A 4-year-old boy is evaluated in the pediatric oncology clinic for an urgent follow-up. He… — USMLE Step 2 CK

A $4$ -year-old boy is evaluated in the pediatric oncology clinic for an urgent follow-up. He was diagnosed with standard-risk B-cell acute lymphoblastic leukemia (ALL) eight months ago and is currently in the maintenance phase of chemotherapy. Today, he has mild rhinorrhea but is otherwise active and playful. His mother reports that the patient spent the weekend with his $6$ -year-old cousin. Three days after the exposure, the cousin developed a low-grade fever and a diffuse vesicular rash that was subsequently diagnosed as chickenpox by a pediatrician. The patient has never had chickenpox and missed his routine preschool immunizations due to his cancer diagnosis. The patient's temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $95/60 \text{ mmHg}$ , heart rate is $100/\text{min}$ , and respiratory rate is $20/\text{min}$ . Physical examination reveals clear lungs, normal heart sounds, and no skin lesions. Laboratory studies show a leukocyte count of $3,200/\text{mm}^3$ with an absolute neutrophil count of $1,600/\text{mm}^3$ . The mother asks how to protect her son from the exposure. Which of the following is the most appropriate next step in management?

Administer varicella-zoster immune globulinAnswer
B
Administer the live-attenuated varicella vaccine
C
Admit the patient for empiric intravenous cefepime and vancomycin
D
Prescribe oral dexamethasone and albuterol nebulization
E
Contact the cousin's school directly to warn administrators of the outbreak

Answer

Administer varicella-zoster immune globulin to provide passive immunity, as the patient is immunocompromised and cannot safely receive the live vaccine.

The patient is susceptible to varicella and is severely immunocompromised due to ongoing maintenance chemotherapy for acute lymphoblastic leukemia (ALL). Varicella infection in this population can lead to severe complications, including pneumonia, encephalitis, and multiorgan failure. Because he is immunocompromised, the standard post-exposure prophylaxis with the live-attenuated varicella vaccine is strictly contraindicated. Instead, he requires passive immunization with varicella-zoster immune globulin (VZIG), ideally administered within 96 hours (up to 10 days) of exposure, to prevent or attenuate the disease.

Step-by-Step Solution

Assess the patient's immune status and susceptibility.

The patient is on active maintenance chemotherapy for ALL, making him significantly immunocompromised. He is susceptible because he has not had the disease or the vaccine.

Determines the safety profile of interventions (e.g., live vaccines are contraindicated in severe immunosuppression).

Evaluate the clinical event.

The patient had a significant exposure to varicella-zoster virus (spending the weekend with a contagious cousin).

Significant exposure in a susceptible, high-risk host requires immediate post-exposure prophylaxis.

Select the appropriate prophylactic agent.

Varicella-zoster immune globulin (VZIG) is selected over the active varicella vaccine.

Since active immunization with a live-attenuated virus could cause severe disease in this immunocompromised child, passive immunization with pre-formed antibodies (VZIG) is the standard of care.

Key Concept

Management of viral exposures and vaccine contraindications in pediatric oncology patients.

Estimated Time:1m 15s

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