Carditis (Clinical or Subclinical on Echo); 2. Polyarthritis (or Monoarthritis / Polyarthralgia); 3. Sydenham's Chorea; 4. Erythema Marginatum; 5. Subcutaneous Nodules.

Pharmacotherapy & Penicillin Prophylaxis Protocols

Question	Answer
1. What is the drug of choice for symptomatic control of choreic movements in Sydenham's Chorea?	Sodium Valproate ($15\text{–}30\text{ mg/kg/day}$ orally in 2–3 divided doses); it enhances central GABAergic inhibition in the basal ganglia and has high efficacy with minimal risk of extrapyramidal side effects compared to neuroleptics.
2. What second-line pharmacotherapies are used if Valproate is ineffective?	Haloperidol ($0.02\text{–}0.05\text{ mg/kg/day}$), Pimozide, or Carbamazepine ($10\text{–}20\text{ mg/kg/day}$); if haloperidol is used, monitor for acute dystonic reactions and sedation.
3. What is the role of Corticosteroids in Sydenham's Chorea?	Oral Prednisolone ($1\text{–}2\text{ mg/kg/day}$ for 2–4 weeks, followed by a 2-week taper) is indicated for severe or disabling chorea; it significantly shortens the duration of illness and hastens functional motor recovery by suppressing anti-basal ganglia autoimmune inflammation.
4. What is the exact regimen and duration of Secondary Penicillin Prophylaxis for Sydenham's Chorea?	Intramuscular Benzathine Penicillin G ($1.2\text{ million units}$, or $600,000\text{ units}$ if $<27\text{ kg}$) every 3 to 4 weeks: 1. If Chorea without Carditis: For 5 years after the last attack OR until 21 years of age (whichever is longer); 2. If Chorea with Carditis and residual valvular disease: For 10 years after the last attack OR until 25–40 years of age (often lifelong).

High-Yield VIVA TRAPs & Counter-Questions

Question	Answer
1. VIVA TRAP: The examiner asks: "A child presents with classical chorea, but the ASO titre is 120 IU/mL (normal) and Throat Culture is negative. Does this rule out Rheumatic Chorea?"	ABSOLUTELY NOT. Because of the 1–6 month latent period of Sydenham's chorea, the throat culture is almost always negative, and ASO titers have returned to baseline in $>50\%$ of cases. Under Revised Jones Criteria, chorea alone confirms ARF once other etiologies are ruled out.
2. VIVA TRAP: Examiner counter-question: "Should you perform an emergency Lumbar Puncture in a child presenting with typical choreiform movements?"	NO. In uncomplicated Sydenham's chorea, CSF is strictly normal (no cells, normal protein/glucose). Lumbar puncture is traumatic, unnecessary, and indicated only if acute meningoencephalitis, autoimmune encephalitis (Anti-NMDAR), or infectious chorea is suspected.
3. VIVA TRAP: "How do you clinically differentiate between Chorea and Motor Tics in an 8-year-old child?"	Chorea: Movements are non-repetitive, irregular, unpredictable, and flow continuously from joint to joint without any premonitory sensation; Tics: Movements are stereotyped, repetitive, coordinated jerks (e.g., eye blinking, head jerking) that are preceded by an irresistible inner premonitory urge and can be voluntarily suppressed for short intervals at the cost of mounting tension.
4. VIVA TRAP: "A 10-year-old with chorea and hepatomegaly is labeled as Sydenham's Chorea. What single bedside examination must you perform to avoid a fatal misdiagnosis?"	Slit-Lamp Examination for Kayser-Fleischer (KF) Rings in the cornea to rule out Wilson Disease (Hepatolenticular Degeneration). Treating Wilsonian chorea with penicillin instead of copper chelation leads to irreversible hepatic cirrhosis and neurological destruction.
5. VIVA TRAP: "A child's chorea completely resolves after 3 months of Valproate. Can you stop the monthly Benzathine Penicillin G injections?"	NEVER. Symptomatic resolution of chorea does NOT eliminate the lifelong risk of recurrent streptococcal pharyngitis triggering catastrophic recurrent rheumatic carditis; secondary penicillin prophylaxis MUST continue uninterrupted for the full mandatory duration (minimum until 21 years of age).