Kawasaki Disease for NEET PG: The Five Criteria, the 10-Day IVIG Window and the Coronary Risk

Kawasaki disease (KD) is an acute vasculitis of early childhood, and in developed countries it is the most common cause of acquired heart disease in children. The diagnosis is clinical, there is no confirmatory test, and treatment is time-sensitive, so the criteria, the treatment window and the coronary risk have to be learned together. This post takes them in that order, then covers the incomplete form, the vaccine rule after IVIG and the conditions that mimic KD.

What Kawasaki Disease Is

KD is a systemic inflammation of medium-sized arteries, mainly the muscular arteries, and the coronary arteries are the clinically important target. The cause is unknown. A widely held view is that an unidentified trigger acts in a genetically susceptible child, and an infectious trigger has been proposed but not confirmed.

The pathology comes in three linked processes. Necrotizing arteritis is a neutrophilic process that is complete within 2 weeks of fever onset, and it is the one that can lead to aneurysms. Subacute and chronic vasculitis, with lymphocytes, plasma cells and eosinophils, begins in the first 2 weeks and can persist for months to years in a small subset of patients. Luminal myofibroblastic proliferation starts at the same time and can cause progressive arterial stenosis.

The epidemiology is worth a quick list:

• Age: it predominantly affects children under 5 years, and about 76% of affected children in the continental United States fall in that group. The mean age in the United States is about 3 years, and infants under 6 months can be affected, sometimes with prolonged fever and irritability as the only signs.
• Sex: boys outnumber girls by about 1.5 to 1.7 to 1 in the United States.
• Geography: the incidence is highest in Japan, and within Hawaii it is highest in children of Japanese descent.
• Season: in the continental United States, cases are more common in winter and early spring.
• Recurrence: uncommon, at about 3% in one Japanese study and about 1.7% in US surveillance data.

The Diagnostic Criteria: Fever Plus Four of Five (CRASH and Burn)

Classic or complete KD needs fever for at least 5 days plus at least 4 of 5 principal features; with 4 or more features, especially redness and swelling of the hands and feet, the diagnosis can already be made on day 4 of fever. The mnemonic CRASH and burn covers them: Conjunctivitis, Rash, Adenopathy, Strawberry tongue (oral changes) and Hand and foot changes, with the burn standing for the fever of 5 days or more.

Feature	What to look for	Timing or clue
Conjunctivitis	Bilateral bulbar conjunctival injection without exudate	Often spares the limbus, the avascular zone around the iris
Oral changes	Red, cracked lips, strawberry tongue, or redness of the oral and pharyngeal mucosa	Oral ulcers or pharyngeal exudate point to another diagnosis
Rash	Maculopapular, diffuse erythroderma, or erythema multiforme-like, with accentuation in the groin	Usually within 5 days of fever onset; no vesicles or bullae
Hand and foot changes	Redness and swelling of the hands and feet in the acute phase	Peeling around the nails begins 2 to 3 weeks after fever onset; Beau's lines can appear at 1 to 2 months
Cervical adenopathy	Usually one-sided, at least 1.5 cm, in the anterior cervical triangle	The least common of the five principal features

Several findings support the diagnosis without being criteria: extreme irritability, sterile pyuria, aseptic meningitis, gallbladder hydrops, arthritis, anterior uveitis and mildly raised liver enzymes. In a child who has had BCG, redness and induration at the old BCG site is a recognized supportive finding, which makes it a useful clue in India, where BCG is given at birth (see the immunization schedule post).

The laboratory picture reflects inflammation. ESR and CRP are raised in nearly all patients, CRP normalizes faster than ESR, and IVIG itself raises the ESR. The white count is high with neutrophil predominance, and a normocytic anemia is common. Platelets are the timing trap: thrombocytosis typically appears in the second week, peaks in the third week at a mean of about 700,000 per cubic millimeter, and settles by 4 to 6 weeks. Albumin is often low, transaminases are mildly to moderately raised in 40% to 60% of patients, sodium can be low, and pyuria is present in up to 80%.

Picture an illustrative case: a 3-year-old with 6 days of fever that has not responded to antibiotics. He is irritable, with red cracked lips, a strawberry tongue, red eyes without discharge on both sides, swollen red hands and a rash on the trunk that is most marked in the groin. That is fever plus four of the five features, so he meets the criteria for classic KD without any specific test, and treatment starts as soon as the diagnosis is made.

Incomplete Kawasaki Disease: When the Criteria Fall Short

Incomplete KD applies to a child with prolonged unexplained fever of 5 days or more and only 2 or 3 compatible features, or to an infant with fever for 7 days or more and no other explanation. The next step is laboratory: a CRP of 3.0 mg/dL or more, an ESR of 40 mm/hr or more, or both, keeps the diagnosis in play.

Treatment then follows if either of these is true:

• The echocardiogram is positive: the left anterior descending or right coronary artery has a Z score of 2.5 or more, an aneurysm is seen, or at least 3 other suggestive features are present, such as reduced left ventricular function, mitral regurgitation, pericardial effusion or Z scores of 2 to 2.5.
• At least 3 supplementary laboratory findings are present: anemia for age, platelets of 450,000 per cubic millimeter or more after day 7 of fever, albumin of 3.0 g/dL or less, a raised ALT, a white count of 15,000 per cubic millimeter or more, or 10 or more white cells per high-power field in the urine.

Consider an illustrative infant of 9 months with 8 days of fever, red cracked lips and a rash, but no conjunctivitis, no hand or foot changes and no adenopathy. His CRP is well above 3.0 mg/dL, and he has platelets above 450,000 after day 7, albumin below 3.0 g/dL and a raised ALT. He does not meet the classic criteria, but a raised CRP plus 3 supplementary findings is enough to treat.

Treatment: IVIG, Aspirin and the 10-Day Window

IVIG is the treatment that changed the outlook. The dose is 2 g/kg as a single infusion, usually over 10 to 12 hours (the 2024 AHA update says 8 to 12 hours), given with aspirin, within 10 days of fever onset and as soon as the diagnosis is made. Untreated, about 25% of children develop coronary aneurysms; with timely IVIG that falls to about 4% to 5%. After day 10, IVIG is still reasonable if there is persistent unexplained fever or coronary abnormalities, together with ongoing inflammation, meaning a CRP above 3.0 mg/dL or a raised ESR.

Aspirin is used in two phases. In the acute febrile phase it is given every 6 hours, at a high dose of 80 to 100 mg/kg/day (the traditional US dose) or a moderate dose of 30 to 50 mg/kg/day (the usual dose in Japan and Western Europe), and the dose has not been shown to change coronary outcomes. Many centers step down once the child has been afebrile for 48 to 72 hours, while others continue until day 14 and at least 48 to 72 hours after the fever stops.

The low-dose phase is 3 to 5 mg/kg/day as an antiplatelet agent, continued until there are no coronary changes at 6 to 8 weeks after illness onset. If coronary abnormalities persist, it may continue much longer, and ibuprofen should generally be avoided in a child with aneurysms who is taking aspirin.

IVIG resistance is fever that persists, or returns, 36 hours or more after the infusion ends, and it affects about 10% to 20% of patients. Options include a second IVIG dose, corticosteroids, infliximab and cyclosporine, and in refractory cases etanercept, anakinra or cyclophosphamide. In the RAISE trial, children predicted to be IVIG-resistant received prednisolone 2 mg/kg/day for 5 days, followed by an oral taper, in addition to IVIG, and had fewer coronary abnormalities than those given IVIG alone. The trial was done in Japan, and the approach has not been validated in non-Japanese populations.

Return to the 3-year-old: IVIG and aspirin start on day 6 of fever. If he is still febrile 36 hours after the infusion ends, he is IVIG-resistant and further therapy is required. If the fever settles, aspirin steps down in a center that does so at 48 to 72 hours afebrile, and the first follow-up echocardiogram falls 1 to 2 weeks after treatment.

Coronary Involvement and Follow-Up

Coronary involvement is graded by Z score, which expresses the coronary artery diameter relative to body size. The categories are:

Category	Definition
No involvement	Z score always below 2
Dilation only	Z score from 2 to below 2.5; or initially below 2 with a fall of 1 or more during follow-up
Small aneurysm	Z score from 2.5 to below 5
Medium aneurysm	Z score from 5 to below 10, and absolute dimension below 8 mm
Large or giant aneurysm	Z score of 10 or more, or absolute dimension of 8 mm or more

Echocardiography is done when KD is suspected and, in uncomplicated cases, repeated 1 to 2 weeks and 4 to 6 weeks after treatment, which is the AHA 2017 schedule; the 2024 update makes the 4 to 6 week study conditional in children whose coronary arteries stay normal. A child with a Z score above 2.5 and evolving disease is scanned at least twice a week until the dimensions stop progressing. Coronary dilation is not usually detected until after the first week of illness, so one normal early scan does not close the question.

The dangerous window is later than most people expect. Peak mortality falls 15 to 45 days after fever onset, giant aneurysms can rupture in the first 2 to 3 weeks, and myocardial infarction can occur years later; many fatal and nonfatal infarctions in young adults have been attributed to missed KD in childhood.

Other complications to know:

• KD shock syndrome: about 5% of children in the United States present with hypotension and cardiovascular collapse, and they carry a higher risk of IVIG resistance, coronary abnormalities and mitral regurgitation.
• Macrophage activation syndrome: rare, and often associated with IVIG resistance.
• Cardiac inflammation: myocarditis, pericardial effusion, valve regurgitation and arrhythmias can occur alongside the coronary changes.

The Vaccine Rule After IVIG

High-dose IVIG carries passive antibodies that can blunt the response to live vaccines. The 2017 American Heart Association statement advises deferring measles, mumps and varicella vaccines for 11 months after high-dose IVIG, and the 2024 update refers to all live vaccines, naming measles, mumps, rubella and varicella. In practice the interval applies to measles-containing (MMR or MR) and varicella vaccines, and CDC guidance exempts rotavirus and yellow fever vaccines. Measles vaccine can be given earlier if the exposure risk is high, with revaccination at least 11 months after IVIG if the antibody response is inadequate.

India's schedule gives the first measles-rubella dose at 9 months, and MR contains live measles virus, so the same logic applies to a child treated before that dose is due. An infant treated with IVIG at 7 months would reach 9 months still inside the 11-month window, so the timing of the dose should be confirmed against current national guidance.

Children aged 6 months and older, and their family members, should receive the seasonal influenza vaccine, and a child taking aspirin should receive the inactivated vaccine only. For varicella, the manufacturer advises avoiding salicylates for 6 weeks after vaccination, so that risk is weighed against the risk of wild-type varicella.

Look-Alikes: What Else Causes Fever, Rash and Red Eyes

Because there is no confirmatory test, the look-alikes have to be considered. The differential includes measles, adenovirus and enterovirus infections, scarlet fever and toxic shock syndrome, drug hypersensitivity reactions including Stevens-Johnson syndrome, and systemic-onset juvenile idiopathic arthritis. Detecting a respiratory virus does not by itself exclude KD, but exudative pharyngitis and conjunctivitis with a positive adenovirus test make KD extremely unlikely.

Multisystem inflammatory syndrome in children (MIS-C), the post-COVID-19 inflammatory syndrome, is the newer mimic. The table summarizes the differences reported in published comparisons.

Feature	Kawasaki disease	MIS-C
Typical age	Mostly under 5 years; infants under 6 months can be affected	School age, with a median of about 7 to 9 years
Mucocutaneous and gastrointestinal features	Conjunctival injection, oral changes and rash are more common; gastrointestinal symptoms are less prominent	Gastrointestinal symptoms such as abdominal pain, vomiting and diarrhea are prominent; mucocutaneous signs are less common
Heart	Coronary dilation or aneurysm is the hallmark	Left ventricular dysfunction and pericardial effusion are more prominent; coronary dilation occurs in a minority and usually regresses within weeks
Blood counts	Neutrophilia, with thrombocytosis after the first week	Lymphopenia and thrombocytopenia are more pronounced; neutrophilia occurs in both and is often higher in MIS-C
Inflammatory markers	Typically lower CRP and ferritin	Higher CRP and ferritin

High-Yield Traps and One-Line Answers

• Fever for at least 5 days plus 4 of 5 features is classic KD, and with 4 or more features, especially hand and foot changes, the diagnosis can be made on day 4.
• Incomplete KD is fever for 5 days or more with 2 or 3 features, or an infant with fever for 7 days or more, plus a CRP of 3.0 mg/dL or more and/or an ESR of 40 mm/hr or more. Treat if the echocardiogram is positive or at least 3 supplementary laboratory findings are present.
• IVIG is 2 g/kg as a single infusion within 10 days of fever onset. Aspirin does not replace it.
• Aspirin is given at a high or moderate dose in the acute phase (80 to 100 or 30 to 50 mg/kg/day), then 3 to 5 mg/kg/day until the coronary arteries are normal at 6 to 8 weeks.
• IVIG resistance means fever 36 hours or more after the infusion ends.
• Thrombocytosis belongs to weeks 2 and 3, not the first week, and peeling around the nails starts at 2 to 3 weeks.
• Echocardiography at diagnosis, then 1 to 2 weeks and 4 to 6 weeks after treatment; aneurysms are the late danger.
• Measles-containing (MMR or MR) and varicella vaccines wait 11 months after high-dose IVIG, while rotavirus and yellow fever vaccines are not held back. The influenza vaccine for a child on aspirin must be inactivated.
• Oral ulcers, pharyngeal exudate, or bullous or vesicular skin lesions argue against KD.
• In developed countries KD is the most common cause of acquired heart disease in children. If rheumatic heart disease is also an option, the wording of the stem decides.

For the structural side of the pediatric heart, read the Tetralogy of Fallot post. Pediatrics makes up about 5% to 7% of the paper in our subject-wise weightage analysis, so it repays systematic revision, and the quickest way to lock this topic in is through questions in Reflex practice.