Incomplete Kawasaki disease with coronary artery aneurysms in an infant presenting with persistent fever despite pneumonia treatment

Patel Aanal; Al-Sabri Mohammed; Nguyen Daren; Levine Michael

doi:10.22470/pemj.2026.01578

Abstract

Incomplete Kawasaki disease (KD) in infants often presents without classic clinical features, increasing the risk of delayed diagnosis and coronary complications. We report a previously healthy 9-month-old male who presented to an emergency department with a 15-day history of fever and dry cough, despite amoxicillin therapy for presumed pneumonia. On arrival, the infant was febrile and tachycardic, with stable hemodynamics and a benign finding of physical examination. Laboratory evaluation showed high values of inflammatory markers. The persistent fever and high values of inflammatory markers despite the antimicrobial therapy prompted consideration of incomplete KD as an alternative diagnosis. This diagnosis was confirmed by multiple coronary artery aneurysms shown on an echocardiogram. His fever was resolved by the use of intravenous immunoglobulin, methylprednisolone, and high-dose aspirin. This case highlights the importance of maintaining a high index of suspicion for incomplete KD in infants with persistent fever and evolving inflammatory findings, despite appropriate antimicrobial therapy.

Key Words: Coronary Aneurysm; Fever; Mucocutaneous Lymph Node Syndrome; Pediatrics; Vasculitis

Introduction

Fever is a ubiquitous feature of pediatric illness, and Kawasaki disease (KD) is frequently overlooked when an alternative infectious diagnosis, such as pneumonia, is present. Infants often lack the classic mucocutaneous features emphasized in medical training, leading clinicians to attribute persistent fever to treatment failure or prolonged recovery from the infection. Early laboratory clues include markedly high value of C-reactive protein (CRP) or erythrocyte sedimentation rate, leukocytosis, thrombocytosis, anemia, and hypoalbuminemia. This case exemplifies how incomplete KD can masquerade as pneumonia, and highlights the importance of systemic reassessment using established diagnostic algorithms. The legal guardians of the patient provided informed consent to share the details of this case.

Case

A fully immunized 9-month-old male born at term with no complications presented to our emergency department with a 15-day history of daily fever (maximum 39.8 °C) and persistent dry cough as detailed in Table. He had mild fatigue and intermittent loose stools since starting antibiotic therapy. Oral intake and urine output remained at baseline. There were no conjunctivitis, oral mucosal changes, extremity swelling, vomiting, diarrhea, or sick contacts. A faint, transient abdominal rash was reported several days earlier. Past medical history was notable for a respiratory syncytial virus infection 1 month earlier.

From illness days 1–15, the infant received intermittent acetaminophen and ibuprofen for fever control. He was prescribed a 7-day course of amoxicillin starting on day 9 of illness for presumed pneumonia. No systemic corticosteroids or other immunomodulatory agents were administered at that time. Despite the interventions, he continued to have persistent daily fevers.

Vital signs on arrival at the emergency department were as follows: blood pressure, 92/54 mmHg; heart rate, 149 beats/minute; respiratory rate, 26 breaths/minute; temperature, 38.6 °C (later peak at 40.2 °C); and oxygen saturation, 99% on room air. Weight was 9.1 kg and length was 71.9 cm. Fever transiently improved with antipyretics but recurred within hours. On physical examination, he was well appearing, interactive, and nontoxic. No conjunctival injection, oral mucosal changes, cervical lymphadenopathy, extremity edema, or rashes was observed. Cardiopulmonary examination was clear without any focal findings or murmurs. The abdomen was soft and nontender.

Chest radiography showed right upper lobe interstitial markings without focal consolidation, which was interpreted as consistent with resolving pneumonia or another inflammatory process by the attending physician (Figure).

Laboratory findings were as follows: leukocytes, 16.3 × 10³/μL (neutrophils, 11.2 × 10³/μL); hemoglobin, 9.8 g/dL; platelets, 804 × 10³/μL; CRP, 234 mg/L; erythrocyte sedimentation rate, 78 mm/hour; natrium, 132 mmol/L; albumin, 2.6 g/dL; alanine aminotransferase, 68 U/L; and ferritin, 250 ng/mL (reference value, 22–275 ng/mL). Immunoglobulin testing showed concentrations of immunoglobulin G at 519 mg/dL (540–1,822 mg/dL) and of immunoglobulin M at 115 mg/dL (22–293 mg/dL). Serologic testing was negative for Epstein-Barr virus and parvovirus B19, while blood cultures showed no growth after incubation.

Despite broad-spectrum antibiotics, ceftriaxone and azithromycin, the infant continued to have high-grade fever. Based on the persistent fever, high inflammatory markers, thrombocytosis, and anemia, he was hospitalized for possible treatment failure of pneumonia, sepsis, or incomplete KD, and was consulted a pediatric cardiologist for relevant evaluation.

Cardiac evaluation included an electrocardiography showing a normal sinus rhythm with a corrected QT interval of 380 msec. Transthoracic echocardiography performed on hospital day 1 (illness day 15) showed dilated coronary arteries, with Z-scores as follows: the left main coronary artery, + 2.8; right coronary artery, + 3.5; and left anterior descending artery, + 9.0, consistent with KD [1]. The Z-scores were calculated by the pediatric cardiologist using standard reference equations. No absolute coronary artery measurements were available in the report.

The infant met criteria for incomplete KD: fever >5 days; CRP, >30 mg/L; platelets, >450 × 10³/L after day 7; leukocytes, >15 × 10³/L; albumin, <3.0 g/dL; high alanine aminotransferase; and the coronary artery abnormalities on the echocardiography [1]. Treatment was initiated with intravenous immunoglobulin (IVIG; 2 g/kg as a single dose), high-dose aspirin (50 mg/kg/day divided every 6 hours), and intravenous methylprednisolone (2 mg/kg/day divided every 12 hours) [1]. Fever resolved within 24 hours of the IVIG administration. On hospital day 5, he was discharged uneventfully with a cardiology follow-up arranged (Table).

A 1-month follow up echocardiography demonstrated an interval improvement, with the left main coronary artery at 3.0 mm (Z-score, + 2.6), right coronary artery measuring at 2.4 mm (+ 2.6), and left anterior descending artery at 3.2 mm (+ 6.0). A small pericardial effusion and trace mitral regurgitation were also noted with preserved ventricular systolic function.

Discussion

This case highlights critical challenges in diagnosis of incomplete KD in pediatric emergency settings. First, anchoring bias and diagnostic momentum contributed to delayed recognition of incomplete KD. The prior diagnosis of pneumonia led the clinicians to attribute persistent fever to poor antibiotic response rather than to consider an inflammatory non-infectious etiology, such as KD. Similar patterns of anchoring have been widely reported in literature on KD and are associated with delayed administration of IVIG [2].

Second, incomplete KD predominated in infants. Infants presenting without classic mucocutaneous criteria for KD are frequently misdiagnosed with pneumonia, viral illness, or urinary tract infection [3]. The earliest diagnostic clues are often provided by laboratory abnormalities, such as thrombocytosis and CRP values exceeding typical infectious ranges [4].

Third, the CRP concentration of 234 mg/L and platelet count of 804 × 10³/μL exceeded values typically observed in such pneumonia [4]. Persistent fever despite appropriate antibiotic therapy should prompt consideration of the differential diagnosis, including KD, multisystem inflammatory syndrome in children, or autoinflammatory conditions.

Fourth, infants are at high risk for early coronary artery involvement, and delayed diagnosis is strongly associated with increased aneurysm formation, particularly in younger patients [5]. He already exhibited medium-sized coronary aneurysms at the time of initial echocardiography, emphasizing how rapidly the complication could occur.

Finally, it was pivotal to involve the cardiologist at the early phase. Prompt echocardiography led to timely diagnosis and administration of IVIG and steroids, which have shown to reduce coronary progression. Increasing evidence suggests that KD frequently includes pulmonary manifestations, and recognition of the overlap of manifestations between of KD and of pneumonia may reduce misdiagnosis in future cases.

Notes

Author contributions

Conceptualization: all authors

Data curation, Formal analysis, Investigation, Project administration, Validation, and Visualization: PA

Funding acquisition: not applicable

Methodology: PA and ASM

Resources: LM

Supervision: ASM and LM

Writing-original draft: PA

Writing-review and editing: all authors

All authors read and approved the final manuscript

Conflicts of interest

No potential conflicts of interest relevant to this article were reported.

Funding sources

No funding source relevant to this article was reported.

Figure.

Plain chest radiograph on illness days 9 (A) versus 15 (B) showing right upper lobe interstitial markings without focal consolidation (asterisk, A).

Table.

Timeline of illness

Day of illness	Key events
Day 1	At an outside hospital, the infant was detected with norovirus and adenovirus and treated symptomatically against intermittent fevers.
Day 9	At our ED, he obtained a diagnosis of pneumonia and started a 7-day course of amoxicillin. No laboratory studies obtained.
Days 9–15	Persistent daily fevers (101 °F–102 °F [38.3 ℃–38.8 ℃]) and cough despite the antibiotic therapy.
Day 15 (HD 1)	He returned to the ED for the persistent fever (up to 104.4 °F [40.2 ℃]).
	Laboratory findings: C-reactive protein, 234 mg/L; and platelets, 804 × 10³/μL.
	Hospitalized for possible treatment failure of pneumonia, sepsis, or incomplete Kawasaki disease.
	Started on intravenous ceftriaxone and oral azithromycin.
	Cardiology consulted.
	Echocardiography showed coronary artery aneurysms (e.g., left anterior descending artery, Z-score = + 9.0).
	He started on treatment of IVIG, high-dose aspirin, and corticosteroids.
HD 2	Fever resolved within the first 24 hours.
HD 5	Transitioned to low-dose aspirin and clopidogrel and discharged uneventfully.

ED: emergency department, HD: hospital day, IVIG: intravenous immunoglobulin.

References

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2. Petrarca L, Nenna R, Versacci P, Frassanito A, Cangiano G, Nicolai A, et al. Difficult diagnosis of atypical Kawasaki disease in an infant younger than six months: a case report. Ital J Pediatr 2017;43:30.

3. Idris I, Awadelkarim AM, Saad E, Dayco J, Beker S. Incomplete Kawasaki disease in an infant: a case report and literature review. Cureus 2022;14:e22122.

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