Kawasaki Disease (KD)

Kawasaki Disease (KD)

1. Introduction & Definition

Kawasaki Disease is an acute, self-limiting systemic vasculitis of unknown aetiology that predominantly affects infants and young children. It is the leading cause of acquired heart disease in children in developed countries. The primary threat is damage to the coronary arteries, leading to aneurysms, thrombosis, and potential long-term cardiac sequelae.

2. Aetiology & Epidemiology

• Aetiology: Unknown, but thought to be an abnormal immune response to an unidentified infectious trigger in genetically susceptible individuals.
• Epidemiology:
  • Peak incidence: 6 months to 5 years of age (80% of cases are <5 years).
  • Rare in <3 months and >8 years, but can occur and is often atypical.
  • Slight male predominance.
  • Higher incidence in children of Asian descent.

3. Clinical Features (The Diagnostic Challenge)

Diagnosis is clinical and based on the presence of a persistent fever plus a set of criteria. A high index of suspicion is crucial.

Classic Diagnostic Criteria (All 5 required, or 4/5 with Coronary Artery Disease on Echo):
Fever lasting ≥5 days (mandatory), plus 4 out of the following 5 principal clinical features:

1. Bilateral, Non-Exudative Conjunctival Injection: Typically sparing the limbus (area around the iris).
2. Oral Mucosal Changes: Injected/fissured lips, “strawberry tongue,” diffuse erythema of the oropharynx.
3. Polymorphous Rash: Usually truncal, can be maculopapular, erythema multiforme-like, or scarlatiniform.
4. Peripheral Extremity Changes:
   • Acute: Erythema of palms/soles, indurative oedema.
   • Convalescent (Days 10-14): Periungual desquamation (peeling).
5. Cervical Lymphadenopathy: ≥1 node >1.5 cm, usually unilateral, acute, and non-suppurative.

Incomplete (Atypical) Kawasaki Disease:
This is a common and critical scenario in the emergency department. A child has a fever for ≥5 days but does not meet the full classic criteria. It should be suspected in any infant with prolonged, unexplained fever and any of the principal features.

• Key Point from NICE: Incomplete KD is most common in infants <1 year, who are also at the highest risk for coronary artery complications.
• Diagnosis relies on a combination of clinical features and supplementary laboratory/echocardiographic findings.

4. Emergency Department Assessment (RCEMlearning )

The ED approach is to “Think KD” in any irritable infant or child with a prolonged fever.

History:

• Duration and pattern of fever (high-spiking, unresponsive to antibiotics/antipyretics).
• Detailed review of all 5 principal clinical features.
• Irritability is a hallmark feature.
• Other associated symptoms: diarrhoea, vomiting, abdominal pain, arthralgia/arthritis, cough.

Examination:

• Full set of observations: Look for signs of shock (Kawasaki Disease Shock Syndrome) or myocarditis.
• Comprehensive systems examination: Cardiorespiratory (murmur, gallop rhythm, tachycardia out of proportion to fever), abdominal, musculoskeletal, and neurological (irritability, aseptic meningitis).

Investigations (to support a diagnosis of Incomplete KD):
There is no diagnostic test. Investigations help support the clinical suspicion and rule out other causes.

• Bloods:
  • FBC: Normocytic anaemia, leukocytosis with neutrophilia, thrombocytosis (a late finding, often in week 2). Thrombocytopenia can occur in severe, shocked cases and is a risk factor for aneurysms.
  • CRP & ESR: Markedly elevated acute phase reactants (CRP >30, ESR often >40). Albumin may be low.
  • LFTs: May show elevated transaminases, sterile pyuria.
• ECG: May show signs of myocarditis (prolonged PR, ST/T wave changes).
• Echocardiogram (Echo): This is the key investigation. It must be performed urgently in any suspected case to look for coronary artery abnormalities (dilatation, aneurysms), pericardial effusion, or impaired ventricular function. A baseline echo should be performed at diagnosis and repeated at 2 and 6 weeks.

5. Differential Diagnosis (MUST be considered)

• Scarlet Fever / Streptococcal infection
• Viral Exanthems (Measles, Adenovirus, EBV)
• Toxic Shock Syndrome
• Staphylococcal Scalded Skin Syndrome
• Drug Hypersensitivity Reactions
• Juvenile Idiopathic Arthritis (Systemic onset)
• Leptospirosis / Rickettsial infections

6. Management in the ED (Based on NICE)

The cornerstone of management is timely treatment to reduce the risk of coronary artery damage.

1. Immediate Actions:
   • Refer immediately to the on-call Paediatric team.
   • Do not delay treatment awaiting echo results if clinical suspicion is high.
   • Admit the child for ongoing management.
2. First-Line Treatment:
   • Intravenous Immunoglobulin (IVIG): Single dose of 2g/kg, given over 10-12 hours.
   • High-Dose Aspirin: 30-50 mg/kg/day in divided doses (e.g., QDS).
   • Timing: IVIG is most effective when given within the first 10 days of illness, and should be administered as soon as the diagnosis is made. It can still be beneficial after day 10 if there is ongoing fever or evidence of ongoing inflammation.
3. Refractory Disease (10-20% of cases):
   • Defined as persistent or recrudescent fever ≥36 hours after completion of the first IVIG dose.
   • Management involves a second dose of IVIG or corticosteroids (e.g., IV Methylprednisolone), guided by a paediatric cardiology/rheumatology team.

7. Complications & Follow-up

• Coronary Artery Aneurysms: Occur in 15-25% of untreated cases, reduced to 2-5% with timely IVIG.
• Myocarditis, Pericarditis, Valvular Regurgitation.
• Long-term Follow-up: Is mandatory and based on the patient’s coronary artery status (Z-score). This involves lifelong cardiology follow-up for those with aneurysms, with management including low-dose aspirin, clopidogrel, or anticoagulants.

8. Key Take-Home Points for the Emergency Clinician

• Prolonged Fever + Rash = Think Kawasaki Disease.
• Incomplete forms are common, especially in infants. Do not be reassured by the absence of the full set of criteria.
• Irritability is a cardinal sign.
• Urgent Paediatric referral is mandatory. The goal is treatment with IVIG within 10 days of fever onset.
• An Echocardiogram is a critical part of the diagnostic workup for suspected cases.

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Disclaimer: This topic is a synthesis for educational purposes. Always consult the latest local trust guidelines, NICE CKS, and the British Society for Rheumatology (BSR) guidelines for the most current and definitive management protocols.