Case 2: A neonate in shock

During the fall, a 17-day-old boy was brought to the emergency department because of progressive feeding difficulty and lethargy after developing nasal congestion three days before presentation. The infant was born following an uncomplicated full term pregnancy and delivery. The family history was notable only for a five-year-old brother with a bicuspid aortic valve. Both his parents and brother had been recently ill with a cold. The infant was hypotonic and pale with signs of respiratory distress. His heart rate was 140 beats/min, respiratory rate was 64 breaths/min, systolic blood pressure was approximately 80 mmHg, oxygen saturation was 90% on room air and his rectal temperature was 36.5°C. Physical examination revealed hepatomegaly (4 cm to 5 cm below the costal margin) and diminished femoral and radial pulses; no rash was noted. Fluid resuscitation was begun immediately. However, after receiving 60 mL/kg of crystalloid solution, the patient became bradycardic (60 beats/min), requiring chest compressions, intubation and continuous infusion of vasopressors for stabilization. Initial laboratory findings included a mixed respiratory and metabolic acidosis, lymphocytosis, elevated transaminases and evidence of early disseminated intravascular coagulopathy. A chest x-ray demonstrated cardiomegaly (Figure 1). Blood, cerebrospinal fluid (CSF) and urine samples were sent for bacterial culture. Broad-spectrum antibiotics were begun, and the patient was admitted to the paediatric intensive care unit. Further investigations revealed the diagnosis. Chest radiographs at presentation. Anteroposterior (A) and lateral (B) views demonstrate cardiomegaly and mildly increased vascular markings. There is no evidence of parenchymal pulmonary disease. An echocardiogram showed a pericardial effusion, left ventricular dilatation and biventricular cardiac dysfunction with marked akinesia of the lateral and posterior walls of the left ventricle consistent with myocarditis. Enterovirus (EV) was subsequently detected by PCR from the patient’s blood, and gene sequencing identified the type as Coxsackie B4. Shock is defined as a mismatch between oxygen delivery and demand. When compensatory mechanisms such as tachycardia and peripheral vasoconstriction fail, end-organ perfusion is altered and diminished mental status, oliguria, weak central pulses and hypotension ensue. Shock may be classified as cardiogenic, hypovolemic or distributive (septic, anaphylactic). Cardiogenic shock is associated with signs of cardiac insufficiency (eg, hepatomegaly), new heart murmur, pulmonary congestion, or cardiomegaly and may be related to structural causes (ie, coarctation of the aorta), rhythm disturbances or, as in this case, inflammatory/infectious causes. Myocarditis is a rare but severe complication of EV infection. Inflammation of the myocardium has many potential causes. The most common is viral infection, with EV (especially Coxsackie B types 2–5) and adenovirus cited as the most frequent agents (1,2). Acute viral myocarditis is characterized by a biphasic presentation, often beginning with a nonspecific prodrome of upper respiratory or gastrointestinal tract symptoms. However, the acute infection may not always be recognized, especially in infants. There is significant variability in the ensuing manifestations of myocarditis, and the signs and symptoms can be vague (1,3). Although many cases go unnoticed and resolve spontaneously, congestive heart failure may develop within days to weeks, manifesting as respiratory distress, tachycardia, diaphoresis, poor feeding, irritability and lethargy. In young infants, tachypnea may be the presenting symptom. Patients with suspected viral myocarditis should be investigated with a chest radiograph, echocardiogram and electrocardiogram. Cardiomegaly is consistently present on chest radiographs of patients with congestive heart failure. The electrocardiogram may demonstrate nonspecific repolarization abnormalities (Figure 2). On echocardiography, ventricular function is reduced and a pericardial effusion may be present. Ancillary laboratory testing typically reveals elevated C-reactive protein levels and leukocytosis with lymphocyte predominance. Markers of myocardial injury (troponin and creatine kinase-MB) may also be elevated (1,3). The need for endomyocardial biopsy, previously considered the gold standard for diagnosis, is now questionable given its associated procedural risk, unreliable histopathological diagnostic criteria, and the advent of highly sensitive and noninvasive molecular detection techniques for the viral causes of myocarditis (3). Electrocardiograms at presentation (A) and 6 weeks later (B). Nearly-flat T waves are noted in the lateral leads during the acute phase of the illness (A). Six weeks later (B), persistent non-specific repolarization abnormalities are evidenced as inverted T waves laterally. Nonpoliovirus EVs cause an estimated 10 million symptomatic cases annually in the United States (4,5). In Canada, EV circulates principally from June to October. The most common presentation of EV is a nonspecific febrile illness. However, life-threatening EV disease, such as myocarditis or sepsis-like syndrome, is also seen. Young children that have yet to develop immunity to EVs are more susceptible to severe infections (4). Three laboratory methods are available to detect EV infection: serology, viral culture and nucleic acid amplification (eg, PCR). Serology is not considered clinically useful because of poor sensitivity and specificity and the impracticality of acute and convalescent blood testing. Viral culture and PCR may be performed on stool, respiratory, urine, blood or cerebrospinal fluid specimens. The sensitivity of EV culture varies from 0% to 80%, depending on the serotype, and generally takes three to eight days (5). In contrast, PCR assays are rapid and highly sensitive. Performing EV PCR on a combination of both blood and cerebrospinal fluid specimens may maximize diagnostic yield (6,7). There is no specific treatment available for EV myocarditis. Intravenous immunoglobulin has been used in life-threatening neonatal infections, but proof of efficacy is lacking (8). Coxsackievirus B acute myocarditis has a particularly poor prognosis for newborns, with mortality rates of up to 75% (7). Sequelae from EV myocarditis include the development of chronic arrhythmias and dilated cardiomyopathy, therefore necessitating the need for long-term follow-up (1). In our case, left ventricular function improved gradually despite the development of dilated cardiomyopathy. Viral myocarditis should be considered in the differential diagnosis of cardiogenic shock in neonates. EV infections are common, especially from June to October. Manifestations are usually non-specific (ie, fever) and self-limited but serious, life-threatening illness (eg, sepsis-like syndrome myocarditis) can occur. EV PCR testing of both blood and CSF can optimize diagnostic yield.

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