Overview
Definition:
Kawasaki disease (KD) is an acute febrile illness of unknown etiology that causes vasculitis, primarily affecting medium-sized arteries
Incomplete KD refers to cases that do not meet the classic diagnostic criteria but still have a high suspicion for the disease.
Epidemiology:
Primarily affects infants and young children, with a peak incidence between 6 months and 5 years
More common in males and individuals of East Asian descent
Incidence varies globally, with higher rates reported in Japan
Incomplete KD is more frequent in infants under 1 year.
Clinical Significance:
Prompt diagnosis and treatment are crucial to prevent coronary artery abnormalities (aneurysms, ectasia), which can lead to serious cardiovascular complications
In infants, the atypical presentation of incomplete KD poses a diagnostic challenge, increasing the risk of delayed treatment and adverse outcomes.
Clinical Presentation Infants
Symptoms:
Prolonged fever (≥5 days) is the hallmark
Other symptoms may be subtle or absent in infants
May include irritability, poor feeding, a faint rash, or transient conjunctival injection.
Signs:
Physical exam findings in infants can be nonspecific: diffuse erythematous rash (often maculopapular), bilateral non-purulent conjunctival injection, fissured or red lips, strawberry tongue, cervical lymphadenopathy (usually >1.5 cm, unilateral)
Extremity changes (erythema/edema of hands/feet, later desquamation) may be delayed or absent.
Diagnostic Criteria:
Diagnosis of incomplete KD is considered in a febrile infant (≥5 days) who does not meet the criteria for classic KD but shows at least two of the following: conjunctival injection, rash, oral mucosal changes, extremity changes, or cervical lymphadenopathy
Echocardiographic findings may support the diagnosis.
Diagnostic Approach Infants
History Taking:
Focus on the duration and pattern of fever
Inquire about feeding difficulties, irritability, any rash noted, and recent infections
Family history of autoimmune diseases or vasculitis is relevant.
Physical Examination:
A thorough examination is paramount, looking for subtle signs: conjunctival injection, pharyngeal erythema, lip changes, any rash, cervical lymphadenopathy
Assess extremities for edema or erythema
Monitor vital signs closely.
Investigations:
Laboratory tests: Elevated ESR and CRP are common but nonspecific
Leukocytosis with a left shift may be present
Anemia of chronic inflammation can occur
Thrombocytosis may develop in the second week
Urinalysis may show pyuria
Echocardiography is essential to assess for coronary artery dilation or aneurysms, even in suspected incomplete KD.
Differential Diagnosis:
Viral exanthems (enterovirus, adenovirus), scarlet fever, staphylococcal/streptococcal toxic shock syndrome, drug reactions, rickettsial infections, leptospirosis, measles, atypical measles, systemic juvenile idiopathic arthritis, meningococcemia, Yersinia infection.
Management Infants
Initial Management:
Prompt treatment is vital
In infants with suspected incomplete KD and fever ≥5 days, especially with inflammatory markers elevated, initiate treatment
The primary goal is to prevent coronary artery abnormalities.
Medical Management:
Intravenous immunoglobulin (IVIG) at 2 g/kg over 10-12 hours, given as a single infusion
Aspirin therapy: Low-dose (3-5 mg/kg/day) for antiplatelet effect once fever subsides
Higher dose (80-100 mg/kg/day) during the febrile phase for anti-inflammatory effect, then reduced
Monitor for resistance to IVIG.
Supportive Care:
Maintain hydration and adequate nutrition
Monitor vital signs and clinical status closely
Provide antipyretics for comfort if fever persists
Counsel parents on signs of cardiac complications and when to seek immediate medical attention.
Follow Up Management:
If fever persists >48 hours after IVIG, consider a second dose of IVIG
Follow-up echocardiography is crucial at 2-3 weeks and 6-8 weeks post-diagnosis, or earlier if initial findings are abnormal.
Complications
Early Complications:
Myocarditis, pericarditis, valvulitis, arrhythmias
Coronary artery aneurysms or ectasia can develop within days to weeks.
Late Complications:
Coronary artery thrombosis, myocardial infarction, stenosis of coronary arteries, sudden cardiac death
Rupture of giant aneurysms.
Prevention Strategies:
Early recognition and timely administration of IVIG within the first 10 days of illness (ideally by day 7) significantly reduce the risk of coronary artery abnormalities
Careful monitoring for signs of cardiac involvement is essential.
Key Points
Exam Focus:
Incomplete KD in infants is a diagnostic challenge due to nonspecific symptoms
Prolonged fever ≥5 days is the primary clue
Echocardiography is critical for diagnosis and management
IVIG and aspirin are the cornerstones of therapy
Risk of coronary artery aneurysms is high if untreated.
Clinical Pearls:
Always consider KD in an infant with unexplained prolonged fever, even with few classic signs
Use a scoring system (e.g., Likoff criteria) to aid in decision-making for suspected incomplete KD
Aggressive management is key to preventing cardiac sequelae.
Common Mistakes:
Delaying treatment due to incomplete criteria, mistaking KD for a simple viral illness, inadequate cardiac evaluation, or insufficient follow-up of echocardiographic findings.