When a patient presents with a history, examination, and laboratory findings consistent with KD without meeting the typical diagnostic standard, incomplete KD should be considered. The term “incomplete” is favored over “atypical” for this pre-sentation, because these patients are otherwise similar to other patients with KD. Patients with fever for five or fewer days and fewer than four principal features can be diagnosed as having KD when coronary artery disease is detected by two-dimensional echocardiography or coronary angiography (see Figure 1, p. 10). In the presence of four or more principal criteria, KD can be diagnosed before day four of the illness by an experienced clinician.6 Features less consistent with KD include the presence of exudative conjunctivitis, exudative pharyngitis, discrete intraoral lesions, bullous or vesicular rash, or generalized adenopathy.
If clinical features are consistent with KD, further risk stratification with erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) will determine whether patients are followed daily (if low) or if supplementary laboratory tests should be done (see Figure 1, p. 10). If three or more of supplementary laboratory criteria are present (albumin ≤3.0 g/dL, anemia for age, elevation of alanine aminotransferase (ALT), platelet count after seven days is 450 000/mm3 or greater, white blood cell count is 15,000/mm3 or greater, and urinary sediment containing 10 white blood cells/high-power field or more), echocardiogram should be performed and treatment initiated if abnormal.6
Young infants are more likely to manifest an incomplete presentation of KD, with a polymorphous rash being the most common symptom other than fever in this age group.7 Acute phase symptoms were also more likely to progress rapidly in this age group, with a higher risk of developing cardiac sequelae.8 As a result, any infant under the age of six months with fever for more than seven days and no other clear etiology should be evaluated for KD even in the absence of other diagnostic criteria.9
Other clinical manifestations of KD may include:
- Irritability: more notable in KD than in other febrile illnesses;
- Arthralgia and arthritis: may occur in the first week;
- Gastrointestinal complaints and findings: hepatomegaly, jaundice; and
- Abnormal chest X-ray findings: may be present in as many as 15% of patients.
Echocardiogram – view of left anterior descending artery
Cardiovascular manifestations can be prominent in the acute phase of KD and are the leading cause of long-term morbidity and mortality. Coronary artery aneurysms occur in 20% of affected children with KD. Other cardiovascular complications include myocardial ischemia and ensuing depressed contractility and arrhythmias, as well as vascular obstruction in peripheral arteries.
A subset of KD patients develops hemodynamic instability requiring management in a critical care setting. This phenomenon has been named Kawasaki disease shock syndrome, where hemodynamic instability is not related to administration of intravenous immunoglobulin (IVIG). Patients are more likely to be female, to have laboratory findings consistent with greater inflammation, and to have impaired systolic and diastolic function. They also exhibit resistance to IVIG more often and have higher rates of coronary artery dilation and aneurysm formation.10
Differential diagnoses for KD may include viral infections, scarlet fever, staphylococcal scalded skin syndrome, toxic shock syndrome, Rocky Mountain spotted fever, cervical lymphadenitis, drug hypersensitivity, Stevens-Johnson syndrome, systemic idiopathic arthritis, leptospirosis, and mercury hypersensitivity reaction.11
Work-Up
Laboratory evaluation of a patient with suspected KD should include:
- Complete blood count (CBC) with differential: leukocytosis, anemia, thrombocytosis that peaks in the third week is characteristic. A manual differential may reveal an increase in band forms.
- Acute phase reactants: If C-reactive protein (CRP) is 3 mg/dL or greater and erythrocyte sedimentation rate (ESR) is 40 mm/hr or greater, supplementary laboratory work-up should be done. Make sure not to cloud classic with incomplete KD; the stepwise lab evaluation only pertains to the latter.
- Liver panel: Elevated ALT and gamma-glutamyl transferase (GGT), mild hyperbilirubinemia, or hypoalbuminemia may be present.
- Urinalysis: Sterile pyuria may be present; if present, it may be of urethral origin, and catheterized samples could miss this finding.12